**3.4 Igneous seismic geomorphology**

Seismic geomorphology is the application of analytical techniques to study ancient buried sedimentary systems imaged by 3D seismic data [18, 20, 75]. Similarly, igneous seismic geomorphology analyses the 3D characteristics of buried volcanoes and shallow crustal intrusions from a geomorphological perspective [29]. This technique is based on the extraction of horizons and slices from the seismic volume at scales and geometries comparable to modern volcanic morphologies (**Figures 1** and **6**). A variety of analytical techniques, such as opacity rendering, spectral decomposition, iso-proportional slicing, and mapping of geobodies can be applied to image the geometric aspects, spatio-temporal distribution and relationship of seismic units [76].

When integrated with seismic and sequence stratigraphy, seismic geomorphology provides background information to interpret the morphology and architecture of buried volcanoes (**Figure 7**). In outcrop, the morphological characteristics of volcanoes provide insights into past eruptive styles, edifice growth mechanisms, and

### **Figure 7.**

*Examples of techniques used to recognise igneous rocks buried in sedimentary basis. (a) Amplitude seismic section displaying typical saucer-shape sill and related vents located above the termination of the sill, Bight Basin, southern Australia. From Reynolds et al. [15]. (b) 2D seismic cross-section showing a monzogabbro intrusion and associated volcanogenic deposits, tied to lithologies penetrated by the Resolution-1 exploration drillhole, Canterbury Basin, New Zealand. From Bischoff et al. [22, 37, 53]. (c) 2D amplitude seismic crosssection illustrating the main architectural elements of a small mound-shaped volcano buried in the Canterbury Basin, New Zealand. From Bischoff et al. [22, 37, 53]. (d) Photograph illustrating the main architectural elements of a Holocene cinder cone in the La Payunia volcanic field, Argentina. Note the similar morphology of volcanoes in seismic imagery and modern outcropping analogues.*

**81**

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins*

cone degradation experienced during their complete history [21, 77]. Correlating the morphological aspects of buried and outcropping volcanoes can assist in developing the best possible model for the volcanic emplacement in its surrounding environments, including prediction of lithologies, stratigraphic architecture, and

The concept of architectural elements was introduced to sedimentary geology during the 1980s' and 1990s' to document the fundamental building blocks of fluvial and deep-water systems [20, 78, 79]. The systematic documentation of the variety and arrangement of architectural elements such as channels, levees, and accretionary bars are critical for the interpretation of buried sedimentary environments, with particular relevance to the 3D interpretation of seismic reflection

An architectural element is defined as a three-dimensional genetically related rock unit characterised by its geometry, facies, composition, scale, and boundingsurfaces, and is the product of a particular process or suite of processes occurring within a depositional system [81]. The architectural elements approach investigates the internal arrangement and external bounding-surfaces that delimit co-genetic lithofacies and seismic units [47]. These elements are typically described at a

Volcanic landforms including their small-scale variants such as basaltic monogenetic cinder cones and maar-diatreme volcanoes also comprise a combination of particular building blocks with scales comparable to those of sedimentary macroforms. For example, cinder cones typically display a central crater with marginal tephra flanks, while a maar volcano characteristically has a diatreme circled by a tephra ring [6, 83]. Each of these fundamental volcanic building blocks (i.e. architectural elements) are often >100 m in horizontal and vertical dimensions [72], therefore, they may be recognisable in seismic reflection datasets (**Figures 6** and **7**). Facies models of modern and ancient outcropping volcanoes show a systematic variation of macroforms and lithofacies, which are typically spatially distributed according to their distance from eruptive centres [21, 67, 84]. Comparing the variety and arrangement of buried architectural elements with volcanic facies models available in the literature helps us to predict the three-dimensional patterns of igneous and sedimentary lithofacies within buried volcanic systems (**Figures 4, 6** and **7**). This information can then be used to assist the interpretation of the geological processes that formed the volcanoes now buried in the subsurface [52, 53].

–104

meters), using [82]

geological processes occurred during their evolution (**Figures 6** and **7**).

*DOI: http://dx.doi.org/10.5772/intechopen.95282*

**3.5 Architectural elements of buried volcanoes**

scale of macroforms (i.e. bedforms with lengths of 102

**4. Morphology and architecture of buried volcanic systems**

geometries of intrusive bodies and the location of eruptive centres [86–88].

The majority of melt generated by igneous activity likely fails to reach the Earth's surface [85]. Within sedimentary basins, magma often forms widespread plumbing networks that can extend laterally for tens of kilometres before it erupts [43]. The movement of magma through the shallow layers of the crust and its interaction with heterogeneous host rocks and faults are primary parameters that constrain the

Volcanic plumbing systems emplaced in sedimentary strata comprise numerous intrusive bodies of various shapes and sizes. These bodies are broadly classified into

**4.1 Shallow subvolcanic intrusions**

datasets [80].

terminology.

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins DOI: http://dx.doi.org/10.5772/intechopen.95282*

cone degradation experienced during their complete history [21, 77]. Correlating the morphological aspects of buried and outcropping volcanoes can assist in developing the best possible model for the volcanic emplacement in its surrounding environments, including prediction of lithologies, stratigraphic architecture, and geological processes occurred during their evolution (**Figures 6** and **7**).

### **3.5 Architectural elements of buried volcanoes**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

**3.4 Igneous seismic geomorphology**

ship of seismic units [76].

enclosing sedimentary strata (**Figure 7**) [30]. More recently, the use of machine learning techniques and artificial neural networks have been applied to delineate igneous seismic facies [74]. Description of igneous seismic units can be used to interpret volcanic landforms and different parts of volcanic systems. For example, cone-type volcanoes such as cinder cones and stratovolcanoes typically display a pair of inward- and outward-dipping reflections that mark the location of a central crater and peripheral flanks. Optimal characterisation of buried volcanoes can be obtained by analysing the igneous seismic facies as part of a genetically related network in different scales of observation, which consist in mapping intrusive and extrusive igneous seismic units into a unified interpretation framework [29, 52, 73].

Seismic geomorphology is the application of analytical techniques to study ancient buried sedimentary systems imaged by 3D seismic data [18, 20, 75].

Similarly, igneous seismic geomorphology analyses the 3D characteristics of buried volcanoes and shallow crustal intrusions from a geomorphological perspective [29]. This technique is based on the extraction of horizons and slices from the seismic volume at scales and geometries comparable to modern volcanic morphologies (**Figures 1** and **6**). A variety of analytical techniques, such as opacity rendering, spectral decomposition, iso-proportional slicing, and mapping of geobodies can be applied to image the geometric aspects, spatio-temporal distribution and relation-

When integrated with seismic and sequence stratigraphy, seismic geomorphology provides background information to interpret the morphology and architecture of buried volcanoes (**Figure 7**). In outcrop, the morphological characteristics of volcanoes provide insights into past eruptive styles, edifice growth mechanisms, and

*Examples of techniques used to recognise igneous rocks buried in sedimentary basis. (a) Amplitude seismic section displaying typical saucer-shape sill and related vents located above the termination of the sill, Bight Basin, southern Australia. From Reynolds et al. [15]. (b) 2D seismic cross-section showing a monzogabbro intrusion and associated volcanogenic deposits, tied to lithologies penetrated by the Resolution-1 exploration drillhole, Canterbury Basin, New Zealand. From Bischoff et al. [22, 37, 53]. (c) 2D amplitude seismic crosssection illustrating the main architectural elements of a small mound-shaped volcano buried in the Canterbury Basin, New Zealand. From Bischoff et al. [22, 37, 53]. (d) Photograph illustrating the main architectural elements of a Holocene cinder cone in the La Payunia volcanic field, Argentina. Note the similar morphology of* 

*volcanoes in seismic imagery and modern outcropping analogues.*

**80**

**Figure 7.**

The concept of architectural elements was introduced to sedimentary geology during the 1980s' and 1990s' to document the fundamental building blocks of fluvial and deep-water systems [20, 78, 79]. The systematic documentation of the variety and arrangement of architectural elements such as channels, levees, and accretionary bars are critical for the interpretation of buried sedimentary environments, with particular relevance to the 3D interpretation of seismic reflection datasets [80].

