**Abstract**

Across the globe, volcanoes and volcanic terrains present one of the most complex geological systems on Earth that, depending on magma type, viscosity, and water and gas content, form a diverse range of products in terms of geomorphology, lithologic suites, structures, and stratigraphy. In broad terms, magmas, with their diagnostic composition, derive from specific tectonic settings, *e.g.*, basalt-dominated oceanic crusts, acidic magma from continental plates, and andesitic convergent-plate margins. In addition to magma composition and volcanic rock types, there is a wide range of volcanic products, manifest at all scales, dependent on how magma interacts with the Earth's surface, varying, for instance, from lava flows such as vesicular lava beds and flow-banded to flow-laminated lava beds, to breccias, tephra (ejecta) deposits, and bombs, amongst others, each commonly with their diagnostic small-scale lithological/structural features. This wealth of rock types, stratigraphy, and structures linked to geologic setting, potentially has geoheritage significance, and we provide here methods tailored for volcanoes and volcanic rocks of identifying, classifying and evaluating the complex and heterogeneous nature of volcanoes so that the full complement of their geology for a given region can be appreciated and incorporated into thematic geoparks, Nature Reserves and protected areas. For sites of geoheritage significance, we present (1) a globally-applicable Geoheritage Tool-kit to systematically identify volcanic geoheritage sites, (2) a technique to classify/categorise geoheritage sites, and (3) a semiquantitative method to evaluate the geoheritage significance of volcanic sites.

**Keywords:** volcanoes, volcanic geology, geoheritage, geoconservation, geoparks

### **1. Introduction**

Volcanoes and volcanic terrains are one of the most complex geological systems on Earth forming a range of products from the megascale and large scale to small scale that have varying geological significance. Of necessity, the ensuing text is a brief summary of a very complex and diverse subject matter, presented to a level sufficient to convey their comparative diversity and scale of expression for purposes of geoheritage and geoconservation. More detailed and comprehensive treatment of volcanoes can be found in various encyclopaedia and text books [1–13].

Magma composition is highly variable across volcanic terrains and at a single volcano, with attendant variation also in viscosity, gas content, water content, and behaviour of the erupted material. Magma can range in composition from basic (*e.g.*, basalt) to intermediate (*e.g.*, andesite) to acidic (*e.g.*, rhyolite, rhyodacite, dacite). Volcanoes extrude magmas in any of the Earth's surface environments though most are located at plate boundaries (terrestrial and submarine rift zones, subduction and collision zones, and transform zones); they can also extrude in intra-plate and cratonic settings. Commonly, magma composition is linked to global geological setting or to regional geological setting, with basaltic magmas (basic magmas) deriving from oceanic crusts, andesitic and associated magmas (intermediate magmas) deriving from collision between oceanic crust and continental crust, and a range of acidic magmas deriving from continental crusts. Continental crusts, with their lithological variability reflecting craton heterogeneity, metamorphic history, and sedimentary basin-filling, hold scope through melting, diffusion, and mixing to create a wider range of magma compositional types than ocean-crust-derived basic magmas. Thus, in continental situations, depending on geological setting, vertically-ascending magma plumbing or conduits that feed/supply volcanic eruptions can traverse variable crust types from cratons and Precambrian stratigraphic sequences to polylithic, stratified Phanerozoic sedimentary basins, to submarine seafloors. As such, in the process, this magma plumbing or conduits incorporate material from the host rocks they traverse via such processes as partial melting of host rocks, chemical diffusion from host rocks, and plucking and melting of solid fragments to form enclaves, xenoliths, and xenocrysts.

Volcanoes can erupt in a wide variety of environments, including relatively dry terrestrial environments, water-saturated terrestrial environments, continental edge, submarine environments, and from under ice (glaciers) and, thus, at the large scale, they can have a variety of lithologic/structural expression and a variety of geological structural and stratigraphic relationships to the host rocks that they intrude into or erupt from. Depending on a number of factors including gas content and contact with water, eruptions at one extreme can be extremely explosive (*e.g.*, phreatomagmatic eruptions where magma interfaces with groundwater; *cf*. Németh & Kósik [11]), sending tephra (various-sized pyroclastic material or ejecta such as lapilli and ash composed of rock fragments and glass), gas, and magma high up into the atmosphere (with some of the more explosive eruptions dispersing ash as plumes hundreds of kilometres from their eruptive source) or, at the other extreme, involve more quiescent effusive lava flows (for review see Németh & Kósik [11, 13]). The ejecta can be fine-grained ranging to fine-grained with or without included bombs, or can be dominated by coarse-grained to boulder-sized material and (depending on magma type, gas content, water, and geological setting) volcanic ash can be dominantly lithoclastic, or crystal-rich, or (volcanic glass) shard-rich, or mixtures of these [5].

