**6. Evidence of fissure-controlled volcanism**

ACVF preserves a range of fissure-controlled vents (**Figure 2**). Those vents are always aligned NE-SW with the regional tectonic trend (**Figure 6**). Along with those fissures, several small craters with exposed fissures can be observed, for example Tianchi/Heaven Lake (**Figures 6** and **7**) and Dichi Lake (**Figure 8**). These two vent systems are not only the scenic spots of ACVF, but also, they preserve the typical topography and landforms of fissure-fed volcanoes.

Fissure eruption are common in monogenetic volcanic fields [29]. In ACVF, at least five distinct fissures can be identified from satellite images. They appear as linear ridge crests associated with closely spaced crater rows (**Figure 2**). In general ACVF eruptions occur along fissures formed by regional faulting systems [1];

### **Figure 6.**

*Within Tianchi Lake, a shallow and elongated lake sitting well above the surrounding background topography suggesting the lake itself is a crater lake in a constructional volcanic landform such as a scoria cone. In both side (E and W) the elongated water-filled crater continuing into an elongated zone of depression surrounded by a spatter rampart (brown arrows). The overall orientation of the fissures is the same as the main structural setting of the ACVF (green arrow).*

**231**

**Figure 8.**

**Figure 7.**

*elevation as the lake floor itself (D).*

*Basic Volcanic Elements of the Arxan-Chaihe Volcanic Field, Inner Mongolia, NE China*

however, the volcanoes have yet to be documented in detail. An elongated vent structure is apparent on a satellite view of Tianchi/Heaven Lake (**Figure 6**). The central part of the lake is bumped out through the surrounding topography, which indicates the presence of steep-sided and agglutinated scoria/cinder cone as the main volcano architecture in that area (**Figure 6**). A series of the lava flows with large amounts of scattered spatter deposits can be seen on the western side of the lake (**Figure 6**). The shape of the lake suggests an outpouring may have occurred on the southeast section

*The GoogleEarth satellite image of the vicinity of Dichi Lake showing a chain of craters (brown dots) preserved* 

*oriented to the main structural zones of ACVF (green arrow).*

*The field observations of Tianchi Lake (A) area showing spatter ramparts, clastogenic lava flows in the eastern (B) and western (C) regions of the Tianchi Lake. Platy lava flows also crop out more or less in the same* 

*DOI: http://dx.doi.org/10.5772/intechopen.94134*

*Basic Volcanic Elements of the Arxan-Chaihe Volcanic Field, Inner Mongolia, NE China DOI: http://dx.doi.org/10.5772/intechopen.94134*

### **Figure 7.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

beds imply fallout origin.

**6. Evidence of fissure-controlled volcanism**

typical topography and landforms of fissure-fed volcanoes.

Bombs and accidental lithics in the eruptive products from Tongxin Volcano are commonly cored/loaded and/or granitoid lithics are fused or partially melted (**Figure 5B** and **C**). Cauliflower-shaped bombs with xenoliths are strong evidence for country-rock entrapment prior to the explosive disruption of the clasts during an eruption. Among the shell of the juvenile materials, large amounts of lithic debris are intercalated within. All these lithics are irregular-shaped, and, the juvenile materials are pasted onto the surface, chilled and form into the cauliflowershaped bombs or juvenile pyroclasts. The general shape of those juvenile pyroclasts is sub-angular to angular. They probably came into contact with external water and became chilled, fragmented in brittle fashion to form angular, low vesicular pyroclasts. Pyroclastic successions, which are rich in accidental lithics and contain large volumes of chilled, angular juvenile pyroclasts commonly form unsorted, and graded beds intercalated with fine tuff that also contains accretionary lapilli (**Figure 5D**). These textural features and outcrop scale sedimentological characteristics are common among phreatomagmatic pyroclastic successions. Commonly, the fine-sized grains indicate the explosive phreatomagmatic fragmentation was accompanied by blasts; on the contrary, the coarse-grained and moderately sorted

ACVF preserves a range of fissure-controlled vents (**Figure 2**). Those vents are always aligned NE-SW with the regional tectonic trend (**Figure 6**). Along with those fissures, several small craters with exposed fissures can be observed, for example Tianchi/Heaven Lake (**Figures 6** and **7**) and Dichi Lake (**Figure 8**). These two vent systems are not only the scenic spots of ACVF, but also, they preserve the

Fissure eruption are common in monogenetic volcanic fields [29]. In ACVF, at least five distinct fissures can be identified from satellite images. They appear as linear ridge crests associated with closely spaced crater rows (**Figure 2**). In general ACVF eruptions occur along fissures formed by regional faulting systems [1];

*Within Tianchi Lake, a shallow and elongated lake sitting well above the surrounding background topography suggesting the lake itself is a crater lake in a constructional volcanic landform such as a scoria cone. In both side (E and W) the elongated water-filled crater continuing into an elongated zone of depression surrounded by a spatter rampart (brown arrows). The overall orientation of the fissures is the same as the main structural* 

**230**

**Figure 6.**

*setting of the ACVF (green arrow).*

*The field observations of Tianchi Lake (A) area showing spatter ramparts, clastogenic lava flows in the eastern (B) and western (C) regions of the Tianchi Lake. Platy lava flows also crop out more or less in the same elevation as the lake floor itself (D).*