An architectural element is defined as a three-dimensional genetically related rock unit characterised by its geometry, facies, composition, scale, and boundingsurfaces, and is the product of a particular process or suite of processes occurring within a depositional system [81]. The architectural elements approach investigates the internal arrangement and external bounding-surfaces that delimit co-genetic lithofacies and seismic units [47]. These elements are typically described at a scale of macroforms (i.e. bedforms with lengths of 102 –104 meters), using [82] terminology.

Volcanic landforms including their small-scale variants such as basaltic monogenetic cinder cones and maar-diatreme volcanoes also comprise a combination of particular building blocks with scales comparable to those of sedimentary macroforms. For example, cinder cones typically display a central crater with marginal tephra flanks, while a maar volcano characteristically has a diatreme circled by a tephra ring [6, 83]. Each of these fundamental volcanic building blocks (i.e. architectural elements) are often >100 m in horizontal and vertical dimensions [72], therefore, they may be recognisable in seismic reflection datasets (**Figures 6** and **7**).

Facies models of modern and ancient outcropping volcanoes show a systematic variation of macroforms and lithofacies, which are typically spatially distributed according to their distance from eruptive centres [21, 67, 84]. Comparing the variety and arrangement of buried architectural elements with volcanic facies models available in the literature helps us to predict the three-dimensional patterns of igneous and sedimentary lithofacies within buried volcanic systems (**Figures 4, 6** and **7**). This information can then be used to assist the interpretation of the geological processes that formed the volcanoes now buried in the subsurface [52, 53].

## **4. Morphology and architecture of buried volcanic systems**

### **4.1 Shallow subvolcanic intrusions**

The majority of melt generated by igneous activity likely fails to reach the Earth's surface [85]. Within sedimentary basins, magma often forms widespread plumbing networks that can extend laterally for tens of kilometres before it erupts [43]. The movement of magma through the shallow layers of the crust and its interaction with heterogeneous host rocks and faults are primary parameters that constrain the geometries of intrusive bodies and the location of eruptive centres [86–88].

Volcanic plumbing systems emplaced in sedimentary strata comprise numerous intrusive bodies of various shapes and sizes. These bodies are broadly classified into sheet-like intrusions such as dykes, sills and cone sheets, and more massive equidimensional forms, including laccoliths, plugs, and plutons [24, 89, 90]. Sheet-like intrusions prevail in sedimentary basins because magma tends to propagate through and along with weakness plans of the host strata and faults. Dykes are understood to be the main vertical pathways for magma feeding eruptive centres [91], while sills mostly distribute melts laterally across the basin [92]. This is because, by definition, sills are dominantly parallel with the usual sub-horizontal basin strata (including layers of lava or sedimentary rocks), whilst dykes dominantly cross-cut layering in basin host rocks.

However, magmatic intrusions may extend for tens to hundreds of kilometres [93–95], limiting our ability to observe their complete geometry exclusively from outcrops. Seismic reflection profiles can provide large scale images (tens to hundreds of km's) of entire intrusive bodies, allowing us to describe their geometric aspects, lateral and vertical dimension, and interconnectivity in detail (**Figure 8**). Interpretation of seismic data from volcanic basins has revealed that sills can locally display geometries that are discordant with the host rocks. These discordant sills are described in terms of their geometry in relation to the orientation of the host strata, comprising morphologies such as transgressive, step-wise, and saucer- and v-shaped sills [59, 96]. This improved understanding of the migration of magma through interconnected intrusions demonstrated the critical role of sills in transferring

### **Figure 8.**

*Seismic examples and outcrop analogues of tabular sills and dykes. (a) Amplitude seismic display across small vents and shallow correlative intrusions of the Maahunui volcanic field, offshore New Zealand [22]. (b) A series of extensive flat-lying sills emplaced parallel to marine strata of the Neuquén Basin, Argentina. (c and d) Sub-vertical dykes cross-cutting a sequence of lava and pyroclastic flows of the Banks Peninsula compound volcano, New Zealand.*

**83**

**Figure 9.**

*inclined sheets cross-cutting the host strata.*

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins*

Numerous sills in sedimentary basins have a saucer-shaped geometry consisting

magma from depths to upper layers of the crust, which has been reinforced by

of a flat-lying inner sill connected to outer inclined sheets (**Figure 9**). Saucershaped sills are usually (but not always) identified in 2D seismic lines by a concaveupward high-amplitude reflection located below an anticlinal fold, suggesting that emplacement of the sill uplifted the overlying strata [98]. Reflections displaying onlap terminations on the top of these folds typically indicate the timing of intrusion emplacement [99]. The upper termination of the inclined sheets is often associated with small craters and cones that erupted at the paleosurface, suggesting a relationship between saucer-sills and vent complexes (**Figure 6a**). The vent complexes can be of both hydrothermal (phreatic) and magmatic origin [58–60]. Dykes and other thin (<50 m) sub-vertical intrusions (i.e. conduits) can be inferred using principles from fault interpretation, by the presence of narrow and sub-vertical bright discontinuities associated with disrupted enclosing reflections [52, 100]. The application of this disrupted-reflector criteria for dyke identification is more likely to be accurate if the sub-vertical discontinuities are located below a vent zone or related to flat-lying intrusions. Dike swarms have been interpreted by steeply inclined high-to-moderate amplitude reflections cross-cutting sedimentary

*DOI: http://dx.doi.org/10.5772/intechopen.95282*

observations from laboratory experiments [89, 97].

strata in offshore Norway [101] and New Zealand (**Figure 8a**).

*Seismic and outcrop examples showing the typical geometry of saucer-shaped intrusions. (a) Envelope display across a saucer-intrusion of Eocene age emplaced in Cretaceous to Paleocene strata of the Deepwater Taranaki Basin, New Zealand. (b) Saucer-intrusion emplaced in sedimentary strata of the Karoo Basin, South Africa. Cross-section (c) and in plain view (d) amplitude display of the intrusion shown in (a). (e) Composite 3D perspective display of an amplitude cross-section and a time-slice of a spectrally decomposed seismic cube across the intrusion in (a). (f) Same view as (e) extracting the seismic geobody that corresponds to the 3D geometry of the intrusion. This hybrid intrusion comprises an inner sill parallel to the sedimentary strata, and peripheral* 

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins DOI: http://dx.doi.org/10.5772/intechopen.95282*

magma from depths to upper layers of the crust, which has been reinforced by observations from laboratory experiments [89, 97].

Numerous sills in sedimentary basins have a saucer-shaped geometry consisting of a flat-lying inner sill connected to outer inclined sheets (**Figure 9**). Saucershaped sills are usually (but not always) identified in 2D seismic lines by a concaveupward high-amplitude reflection located below an anticlinal fold, suggesting that emplacement of the sill uplifted the overlying strata [98]. Reflections displaying onlap terminations on the top of these folds typically indicate the timing of intrusion emplacement [99]. The upper termination of the inclined sheets is often associated with small craters and cones that erupted at the paleosurface, suggesting a relationship between saucer-sills and vent complexes (**Figure 6a**). The vent complexes can be of both hydrothermal (phreatic) and magmatic origin [58–60].

Dykes and other thin (<50 m) sub-vertical intrusions (i.e. conduits) can be inferred using principles from fault interpretation, by the presence of narrow and sub-vertical bright discontinuities associated with disrupted enclosing reflections [52, 100]. The application of this disrupted-reflector criteria for dyke identification is more likely to be accurate if the sub-vertical discontinuities are located below a vent zone or related to flat-lying intrusions. Dike swarms have been interpreted by steeply inclined high-to-moderate amplitude reflections cross-cutting sedimentary strata in offshore Norway [101] and New Zealand (**Figure 8a**).