Water and gas are important components of volcanism and play major roles in magma viscosity, development of vesicles, development of pumice, syn-eruption rain, post-eruption rain-storms, and moisture condensation effects. With an eruptive plume passing through a cloud, or volcano-associated rain-storms, or condensation of moisture within an expanding plume, there can be development of accretionary lapilli [14–16] and, with post-eruption rain and erosion, the potential for slurries of pyroclastic material, rocky debris and water (*e.g.*, lahars) which can

**331**

**Figure 1.**

*volcanoes).*

*Volcanoes: Identifying and Evaluating Their Significant Geoheritage Features from the Large…*

be erosive into the layered tephra, or can become interlayered with the volcanic

At the Earth's surface, at the large scale, volcanoes are expressed in a variety of geometric and stratigraphic arrays, *viz*., stratovolcanoes, shield volcanoes, and volcanic fissures leading to sheet flows, amongst others, with the geometry dependent on whether extrusive material, at one extreme, is tephra-dominated (mainly ash and lapilli) and built to relatively high relief (*e.g.*, cinder cones and stratovolcanoes) or, at the other extreme, lava-dominated and built to relatively low relief (*e.g.*, shield volcanoes and dome volcanoes), or intermediate with alternating tephra and lava layers and built to high relief (*e.g.*,

At the medium scale, there is an abundance of features expressed in volcanic extrusions, *e.g.*, layered lithologically-similar ash beds, layered lithologicallyheterogeneous ash beds, structureless lava beds, vesicular lava beds, flow-banded to flow-laminated lava beds, lava beds with spherulitic structures, pillows and their associated structures and mineralogy, deuteric minerals formed within lava pillows, layered ejecta deposits (ash beds), volcanic bombs, volcanic blocks, postsolidification polygonal jointing, mega-breccias and meso-breccias, micro-breccias, lava tunnels, mixing of magma types, formation of obsidian by the rapid cooling of magma to form glass, formation of pumice by super-heated, highly pressurized magma being violently erupted, diatremes and maars, secondary dykes, amongst

At the small scale, there is deformation of ash-bed layering/lamination by bombs, flow-breccia structures, xenoliths and xenocrysts, surge structures, stalactitic and stalagmitic structures, lamination in obsidian, deformation (stretching) of vesicles of lava and pumice by flow, lapilli and accretionary

*The categories of sites of geoheritage significance (modified from Brocx & Semeniuk [1] and tailored for* 

*DOI: http://dx.doi.org/10.5772/intechopen.97928*

stratovolcanoes).

many others [6, 9, 10].

deposits all producing complex stratigraphy.

### *Volcanoes: Identifying and Evaluating Their Significant Geoheritage Features from the Large… DOI: http://dx.doi.org/10.5772/intechopen.97928*

be erosive into the layered tephra, or can become interlayered with the volcanic deposits all producing complex stratigraphy.

At the Earth's surface, at the large scale, volcanoes are expressed in a variety of geometric and stratigraphic arrays, *viz*., stratovolcanoes, shield volcanoes, and volcanic fissures leading to sheet flows, amongst others, with the geometry dependent on whether extrusive material, at one extreme, is tephra-dominated (mainly ash and lapilli) and built to relatively high relief (*e.g.*, cinder cones and stratovolcanoes) or, at the other extreme, lava-dominated and built to relatively low relief (*e.g.*, shield volcanoes and dome volcanoes), or intermediate with alternating tephra and lava layers and built to high relief (*e.g.*, stratovolcanoes).