### **Figure 9.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

sheet-like intrusions such as dykes, sills and cone sheets, and more massive equidimensional forms, including laccoliths, plugs, and plutons [24, 89, 90]. Sheet-like intrusions prevail in sedimentary basins because magma tends to propagate through and along with weakness plans of the host strata and faults. Dykes are understood to be the main vertical pathways for magma feeding eruptive centres [91], while sills mostly distribute melts laterally across the basin [92]. This is because, by definition, sills are dominantly parallel with the usual sub-horizontal basin strata (including layers of lava or sedimen-

However, magmatic intrusions may extend for tens to hundreds of kilometres [93–95], limiting our ability to observe their complete geometry exclusively from outcrops. Seismic reflection profiles can provide large scale images (tens to hundreds of km's) of entire intrusive bodies, allowing us to describe their geometric aspects, lateral and vertical dimension, and interconnectivity in detail (**Figure 8**). Interpretation of seismic data from volcanic basins has revealed that sills can locally display geometries that are discordant with the host rocks. These discordant sills are described in terms of their geometry in relation to the orientation of the host strata, comprising morphologies such as transgressive, step-wise, and saucer- and v-shaped sills [59, 96]. This improved understanding of the migration of magma through interconnected intrusions demonstrated the critical role of sills in transferring

tary rocks), whilst dykes dominantly cross-cut layering in basin host rocks.

**82**

**Figure 8.**

*volcano, New Zealand.*

*Seismic examples and outcrop analogues of tabular sills and dykes. (a) Amplitude seismic display across small vents and shallow correlative intrusions of the Maahunui volcanic field, offshore New Zealand [22]. (b) A series of extensive flat-lying sills emplaced parallel to marine strata of the Neuquén Basin, Argentina. (c and d) Sub-vertical dykes cross-cutting a sequence of lava and pyroclastic flows of the Banks Peninsula compound* 

*Seismic and outcrop examples showing the typical geometry of saucer-shaped intrusions. (a) Envelope display across a saucer-intrusion of Eocene age emplaced in Cretaceous to Paleocene strata of the Deepwater Taranaki Basin, New Zealand. (b) Saucer-intrusion emplaced in sedimentary strata of the Karoo Basin, South Africa. Cross-section (c) and in plain view (d) amplitude display of the intrusion shown in (a). (e) Composite 3D perspective display of an amplitude cross-section and a time-slice of a spectrally decomposed seismic cube across the intrusion in (a). (f) Same view as (e) extracting the seismic geobody that corresponds to the 3D geometry of the intrusion. This hybrid intrusion comprises an inner sill parallel to the sedimentary strata, and peripheral inclined sheets cross-cutting the host strata.*

## **4.2 Clusters of small-volume craters and cones**

Clusters of discrete, small-volume (i.e. <1 km3 ) craters and cones occur in most tectonic settings around the world. These clusters often contain tens to hundreds of volcanoes associated with rifting (e.g. Assab Volcanic Field, Ethiopia), intraplate volcanism (Newer Volcanic Province, Australia) and subduction zones (Pinacate Volcanic Field, Mexico). Typically, they comprise basaltic monogenetic volcanoes such as scoria cones, tuff rings, maars-diatremes, and hydrothermal vents, although some examples can also be of dacitic, phonolithic, trachytic, and rhyolitic composition [72, 102]. The basaltic fields are commonly derived from mantle melts with minor fractional crystallisation and little crustal assimilation, sourcing low-viscosity magmas that can feed widespread lava-flow fields adjacent to the craters and cones [103]. Clusters of dacitic to rhyolitic lava domes and explosive vents are rare and more commonly erupted as the final events of large silicic caldera-forming cycles, or from their associated fissures systems [104, 105].

The primary morphology of small craters and cones can display simple or complex geometries, which are determined by parameters such as the content of volatiles dissolved in the magma and water-melt interactions in the environment surrounding the eruption [83, 106]. Small mafic volcanoes dominated by a mound- or conical-shaped geometry (i.e. spatter, scoria, and tuff cones) are often constructed by accumulation of fragmental volcanic material (tephra) ejected by relatively low-energy pyroclastic eruptions such as fire-fountaining, Strombolian and Vulcanian eruptive styles (**Figure 10a**-**d**). Although each mound-shaped volcano presents characteristic morphometric forms, their simpler end-members all share a systematic distribution of macroforms in relation to the vent zone. This typical macroform distribution comprises of a proximal central crater circled by peripheral flanks that are enclosed by a distal tephra (or lava field) apron [6]. Average sizes of cone-shaped volcanoes are ca 300 m height and 1 km basal width, with spatter cones having the smallest dimensions and tuff cones the largest sizes [72]. By contrast, small volcanoes dominated by a crater-shaped geometry (i.e. tuff rings and maar-diatremes) typically result from phreatomagmatic eruptions (including Surtseyan styles) triggered by molten-fuel-coolant interactions of magma, water, CO2, and thermogenic gases [107, 108]. These volcanoes have craters up to 3 km in width and maximum depth up to 500 m. The distribution of macroforms in a tuff ring consists of a central crater circled by a peripheral ejecta ring and a debris apron [109], while Maar-diatremes display a root zone, a lower unbedded and upper bedded diatreme, an ejecta ring, and an associated debris apron (**Figure 10e**-**h**).

The seismic expression of small craters and cones are comparable to geometries observed in outcropping volcanoes [9, 27]. In seismic cross-sections, mound-shaped volcanoes are inferred from mounds that built-up above a relatively flat pre-eruptive surface. Chaotic or inward-dipping reflections at the centre of the mounds suggest the location of the vent zone, while lateral inclined, parallel, continuous or disrupted outward-dipping reflections indicate the position of the flanks (**Figure 10a**-**d**). The mounds may or may not contain peripheral sub-horizontal continuous to discontinuous high-amplitude reflections that represent lava-flow fields and tephra aprons. In contrast, the crater-shaped volcanoes show V-shaped excavations into the preeruptive surface. These craters typically contain unbedded, disrupted and chaotic reflections at the base (i.e. lower diatreme), and discontinuous to bedded reflections at the top (upper diatreme). The crater-shaped volcanoes are often circled by moderate to high-amplitude reflections that likely represent material ejected by large pyroclastic eruptions [2, 53].

**85**

**Figure 10.**

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins*

The deduction of mounds- and crater-shaped seismic anomalies being igneous in origin can be reinforced by the presence of artefacts such as pull-up of seismic velocities (**Figure 6a**), indicating that rocks within the anomalies have a much higher acoustic velocity than the surrounding strata [25, 35]. In addition, doming of reflectors overlying mound-shaped volcanoes (**Figure 8a**) is common where

*Basin, Australia [9]. (h) Oblique, TWT view of the proposed maar-diatreme in (g).*

*Illustrations of the architecture of small-volume cones and craters. (a) Schematic cross-section through a cinder cone adapted from Kereszturi and Németh [6]. (b) Seismic cross-section highlighting the general morphology and seismic response of a cinder cone and associated lava field buried offshore Taranaki Basin, New Zealand. Note the characteristic inward-dipping reflections towards the crater and the outward-dipping structure away from the vent zone. (c) Plan view spectral decomposition of the cinder cone taken from the Winnie 3D survey, Eromanga Basin, Australia, highlighting the cone-shaped morphology of the vent and associated extensive lava field [9]. (d) Horizon mapping of the top surface of the cinder cone shown in (c). (d) Cross-section through a maar-diatreme adapted from Kereszturi and Németh [6]. (f) A seismic line across a maar-diatreme volcano buried in the offshore Banks Peninsula, New Zealand [22]. The chaotic reflections indicate deep excavations of the pre-eruptive subsurface. (g) Plan view spectral decomposition of a maar-diatreme buried in the Eromanga* 

*DOI: http://dx.doi.org/10.5772/intechopen.95282*

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins DOI: http://dx.doi.org/10.5772/intechopen.95282*

### **Figure 10.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

**4.2 Clusters of small-volume craters and cones**

systems [104, 105].

apron (**Figure 10e**-**h**).

pyroclastic eruptions [2, 53].

Clusters of discrete, small-volume (i.e. <1 km3

in most tectonic settings around the world. These clusters often contain tens to hundreds of volcanoes associated with rifting (e.g. Assab Volcanic Field, Ethiopia), intraplate volcanism (Newer Volcanic Province, Australia) and subduction zones (Pinacate Volcanic Field, Mexico). Typically, they comprise basaltic monogenetic volcanoes such as scoria cones, tuff rings, maars-diatremes, and hydrothermal vents, although some examples can also be of dacitic, phonolithic, trachytic, and rhyolitic composition [72, 102]. The basaltic fields are commonly derived from mantle melts with minor fractional crystallisation and little crustal assimilation, sourcing low-viscosity magmas that can feed widespread lava-flow fields adjacent to the craters and cones [103]. Clusters of dacitic to rhyolitic lava domes and explosive vents are rare and more commonly erupted as the final events of large silicic caldera-forming cycles, or from their associated fissures

The primary morphology of small craters and cones can display simple or complex geometries, which are determined by parameters such as the content of volatiles dissolved in the magma and water-melt interactions in the environment surrounding the eruption [83, 106]. Small mafic volcanoes dominated by a mound- or conical-shaped geometry (i.e. spatter, scoria, and tuff cones) are often constructed by accumulation of fragmental volcanic material (tephra) ejected by relatively low-energy pyroclastic eruptions such as fire-fountaining, Strombolian and Vulcanian eruptive styles (**Figure 10a**-**d**). Although each mound-shaped volcano presents characteristic morphometric forms, their simpler end-members all share a systematic distribution of macroforms in relation to the vent zone. This typical macroform distribution comprises of a proximal central crater circled by peripheral flanks that are enclosed by a distal tephra (or lava field) apron [6]. Average sizes of cone-shaped volcanoes are ca 300 m height and 1 km basal width, with spatter cones having the smallest dimensions and tuff cones the largest sizes [72]. By contrast, small volcanoes dominated by a crater-shaped geometry (i.e. tuff rings and maar-diatremes) typically result from phreatomagmatic eruptions (including Surtseyan styles) triggered by molten-fuel-coolant interactions of magma, water, CO2, and thermogenic gases [107, 108]. These volcanoes have craters up to 3 km in width and maximum depth up to 500 m. The distribution of macroforms in a tuff ring consists of a central crater circled by a peripheral ejecta ring and a debris apron [109], while Maar-diatremes display a root zone, a lower unbedded and upper bedded diatreme, an ejecta ring, and an associated debris

The seismic expression of small craters and cones are comparable to geometries observed in outcropping volcanoes [9, 27]. In seismic cross-sections, mound-shaped volcanoes are inferred from mounds that built-up above a relatively flat pre-eruptive surface. Chaotic or inward-dipping reflections at the centre of the mounds suggest the location of the vent zone, while lateral inclined, parallel, continuous or disrupted outward-dipping reflections indicate the position of the flanks (**Figure 10a**-**d**). The mounds may or may not contain peripheral sub-horizontal continuous to discontinuous high-amplitude reflections that represent lava-flow fields and tephra aprons. In contrast, the crater-shaped volcanoes show V-shaped excavations into the preeruptive surface. These craters typically contain unbedded, disrupted and chaotic reflections at the base (i.e. lower diatreme), and discontinuous to bedded reflections at the top (upper diatreme). The crater-shaped volcanoes are often circled by moderate to high-amplitude reflections that likely represent material ejected by large

) craters and cones occur

**84**

*Illustrations of the architecture of small-volume cones and craters. (a) Schematic cross-section through a cinder cone adapted from Kereszturi and Németh [6]. (b) Seismic cross-section highlighting the general morphology and seismic response of a cinder cone and associated lava field buried offshore Taranaki Basin, New Zealand. Note the characteristic inward-dipping reflections towards the crater and the outward-dipping structure away from the vent zone. (c) Plan view spectral decomposition of the cinder cone taken from the Winnie 3D survey, Eromanga Basin, Australia, highlighting the cone-shaped morphology of the vent and associated extensive lava field [9]. (d) Horizon mapping of the top surface of the cinder cone shown in (c). (d) Cross-section through a maar-diatreme adapted from Kereszturi and Németh [6]. (f) A seismic line across a maar-diatreme volcano buried in the offshore Banks Peninsula, New Zealand [22]. The chaotic reflections indicate deep excavations of the pre-eruptive subsurface. (g) Plan view spectral decomposition of a maar-diatreme buried in the Eromanga Basin, Australia [9]. (h) Oblique, TWT view of the proposed maar-diatreme in (g).*

The deduction of mounds- and crater-shaped seismic anomalies being igneous in origin can be reinforced by the presence of artefacts such as pull-up of seismic velocities (**Figure 6a**), indicating that rocks within the anomalies have a much higher acoustic velocity than the surrounding strata [25, 35]. In addition, doming of reflectors overlying mound-shaped volcanoes (**Figure 8a**) is common where

volcanic rocks are less compacted than surrounding sedimentary strata [59, 63]. Seismic interpretation shows that clusters of small craters and cones are often located above the tips of saucer-shaped intrusions or associated with high-amplitude reflections emplaced into pre-eruptive strata (**Figures 6, 8** and **10**), which suggest that magma is likely to stall in numerous interconnected batches immediately below volcanic fields [43, 89]. Multiple craters and cones have been interpreted to form hydrothermal vent complexes where shallow intrusions were emplaced within sedimentary strata [59, 110]. If the magma intrudes into organic-rich sedimentary sequences, these vent complexes could release large amounts of greenhouse gases from metamorphic aureoles, potentially triggering global warming events such as the Paleocene-Eocene Thermal Maximum; PETM [108, 111].

### **4.3 Large composite, shield and caldera volcanoes**

Large (i.e. >5 km3 ) composite, shield and caldera volcanoes are discrete landforms constructed over tens to millions of years by repeated eruptions at a relatively confined vent site [7]. The most distinctive large volcanoes are cone-shaped stratovolcanoes, overlapping compound edifices, low-profile shield volcanoes, and ring-shaped caldera depressions. Typically formed by polygenetic building mechanisms, these large volcanoes represent end-member variants with a broad spectrum of intermediary elements. The range of morphologies of polygenetic volcanoes can overlap with each other through time, complicating development of empirical models for interpreting the factors controlling their edifice growth mechanisms and evolution [112]. Each of these large volcanic landforms can be constructed from magmas of any known chemical composition and in all known tectonic settings [72].

Conversely, some particular morphologies are more likely to be developed in specific tectonic conditions and under the influence of certain magmas, allowing us to recognise generalities for each volcanic type. For example, andesitic-dacitic composite volcanoes are commonly derived from partial melting of the asthenosphere at subduction zones, often erupting along volcanic arcs such as the Andes in South America and the Cascades in western USA [5]. The viscosity of andesitic-dacitic magmas favours accumulation of lava and tephra near the eruptive site, building composite morphologies such as stratovolcanoes (e.g. Mt. Fuji, Japan) and compound volcanoes (e.g. Mt. Tongariro, New Zealand). Stratovolcanoes display large (ca 2 km high and 15 km wide) steep-sided (up to 30° slopes) flanks located next to a relatively stationary central vent (**Figure 11**). Whereas, compound volcanoes are formed by several overlapping edifices that together shape a distinctive massif of volcanic rocks separated from other adjacent volcanoes (**Figure 12**). Both stratoand compound volcanoes typically comprise accumulations of interbedded lavaflows, pyroclastic material and reworked volcanic debris [113]. Primary volcanic and epiclastic accumulations follow a proximal-distal facies pattern in which thick, amalgamated and coarser-grained layers are deposited close to the vent zone, while thin, tabular and fine-grained facies accumulate distally to the vent (**Figure 7**). The overall architecture of a composite volcano comprises a central vent zone and overlapping flanks circled by a radial ring-plain deposited around an individual edifice or a group of edifices. In addition, the flanks of composite volcanoes often contain small parasitic cinder cones and lava domes [114].

Shield volcanoes are typical products of low viscosity basaltic lavas erupted at intraplate hotspots, generally associated with extensional settings such as the Hawaiian volcanoes [115]. However, shield volcanoes are also commonly found along intracontinental rifts (e. g. Dama Ali, eastern Ethiopia) and subductionrelated volcanic arcs (e.g. Payun Matru, Argentina). Basaltic shield volcanoes consist of a central summit vent (which may or may not include a caldera), enclosed

**87**

by low-angle (<10°

*across the Kora volcano.*

**Figure 11.**

large amounts of fragmented material [117].