At the medium scale, there is an abundance of features expressed in volcanic extrusions, *e.g.*, layered lithologically-similar ash beds, layered lithologicallyheterogeneous ash beds, structureless lava beds, vesicular lava beds, flow-banded to flow-laminated lava beds, lava beds with spherulitic structures, pillows and their associated structures and mineralogy, deuteric minerals formed within lava pillows, layered ejecta deposits (ash beds), volcanic bombs, volcanic blocks, postsolidification polygonal jointing, mega-breccias and meso-breccias, micro-breccias, lava tunnels, mixing of magma types, formation of obsidian by the rapid cooling of magma to form glass, formation of pumice by super-heated, highly pressurized magma being violently erupted, diatremes and maars, secondary dykes, amongst many others [6, 9, 10].

At the small scale, there is deformation of ash-bed layering/lamination by bombs, flow-breccia structures, xenoliths and xenocrysts, surge structures, stalactitic and stalagmitic structures, lamination in obsidian, deformation (stretching) of vesicles of lava and pumice by flow, lapilli and accretionary

**Figure 1.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

of geoheritage and geoconservation. More detailed and comprehensive treatment of

Magma composition is highly variable across volcanic terrains and at a single volcano, with attendant variation also in viscosity, gas content, water content, and behaviour of the erupted material. Magma can range in composition from basic (*e.g.*, basalt) to intermediate (*e.g.*, andesite) to acidic (*e.g.*, rhyolite, rhyodacite, dacite). Volcanoes extrude magmas in any of the Earth's surface environments though most are located at plate boundaries (terrestrial and submarine rift zones, subduction and collision zones, and transform zones); they can also extrude in intra-plate and cratonic settings. Commonly, magma composition is linked to global geological setting or to regional geological setting, with basaltic magmas (basic magmas) deriving from oceanic crusts, andesitic and associated magmas (intermediate magmas) deriving from collision between oceanic crust and continental crust, and a range of acidic magmas deriving from continental crusts. Continental crusts, with their lithological variability reflecting craton heterogeneity, metamorphic history, and sedimentary basin-filling, hold scope through melting, diffusion, and mixing to create a wider range of magma compositional types than ocean-crust-derived basic magmas. Thus, in continental situations, depending on geological setting, vertically-ascending magma plumbing or conduits that feed/supply volcanic eruptions can traverse variable crust types from cratons and Precambrian stratigraphic sequences to polylithic, stratified Phanerozoic sedimentary basins, to submarine seafloors. As such, in the process, this magma plumbing or conduits incorporate material from the host rocks they traverse via such processes as partial melting of host rocks, chemical diffusion from host rocks, and plucking and melting of solid fragments to form enclaves,

Volcanoes can erupt in a wide variety of environments, including relatively dry terrestrial environments, water-saturated terrestrial environments, continental edge, submarine environments, and from under ice (glaciers) and, thus, at the large scale, they can have a variety of lithologic/structural expression and a variety of geological structural and stratigraphic relationships to the host rocks that they intrude into or erupt from. Depending on a number of factors including gas content and contact with water, eruptions at one extreme can be extremely explosive (*e.g.*, phreatomagmatic eruptions where magma interfaces with groundwater; *cf*. Németh & Kósik [11]), sending tephra (various-sized pyroclastic material or ejecta such as lapilli and ash composed of rock fragments and glass), gas, and magma high up into the atmosphere (with some of the more explosive eruptions dispersing ash as plumes hundreds of kilometres from their eruptive source) or, at the other extreme, involve more quiescent effusive lava flows (for review see Németh & Kósik [11, 13]). The ejecta can be fine-grained ranging to fine-grained with or without included bombs, or can be dominated by coarse-grained to boulder-sized material and (depending on magma type, gas content, water, and geological setting) volcanic ash can be dominantly lithoclastic, or crystal-rich, or (volcanic glass) shard-rich, or mixtures of

Water and gas are important components of volcanism and play major roles in magma viscosity, development of vesicles, development of pumice, syn-eruption rain, post-eruption rain-storms, and moisture condensation effects. With an eruptive plume passing through a cloud, or volcano-associated rain-storms, or condensation of moisture within an expanding plume, there can be development of accretionary lapilli [14–16] and, with post-eruption rain and erosion, the potential for slurries of pyroclastic material, rocky debris and water (*e.g.*, lahars) which can

volcanoes can be found in various encyclopaedia and text books [1–13].