*Seismic and outcrop examples of large (>5 km3*

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins*

slopes) peripheral flanks, and a flat lava apron that can extend

*) composite volcanos. This type of volcanic landform typically* 

tens of km's from the vent [116]. Parasitic vents commonly erupt on the flanks of shield volcanoes, often forming rows of spatter and scoria cones aligned with normal faults (**Figure 13**). In addition, oceanic and paralic shield volcanoes are likely to contain a hyaloclastite apron and associated lava-deltas, in which interaction between lava and seawater may trigger hydrovolcanic explosions that can produce

*constitutes a single cone-shaped body with a central vent located at or near the summit of the volcano. (a and b) 3D perspective of a rendered amplitude seismic cube across the Kora volcano, New Zealand. (c and d) View of the north flank of the Taranaki volcano, New Zealand. Note the disrupted and channelised geometry of proximal deposits, while distal deposits typically are lobate and more continuous. In (b), the high-amplitude reflections (red) are discontinuous and disrupted, which likely reflect multiple depositional and erosional events, such as observed to form at the flanks of Taranaki volcano (d). (e) Oblique 3D view of the intrusive and extrusive parts of the Kora volcano. The edifice is highlighted by an opacity rendered amplitude cube, while the plumbing system was mapped as numerous interconnected geobodies. (f) Amplitude display of a seismic section* 

*DOI: http://dx.doi.org/10.5772/intechopen.95282*

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins DOI: http://dx.doi.org/10.5772/intechopen.95282*

### **Figure 11.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

the Paleocene-Eocene Thermal Maximum; PETM [108, 111].

**4.3 Large composite, shield and caldera volcanoes**

(ca 2 km high and 15 km wide) steep-sided (up to 30°

contain small parasitic cinder cones and lava domes [114].

Large (i.e. >5 km3

volcanic rocks are less compacted than surrounding sedimentary strata [59, 63]. Seismic interpretation shows that clusters of small craters and cones are often located above the tips of saucer-shaped intrusions or associated with high-amplitude reflections emplaced into pre-eruptive strata (**Figures 6, 8** and **10**), which suggest that magma is likely to stall in numerous interconnected batches immediately below volcanic fields [43, 89]. Multiple craters and cones have been interpreted to form hydrothermal vent complexes where shallow intrusions were emplaced within sedimentary strata [59, 110]. If the magma intrudes into organic-rich sedimentary sequences, these vent complexes could release large amounts of greenhouse gases from metamorphic aureoles, potentially triggering global warming events such as

constructed over tens to millions of years by repeated eruptions at a relatively confined vent site [7]. The most distinctive large volcanoes are cone-shaped stratovolcanoes, overlapping compound edifices, low-profile shield volcanoes, and ring-shaped caldera depressions. Typically formed by polygenetic building mechanisms, these large volcanoes represent end-member variants with a broad spectrum of intermediary elements. The range of morphologies of polygenetic volcanoes can overlap with each other through time, complicating development of empirical models for interpreting the factors controlling their edifice growth mechanisms and evolution [112]. Each of these large volcanic landforms can be constructed from magmas of any

Conversely, some particular morphologies are more likely to be developed in specific tectonic conditions and under the influence of certain magmas, allowing us to recognise generalities for each volcanic type. For example, andesitic-dacitic composite volcanoes are commonly derived from partial melting of the asthenosphere at subduction zones, often erupting along volcanic arcs such as the Andes in South America and the Cascades in western USA [5]. The viscosity of andesitic-dacitic magmas favours accumulation of lava and tephra near the eruptive site, building composite morphologies such as stratovolcanoes (e.g. Mt. Fuji, Japan) and compound volcanoes (e.g. Mt. Tongariro, New Zealand). Stratovolcanoes display large

a relatively stationary central vent (**Figure 11**). Whereas, compound volcanoes are formed by several overlapping edifices that together shape a distinctive massif of volcanic rocks separated from other adjacent volcanoes (**Figure 12**). Both stratoand compound volcanoes typically comprise accumulations of interbedded lavaflows, pyroclastic material and reworked volcanic debris [113]. Primary volcanic and epiclastic accumulations follow a proximal-distal facies pattern in which thick, amalgamated and coarser-grained layers are deposited close to the vent zone, while thin, tabular and fine-grained facies accumulate distally to the vent (**Figure 7**). The overall architecture of a composite volcano comprises a central vent zone and overlapping flanks circled by a radial ring-plain deposited around an individual edifice or a group of edifices. In addition, the flanks of composite volcanoes often

Shield volcanoes are typical products of low viscosity basaltic lavas erupted at intraplate hotspots, generally associated with extensional settings such as the Hawaiian volcanoes [115]. However, shield volcanoes are also commonly found along intracontinental rifts (e. g. Dama Ali, eastern Ethiopia) and subductionrelated volcanic arcs (e.g. Payun Matru, Argentina). Basaltic shield volcanoes consist of a central summit vent (which may or may not include a caldera), enclosed

known chemical composition and in all known tectonic settings [72].

) composite, shield and caldera volcanoes are discrete landforms

slopes) flanks located next to

**86**

*Seismic and outcrop examples of large (>5 km3 ) composite volcanos. This type of volcanic landform typically constitutes a single cone-shaped body with a central vent located at or near the summit of the volcano. (a and b) 3D perspective of a rendered amplitude seismic cube across the Kora volcano, New Zealand. (c and d) View of the north flank of the Taranaki volcano, New Zealand. Note the disrupted and channelised geometry of proximal deposits, while distal deposits typically are lobate and more continuous. In (b), the high-amplitude reflections (red) are discontinuous and disrupted, which likely reflect multiple depositional and erosional events, such as observed to form at the flanks of Taranaki volcano (d). (e) Oblique 3D view of the intrusive and extrusive parts of the Kora volcano. The edifice is highlighted by an opacity rendered amplitude cube, while the plumbing system was mapped as numerous interconnected geobodies. (f) Amplitude display of a seismic section across the Kora volcano.*

by low-angle (<10° slopes) peripheral flanks, and a flat lava apron that can extend tens of km's from the vent [116]. Parasitic vents commonly erupt on the flanks of shield volcanoes, often forming rows of spatter and scoria cones aligned with normal faults (**Figure 13**). In addition, oceanic and paralic shield volcanoes are likely to contain a hyaloclastite apron and associated lava-deltas, in which interaction between lava and seawater may trigger hydrovolcanic explosions that can produce large amounts of fragmented material [117].

### **Figure 12.**

*Seismic and outcrop examples of large (>5 km3 ) compound volcanoes. Several overlapping vents which are typically randomly distributed characterise this type of volcanic landform. (a) An aerial view of the southern sector of the Tongariro compound volcano with the Ruapehu stratovolcano in the background. (b) Plain view over a rendered amplitude seismic cube showing the location of three main vents within the Parihaka compound volcano, New Zealand. (c) Amplitude display of a seismic section across the Parihaka volcanoes. Note the overlapping flanks of the main vents. (d) Photograph from the summit of the Ngauruhoe volcano showing a detailed view of the Red Crater, Blue Lake Crater and overlapping lavas of the Mangahouhounui Fm, Tongariro compound volcano. (e) Detail of the amplitude display of a seismic section shown in (c). Note the overlapping reflections on the flanks of the vents.*

Large polygenetic volcanoes have been interpreted from seismic reflection datasets since the 1980s' in many sedimentary basins globally. Similar to their smaller cone and crater equivalents (Section 4.2), the reflection configuration within and around large buried volcanoes may make it possible to interpret their broad architecture and genesis. Buried composite and shield volcanoes typically resemble small mound- and cone-shaped vents (**Figures 10**–**13**). Therefore, their architecture comprises chaotic and inward-dipping reflections at the vent zone, continuous to discontinuous reflections at the flanks, and a wide, almost flat ring plain evident by high-to-moderated amplitude reflections that pinch and fade with increasing

**89**

**Figure 13.**

*the lava flow in (e).*

"balloon-and-straw" model [24, 28, 118].

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins*

distance from the main volcanic body [1, 63]. Parasitic and satellite vents are often described on the flanks of these large buried volcanoes, typically located above preexisting structures of the basement or at radial normal faults [52]. Interpretation of seismic reflection datasets suggests that the shallow (<5 km) plumbing system of large polygenetic volcanoes comprises a myriad of interconnected intrusive bodies, mainly aligned with crustal structures, markedly contrasting with the classic

*Seismic and outcrop examples of shield volcanoes with a central caldera. (a) Photograph of the northern flank of the Payun Matru Volcano, Argentina. (b) Amplitude display of a seismic section across the Barque volcano, offshore Canterbury Basin, New Zealand (Modified from [28]). (c) Aerial view of the region of the Payun Matru, a shield with a central caldera, and Payun Liso a stratovolcano. Note the NW alignment of cinder cones. (d) Plain view of a decomposed seismic cube showing the flanks and central depression of the Barque volcano. Parasitic and satellite vents are commonly aligned with normal faults. (e) Plain view of an RMS seismic cube across a lava flow of the Barque volcano. (f and g) Amplitude display of a seismic section across* 

*DOI: http://dx.doi.org/10.5772/intechopen.95282*

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins DOI: http://dx.doi.org/10.5772/intechopen.95282*

### **Figure 13.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

Large polygenetic volcanoes have been interpreted from seismic reflection datasets since the 1980s' in many sedimentary basins globally. Similar to their smaller cone and crater equivalents (Section 4.2), the reflection configuration within and around large buried volcanoes may make it possible to interpret their broad architecture and genesis. Buried composite and shield volcanoes typically resemble small mound- and cone-shaped vents (**Figures 10**–**13**). Therefore, their architecture comprises chaotic and inward-dipping reflections at the vent zone, continuous to discontinuous reflections at the flanks, and a wide, almost flat ring plain evident by high-to-moderated amplitude reflections that pinch and fade with increasing

*typically randomly distributed characterise this type of volcanic landform. (a) An aerial view of the southern sector of the Tongariro compound volcano with the Ruapehu stratovolcano in the background. (b) Plain view over a rendered amplitude seismic cube showing the location of three main vents within the Parihaka compound volcano, New Zealand. (c) Amplitude display of a seismic section across the Parihaka volcanoes. Note the overlapping flanks of the main vents. (d) Photograph from the summit of the Ngauruhoe volcano showing a detailed view of the Red Crater, Blue Lake Crater and overlapping lavas of the Mangahouhounui Fm, Tongariro compound volcano. (e) Detail of the amplitude display of a seismic section shown in (c). Note* 

*) compound volcanoes. Several overlapping vents which are* 

**88**

**Figure 12.**

*Seismic and outcrop examples of large (>5 km3*

*the overlapping reflections on the flanks of the vents.*

*Seismic and outcrop examples of shield volcanoes with a central caldera. (a) Photograph of the northern flank of the Payun Matru Volcano, Argentina. (b) Amplitude display of a seismic section across the Barque volcano, offshore Canterbury Basin, New Zealand (Modified from [28]). (c) Aerial view of the region of the Payun Matru, a shield with a central caldera, and Payun Liso a stratovolcano. Note the NW alignment of cinder cones. (d) Plain view of a decomposed seismic cube showing the flanks and central depression of the Barque volcano. Parasitic and satellite vents are commonly aligned with normal faults. (e) Plain view of an RMS seismic cube across a lava flow of the Barque volcano. (f and g) Amplitude display of a seismic section across the lava flow in (e).*

distance from the main volcanic body [1, 63]. Parasitic and satellite vents are often described on the flanks of these large buried volcanoes, typically located above preexisting structures of the basement or at radial normal faults [52]. Interpretation of seismic reflection datasets suggests that the shallow (<5 km) plumbing system of large polygenetic volcanoes comprises a myriad of interconnected intrusive bodies, mainly aligned with crustal structures, markedly contrasting with the classic "balloon-and-straw" model [24, 28, 118].

### **Figure 14.**

*Seismic and outcrop examples of shield volcanoes with a central caldera. (a) Uninterpreted and (b) interpreted amplitude display of a seismic section across the Hades caldera, offshore Deepwater Taranaki Basin, New Zealand (Modified from [28]). (c) Post-eruptive surface and (d) pre-eruptive surface isochron horizon maps of the Hades caldera. Note the wide (ca 5 km) central depression with inward-dipping reflections circled by a ring of outward-dipping layered material. (e) Pre-eruptive surface isochron horizon map applying an edge-detection attribute, which is enhancing a series of ring-shaped faults at the location of the caldera depression. (f) Photograph of the crater lake at the summit of the Changbaishan Volcano, Chinese and North Korean border. The lake marks the location of a 5 km wide caldera vent formed by a large pyroclastic eruption in 946 AD. Note the steeply inclined outward-dipping layers of white ignimbrite rocks at the left corner of the picture.*

Caldera-forming volcanoes are commonly associated with subsidence and collapse of the roof of magma chambers due to partial withdrawal of magma during voluminous and short-lived eruptions [119]. Characteristic caldera volcanoes are silicic in composition and produced by ultra-Plinian eruptions, often developing in association with rifted arcs such as the Taupo Volcanic Zone in New Zealand [120, 121]. However, smaller pyroclastic and non-explosive calderas of more mafic compositions often form within the central vent zone of composite and shield volcanoes [122]. Caldera volcanoes have a variety of geometries and structures mainly defined by mechanisms of pyroclastic material dispersal, caldera collapse,

**91**

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins*

and dome resurgence [123]. The general architecture of large silicic calderas comprises a central depression of 1–2 km depth surrounded by lateral by an ignimbrite plateau or steepen flanks of pyroclastic and lava material, which can cover areas of

thick sequences of intra-caldera pyroclastic deposits, late-stage andesitic-rhyolitic lava-flows and domes, lacustrine sediments and debris. Caldera volcanoes may or may not produce a post-eruptive resurgent dome, a consequence of intra-caldera uplift from a renewed rise of magma into the chamber(s), such as documented from

Interpretation of buried caldera volcanoes from seismic data is scarce, and to our knowledge, only documented in two places offshore New Zealand [28]. Barque volcano, offshore Canterbury Basin, is potentially a large (ca 20 km wide) shield volcano with a central caldera (**Figure 13**). Hades caldera, in the Deepwater Taranaki, has a semi-circular structure 10 km across with a central depression 3.5 km wide and 1 km deep bounded by ring faults, likely formed by pyroclastic mechanisms of material fragmentation and dispersion (**Figure 14**). Both examples show no evidence of a single large batch of magma sited beneath the caldera. Rather, multiple interconnected intrusions, including saucer-shaped sills and tabular bodies aligned with pre-and syn-rift faults more likely describe their magma plumbing systems

with continental break-up and upwelling of mantle plumes that form Large Igneous Provinces (LIPs). Characteristically, LIPs comprise extensive flood basalt plateaus derived from decompression melting of the mantle, but more differentiated alkalic, tholeiitic, and silicic rocks can also occur as lavas, pyroclastic, and intrusive bodies [125]. LIPs constitute the most extensive volcanic landscapes on Earth, including regional-scale igneous-dominated structures such as continental flood basalts, volcanic rifted margins, oceanic plateaus, submarine ridges, seamount chains, and ocean-basin flood basalts [126]. The voluminous lava fields often erupt at both continental (e.g. Siberian Traps, Asia) and oceanic crust (e.g. Ontong Java Plateau, Pacific Ocean), as well as at divergent plate boundaries such as the South Atlantic

The broad architecture of LIPs consists of stacks of sub-horizontal sheets of lava flows up to ca 10 km thick underlying by networks of subvolcanic sills and dykes [51, 128]. The extrusive part of LIPs is interpreted to be mainly fed by repeated voluminous eruptions sourced from scattered fissure vents and shield volcanoes, in which the entire volcanic pile is typically constructed in relatively short time spans (<1 Myr).

kilometres from the vent site, such as described in the Columbia River Plateau and the Deccan Traps [72]. The Laki eruption in Iceland, for example, is one of the larg-

Most voluminous lava fields are interbedded with sedimentary basins formed by crustal extension, rifting, and continental drifting [130]. Volcanic rift margins have been the most intensively studied LIPs from seismic reflection datasets (**Figure 15**). Over the past 40 years, interpretation of enormous amounts of seismic data along the boundaries of the Atlantic, Western Australian, and Southern Indian continental crusts showed that rift margins typically comprise a set of characteristic volcanic seismic facies units [4, 11, 131]. These seismic facies units represent interactions between

est documented historical lava flows. It covered an area of near 600 km2

long fissure vent system consisting of scoria, spatter, and tuff cones [129].