**330**

these [5].

xenoliths, and xenocrysts.

*The categories of sites of geoheritage significance (modified from Brocx & Semeniuk [1] and tailored for volcanoes).*

lapilli, a wide range of vesicle-lining or vesicle-filling minerals, crystal types and forms (*e.g.*, zeolites, calcite, quartz, chalcedony, epidote), mineral-filled fractures, small-scale fumarolic fissures or vents (empty, or filled with crystals, filled with massive lava, or filled with vesicular lava), alteration of the

### **Figure 2.**

*Following Brocx & Semeniuk [17], the four levels of significance recognised in this Chapter (modified from Brocx & Semeniuk [17, 18] and tailored for volcanoes): International, National, State-wide to Regional, and Local. Examples of many volcanoes and their deposits are included in this diagram.*

**333**

**Figure 4.**

*and sheet flows are not included.*

**Figure 3.**

*from Brocx & Semeniuk [17] and tailored for volcanoes).*

*Volcanoes: Identifying and Evaluating Their Significant Geoheritage Features from the Large…*

primary texture and mineralogy by interactions with either fluids within the magma (deuterism [or autometasomatism]) or by fluids in the near-surface

A selection of diagrams to illustrate the principles of Geoheritage and how to categorise volcanic sites and evaluate their significance are presented in **Figures 1**–**3**, and a series of photographic plates illustrating the variety of geometric, stratigraphic arrays, and lithology and mineralogy of volcanoes and volcanic geology are

*The Geoheritage Tool-kit used to systematically identify and assess sites of geoheritage significance (modified* 

*The variety of geometric and stratigraphic arrays of volcanoes,* viz*., cinder cones, composite (stratovolcanoes), lava cones, and shield volcanoes. This diagram emphasises the gradation from tephra-dominated to lavadominated eruptions and the corresponding changes in stratigraphy and form of the volcanoes. Fissure vents,* 

*DOI: http://dx.doi.org/10.5772/intechopen.97928*

environment.

presented in **Figures 4**–**8**.

*Volcanoes: Identifying and Evaluating Their Significant Geoheritage Features from the Large… DOI: http://dx.doi.org/10.5772/intechopen.97928*

primary texture and mineralogy by interactions with either fluids within the magma (deuterism [or autometasomatism]) or by fluids in the near-surface environment.

A selection of diagrams to illustrate the principles of Geoheritage and how to categorise volcanic sites and evaluate their significance are presented in **Figures 1**–**3**, and a series of photographic plates illustrating the variety of geometric, stratigraphic arrays, and lithology and mineralogy of volcanoes and volcanic geology are presented in **Figures 4**–**8**.

### **Figure 3.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

lapilli, a wide range of vesicle-lining or vesicle-filling minerals, crystal types and forms (*e.g.*, zeolites, calcite, quartz, chalcedony, epidote), mineral-filled fractures, small-scale fumarolic fissures or vents (empty, or filled with crystals, filled with massive lava, or filled with vesicular lava), alteration of the

*Following Brocx & Semeniuk [17], the four levels of significance recognised in this Chapter (modified from Brocx & Semeniuk [17, 18] and tailored for volcanoes): International, National, State-wide to Regional, and* 

*Local. Examples of many volcanoes and their deposits are included in this diagram.*

**332**

**Figure 2.**

*The Geoheritage Tool-kit used to systematically identify and assess sites of geoheritage significance (modified from Brocx & Semeniuk [17] and tailored for volcanoes).*

### **Figure 4.**

*The variety of geometric and stratigraphic arrays of volcanoes,* viz*., cinder cones, composite (stratovolcanoes), lava cones, and shield volcanoes. This diagram emphasises the gradation from tephra-dominated to lavadominated eruptions and the corresponding changes in stratigraphy and form of the volcanoes. Fissure vents, and sheet flows are not included.*

### **Figure 5.**

*Illustration of a selection of volcanic features at Jeju Island that are of geoheritage significance (photographs also are annotated). A. Bombs and dropstone structures in finer-grained tephra. B. Surge structures of megaripples and ripples in tephra. C & D. Polygonal (hexagonal) columnar jointing in basalt.*