Iceland in the 1780s, with an estimated discharge of almost 15 km3

) lava fields are commonly associated

and extend for hundreds of

of southern

of lava from a 27 km

[72]. The central depression is often bounded by ring faults and hosts

*DOI: http://dx.doi.org/10.5772/intechopen.95282*

the Toba Volcano, Indonesia, and Yellowstone, USA [124].

>3000 km2

(**Figures 13** and **14**).

Margins [127].

**4.4 Voluminous lava fields**

Eruptions of voluminous (i.e. >10,000 km3

Individual flows can reach volumes as much as 1000 km3

### *Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins DOI: http://dx.doi.org/10.5772/intechopen.95282*

and dome resurgence [123]. The general architecture of large silicic calderas comprises a central depression of 1–2 km depth surrounded by lateral by an ignimbrite plateau or steepen flanks of pyroclastic and lava material, which can cover areas of >3000 km2 [72]. The central depression is often bounded by ring faults and hosts thick sequences of intra-caldera pyroclastic deposits, late-stage andesitic-rhyolitic lava-flows and domes, lacustrine sediments and debris. Caldera volcanoes may or may not produce a post-eruptive resurgent dome, a consequence of intra-caldera uplift from a renewed rise of magma into the chamber(s), such as documented from the Toba Volcano, Indonesia, and Yellowstone, USA [124].

Interpretation of buried caldera volcanoes from seismic data is scarce, and to our knowledge, only documented in two places offshore New Zealand [28]. Barque volcano, offshore Canterbury Basin, is potentially a large (ca 20 km wide) shield volcano with a central caldera (**Figure 13**). Hades caldera, in the Deepwater Taranaki, has a semi-circular structure 10 km across with a central depression 3.5 km wide and 1 km deep bounded by ring faults, likely formed by pyroclastic mechanisms of material fragmentation and dispersion (**Figure 14**). Both examples show no evidence of a single large batch of magma sited beneath the caldera. Rather, multiple interconnected intrusions, including saucer-shaped sills and tabular bodies aligned with pre-and syn-rift faults more likely describe their magma plumbing systems (**Figures 13** and **14**).

### **4.4 Voluminous lava fields**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

Caldera-forming volcanoes are commonly associated with subsidence and collapse of the roof of magma chambers due to partial withdrawal of magma during voluminous and short-lived eruptions [119]. Characteristic caldera volcanoes are silicic in composition and produced by ultra-Plinian eruptions, often developing in association with rifted arcs such as the Taupo Volcanic Zone in New Zealand [120, 121]. However, smaller pyroclastic and non-explosive calderas of more mafic compositions often form within the central vent zone of composite and shield volcanoes [122]. Caldera volcanoes have a variety of geometries and structures mainly defined by mechanisms of pyroclastic material dispersal, caldera collapse,

*Seismic and outcrop examples of shield volcanoes with a central caldera. (a) Uninterpreted and (b) interpreted amplitude display of a seismic section across the Hades caldera, offshore Deepwater Taranaki Basin, New Zealand (Modified from [28]). (c) Post-eruptive surface and (d) pre-eruptive surface isochron horizon maps of the Hades caldera. Note the wide (ca 5 km) central depression with inward-dipping reflections circled by a ring of outward-dipping layered material. (e) Pre-eruptive surface isochron horizon map applying an edge-detection attribute, which is enhancing a series of ring-shaped faults at the location of the caldera depression. (f) Photograph of the crater lake at the summit of the Changbaishan Volcano, Chinese and North Korean border. The lake marks the location of a 5 km wide caldera vent formed by a large pyroclastic eruption in 946 AD. Note the steeply inclined outward-dipping layers of white ignimbrite rocks at the left corner of the* 

**90**

**Figure 14.**

*picture.*

Eruptions of voluminous (i.e. >10,000 km3 ) lava fields are commonly associated with continental break-up and upwelling of mantle plumes that form Large Igneous Provinces (LIPs). Characteristically, LIPs comprise extensive flood basalt plateaus derived from decompression melting of the mantle, but more differentiated alkalic, tholeiitic, and silicic rocks can also occur as lavas, pyroclastic, and intrusive bodies [125]. LIPs constitute the most extensive volcanic landscapes on Earth, including regional-scale igneous-dominated structures such as continental flood basalts, volcanic rifted margins, oceanic plateaus, submarine ridges, seamount chains, and ocean-basin flood basalts [126]. The voluminous lava fields often erupt at both continental (e.g. Siberian Traps, Asia) and oceanic crust (e.g. Ontong Java Plateau, Pacific Ocean), as well as at divergent plate boundaries such as the South Atlantic Margins [127].

The broad architecture of LIPs consists of stacks of sub-horizontal sheets of lava flows up to ca 10 km thick underlying by networks of subvolcanic sills and dykes [51, 128]. The extrusive part of LIPs is interpreted to be mainly fed by repeated voluminous eruptions sourced from scattered fissure vents and shield volcanoes, in which the entire volcanic pile is typically constructed in relatively short time spans (<1 Myr). Individual flows can reach volumes as much as 1000 km3 and extend for hundreds of kilometres from the vent site, such as described in the Columbia River Plateau and the Deccan Traps [72]. The Laki eruption in Iceland, for example, is one of the largest documented historical lava flows. It covered an area of near 600 km2 of southern Iceland in the 1780s, with an estimated discharge of almost 15 km3 of lava from a 27 km long fissure vent system consisting of scoria, spatter, and tuff cones [129].

Most voluminous lava fields are interbedded with sedimentary basins formed by crustal extension, rifting, and continental drifting [130]. Volcanic rift margins have been the most intensively studied LIPs from seismic reflection datasets (**Figure 15**). Over the past 40 years, interpretation of enormous amounts of seismic data along the boundaries of the Atlantic, Western Australian, and Southern Indian continental crusts showed that rift margins typically comprise a set of characteristic volcanic seismic facies units [4, 11, 131]. These seismic facies units represent interactions between

### **Figure 15.**

*Seismic and outcrop examples of volcanic rift margins and lava-fields. (a) Amplitude display of a seismic section across the Kolga Lava Delta, offshore Norway, showing the characteristic wedge of progradational deltas (From [45]). (b) Prograding foresets of a lava delta in western Greenland. (c) Perspective view of the top-basalt horizon of the Vøring Escarpment, offshore Norway (From [29]). (d) Lava field and escarpments formed during the 2018 series of eruptions of the Kilauea Volcano, Hawaii. (e) Perspective view of the Vøring Escarpment (From [29]). (f) Geometric relationship of intrusive and extrusive bodies of a voluminous lava field in western Greenland. Data courtesy of TGS (a).*

volcanism and sedimentation, and their interpretation informs the construction of models for the initiation and evolution of volcanic rift margins [26]. The typical volcanic rift margin sequence initiates with aggradation of peperites, hydrobreccias, and pillow-lavas where magma interacts with water and wet sediments, while subaerial lava-flows can develop at the basin margins and on topographic highs [132]. Continued aggradation and progradation of igneous material favours more effusive and subaerial volcanism, in which eruptions tend to form extensive sheets of stacked lava-flow deposits [34]. If the lava-flows stretch an existing shoreline, a prograding lava-delta comprising of hyaloclastic and epiclastic material can be developed [133]. Subsequently, these volcanic deposits may be exposed to erosional conditions, forming escarpments surfaces, slumps, and volcaniclastic gravity flow deposits triggered by degradation of the volcanic sequence [134].

A recent seismic geomorphological study used a 2500 km<sup>2</sup> high-quality 3D seismic survey to image the top-basalt horizon of the Vøring Marginal High, offshore Norway [29]. Interpretation of this seismic horizon revealed a series of volcanic macroforms such as lava-flows with compressional ridges and braided lava-channels

**93**

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins*

with similar structure and size of morphologies described in modern subaerial lava fields (**Figure 15**). In addition, the Vøring Marginal High 3D data showed numerous pitted and irregular lava surfaces next to smooth sheet-like reflections with geometry comparable to fields of small cone and crater volcanoes and their associated peripheral lava flows. These pitted seismic features are interpreted to correspond to places where magma was emplaced into wet sediments or water [29]. Debris flows deposits along with large slumped blocks are well imaged at the top of the Vøring Escarpment, revealing a volcanic morphology influenced by erosion and degrada-

Interpretation of 2D and 3D seismic reflection datasets provides valuable insights into the morphology and stratigraphic signature of entire igneous systems buried in sedimentary basins. The application of 3D seismic visualisation methods offers a unique opportunity for direct comparison of the geomorphic aspects of buried and outcropping volcanoes, with resolutions down to tens of metres.

Buried volcanic systems comprise a network of intrusive, eruptive, and sedimen-

Description and interpretation of seismic reflection surveys together with their outcropping volcano analogues from key localities worldwide suggest three main geomorphic categories of buried volcanoes. These categories are (1) clusters of

spatter cones, scoria cones, tuff cones, and hydrothermal vent complexes, (2) large

size, and spatio-temporal distribution of eruptive centres, and is independent of parameters such as magma composition, tectonic setting, or environment where the eruption occurred. Classifying the buried volcanoes into geomorphic categories helps us to understand the processes that link their endogenous and exogenous realms, providing insights into the architecture, edifice growth mechanisms and

The modern methods of seismic interpretation, from 2D regional scale to detailed 3D analysis, can provide an accurate understanding of the geological processes that formed the volcanoes now buried in the subsurface. Realistic models for the facies distribution and architecture of buried volcanoes can be constrained by their geomorphic similarities to outcropping volcanoes, establishing the principles

We would like to thank the Ministry of Business, Innovation and Employment (MBIE) of New Zealand and TGS for access to seismic and well data, and IHS

longevity of igneous systems buried in sedimentary basins.

for the new discipline of seismic-reflection volcanology.

) composite, shield and caldera volcanoes, and (3) voluminous lava fields

). This classification of buried volcanoes is based on their geometry,

from both seismic and outcrop analyses. These architectural elements often show a spatial and temporal distribution controlled by their distance from eruptive centres. The geometry and internal arrangement of facies within these elements reflect a range of physical factors including, magma composition, effusion discharge rate, degree of material fragmentation, and the presence or absence of water at the eruption vent. Many, if not most, volcanic systems are underlain by shallow (<5 km) interconnected networks of sills, saucer-sills, laccoliths, dykes, and hybrid intrusions that often align with pre-existing crustal structures or contemporaneous faults.

–104

) craters and cones, including maar-diatremes, tuff rings,

meters that are recognisable

*DOI: http://dx.doi.org/10.5772/intechopen.95282*

**5. Conclusions**

small-volume (<1 km3

**Acknowledgements**

(>5 km3

(>10,000 km3

tion of pre-existing voluminous lava fields (**Figure 15**).

tary architectural elements with length scales of 102

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins DOI: http://dx.doi.org/10.5772/intechopen.95282*

with similar structure and size of morphologies described in modern subaerial lava fields (**Figure 15**). In addition, the Vøring Marginal High 3D data showed numerous pitted and irregular lava surfaces next to smooth sheet-like reflections with geometry comparable to fields of small cone and crater volcanoes and their associated peripheral lava flows. These pitted seismic features are interpreted to correspond to places where magma was emplaced into wet sediments or water [29]. Debris flows deposits along with large slumped blocks are well imaged at the top of the Vøring Escarpment, revealing a volcanic morphology influenced by erosion and degradation of pre-existing voluminous lava fields (**Figure 15**).

## **5. Conclusions**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

volcanism and sedimentation, and their interpretation informs the construction of models for the initiation and evolution of volcanic rift margins [26]. The typical volcanic rift margin sequence initiates with aggradation of peperites, hydrobreccias, and pillow-lavas where magma interacts with water and wet sediments, while subaerial lava-flows can develop at the basin margins and on topographic highs [132]. Continued aggradation and progradation of igneous material favours more effusive and subaerial volcanism, in which eruptions tend to form extensive sheets of stacked lava-flow deposits [34]. If the lava-flows stretch an existing shoreline, a prograding lava-delta comprising of hyaloclastic and epiclastic material can be developed [133]. Subsequently, these volcanic deposits may be exposed to erosional conditions, forming escarpments surfaces, slumps, and volcaniclastic gravity flow deposits triggered

*Seismic and outcrop examples of volcanic rift margins and lava-fields. (a) Amplitude display of a seismic section across the Kolga Lava Delta, offshore Norway, showing the characteristic wedge of progradational deltas (From [45]). (b) Prograding foresets of a lava delta in western Greenland. (c) Perspective view of the top-basalt horizon of the Vøring Escarpment, offshore Norway (From [29]). (d) Lava field and escarpments formed during the 2018 series of eruptions of the Kilauea Volcano, Hawaii. (e) Perspective view of the Vøring Escarpment (From [29]). (f) Geometric relationship of intrusive and extrusive bodies of a voluminous lava* 

mic survey to image the top-basalt horizon of the Vøring Marginal High, offshore Norway [29]. Interpretation of this seismic horizon revealed a series of volcanic macroforms such as lava-flows with compressional ridges and braided lava-channels

high-quality 3D seis-

by degradation of the volcanic sequence [134].

*field in western Greenland. Data courtesy of TGS (a).*

A recent seismic geomorphological study used a 2500 km<sup>2</sup>

**92**

**Figure 15.**

Interpretation of 2D and 3D seismic reflection datasets provides valuable insights into the morphology and stratigraphic signature of entire igneous systems buried in sedimentary basins. The application of 3D seismic visualisation methods offers a unique opportunity for direct comparison of the geomorphic aspects of buried and outcropping volcanoes, with resolutions down to tens of metres.

Buried volcanic systems comprise a network of intrusive, eruptive, and sedimentary architectural elements with length scales of 102 –104 meters that are recognisable from both seismic and outcrop analyses. These architectural elements often show a spatial and temporal distribution controlled by their distance from eruptive centres. The geometry and internal arrangement of facies within these elements reflect a range of physical factors including, magma composition, effusion discharge rate, degree of material fragmentation, and the presence or absence of water at the eruption vent. Many, if not most, volcanic systems are underlain by shallow (<5 km) interconnected networks of sills, saucer-sills, laccoliths, dykes, and hybrid intrusions that often align with pre-existing crustal structures or contemporaneous faults.

Description and interpretation of seismic reflection surveys together with their outcropping volcano analogues from key localities worldwide suggest three main geomorphic categories of buried volcanoes. These categories are (1) clusters of small-volume (<1 km3 ) craters and cones, including maar-diatremes, tuff rings, spatter cones, scoria cones, tuff cones, and hydrothermal vent complexes, (2) large (>5 km3 ) composite, shield and caldera volcanoes, and (3) voluminous lava fields (>10,000 km3 ). This classification of buried volcanoes is based on their geometry, size, and spatio-temporal distribution of eruptive centres, and is independent of parameters such as magma composition, tectonic setting, or environment where the eruption occurred. Classifying the buried volcanoes into geomorphic categories helps us to understand the processes that link their endogenous and exogenous realms, providing insights into the architecture, edifice growth mechanisms and longevity of igneous systems buried in sedimentary basins.

The modern methods of seismic interpretation, from 2D regional scale to detailed 3D analysis, can provide an accurate understanding of the geological processes that formed the volcanoes now buried in the subsurface. Realistic models for the facies distribution and architecture of buried volcanoes can be constrained by their geomorphic similarities to outcropping volcanoes, establishing the principles for the new discipline of seismic-reflection volcanology.

### **Acknowledgements**

We would like to thank the Ministry of Business, Innovation and Employment (MBIE) of New Zealand and TGS for access to seismic and well data, and IHS

Markit and Schlumberger for providing academic licence to use Kingdom and Petrel software. AB thanks funding from the MBIE research grant UOCX1707. SP acknowledges support from the Norwegian Research Council Centres of Excellence funding scheme (CEED; project number 223272). We appreciate the constructive reviews of Ray Cas and Jim Cole, and the contribution of Jessica Fensom in proofreading and discussing the manuscript.