### **Figure 8.**

*The GoogleEarth satellite image of the vicinity of Dichi Lake showing a chain of craters (brown dots) preserved oriented to the main structural zones of ACVF (green arrow).*

however, the volcanoes have yet to be documented in detail. An elongated vent structure is apparent on a satellite view of Tianchi/Heaven Lake (**Figure 6**). The central part of the lake is bumped out through the surrounding topography, which indicates the presence of steep-sided and agglutinated scoria/cinder cone as the main volcano architecture in that area (**Figure 6**). A series of the lava flows with large amounts of scattered spatter deposits can be seen on the western side of the lake (**Figure 6**). The shape of the lake suggests an outpouring may have occurred on the southeast section of the present-day water-filled, lacustrine basin (**Figure 7A**). Two other locations marking fissure structures on both sides of the lake, are shown by the large green arrow on **Figure 6**. The orientation of the fissures implies Tianchi Lake too follows the orientation of the regional structures (NE-SW). The brown dots on **Figure 6** indicator two rows of spatter and lava ramparts surrounding the margins of an eruptive fissure. This morphological setting and the presence of proximal spatter deposits, and clastogenic lava flows are interpreted to be the result of fissure eruptions that formed the Tianchi Lake Volcano. Also, the angle of repose of the main cone of Tianchi Lake Volcano is nearly 37–41 degrees suggesting a relatively young age of the volcano as Tianchi Lake Volcano is a scoria cone similar to other scoria cones in the world, i.e. the one in AVF (Auckland Volcanic Field) [30]. The total surface area of Tianchi Lake is approximately 0.1 km2 , with about 1.2 km in its perimeter. The wellestablished forests and vegetation around the lake field observations and sampling difficult (**Figure 7A**). However, on the outer rim of the lake and the surrounding areas, volcanic materials are well-exposed and easily sampled.

Preliminary observations on the Tianchi Lake Volcano so far have been interpreted as it is a complex, elongated scoria cone. No phreatomagmatic deposits have been identified yet in the area suggesting that the volcano, despite it hosting a shallow lake, formed purely by magmatic explosive and effusive processes. During the dry season (August to October, annually), the height of the water level of the crater lake drops a few metres (**Figure 7A**). Along the eastern and western side of the preserved scoria cone, the fissure is marked by a 10 meters high wall of lava consisting of flows and spatter ramparts. Evidence of agglutinated interbeds within lava flows as well as some of clastogenic origin flows attests to fissure lava fountaining and shifting of active vent locations occurring. The surface structures of the fissure are similar to the lava flow, but are considerably harder, thereby preserving the original volcano architecture well. Occasionally, some lithic xenoliths (granite) can be observed within the spatter and lava flows. The rarity of vesicles in the lava flows and the agglutinated texture suggest the lava was degassed during the eruption, indicating that some sort of lava pool must have occupied the main axis of vents. On the western side of the main cone (**Figure 7C**), an approximately 50 m high wall of weakly stratified agglomerate and interbedded clastogenic lava flows formed due to explosive magmatic eruptions from a sustained lava fountaining stage forming a wall-like topography. in the middle part of the "wall", a small gap between them might be the fissure structures aligning with the orientation. Field observations could only be taken from one side of the branch of the Halaha River. On the other side the bedded and agglutinated nature of the rocks are clearly visible suggesting the proximal location of the region. The horizontally stratified structures of the "wall" might indicate various stages of the cone building as well as the longevity of the eruptive phase. The thickness of the lava flows in the western side of the Tianchi/Heaven Lake is about 4–6 m (**Figure 7D**). The lava displays textures consistent with fluid transportation; there are also a moderate amount of bubbles. Within the bulk rock, some mafic minerals, including olivines and pyroxenes, can be seen. The top of these lava flow structures is eroded by the vegetation, but in some places the typical structures of aa type are still preserved.

Along with Tianchi/Heaven Lake, Dichi Lake is another small vent sitting on a fissure estimated to be about 3 km long. This lake might be the smallest one in ACVF (**Figure 8**). The green arrow on **Figure 8** marks the regional trend of the fissure orientation, which is also NE–SW, same orientation as Tianchi Lake. In comparison to Tianchi Lake, this fissure system is narrower but longer. The surrounding topography is flat without the tiny bumps due to local tumuli (**Figure 8**). Observations from the proximal areas of the Dichi Lake confirms the presence of pyroclastic breccias composed of dm-to-m sized angular blocks of lava commonly

**233**

**Figure 9.**

*(explosion crater) in the fissure edge.*

*Basic Volcanic Elements of the Arxan-Chaihe Volcanic Field, Inner Mongolia, NE China*

forming well-defined zones several metres across. This deposit is estimated to be a few metres thick and sitting on a lava platform exposed in the crater wall of the Dichi Lake. There is no sign of deposits that may indicate PDC-generating eruptions or accumulation of typical base surge deposits. On the basis of this observation, Dichi Lake is likely a product of a short-lived, single explosive blast triggered by magma-water interaction along a fissure when the fissure hit the lowermost point of

In the densely vegetated area of the Dichi Lake a volcanic cone chain (**Figure 9A**) with small preserved craters is still recognizable (**Figure 9B**). On the top of the small volcanic cones along the fissure, large blocks of scoria can be found hosting dm-sized spindle-shaped bombs (**Figure 9D**). The reddish color of most of the recovered

*The field observations of Dichi Lake show small (tens of metres across) crater chains (a) with shallow but recognizable craters (B). In the crater wall of DIchi Lake lava flows exposed that are covered by pyroclastic breccia deposits (C). In the flank of the crater chains, fluidly shaped lava bombs suggest proximal portions of those areas (D). Dichi Lake best to interpret as a result of a single, short-lived phreatomagmatic blast* 

*DOI: http://dx.doi.org/10.5772/intechopen.94134*

bombs indicates high-temperature emplacement.

the region (**Figure 8**).

*Basic Volcanic Elements of the Arxan-Chaihe Volcanic Field, Inner Mongolia, NE China DOI: http://dx.doi.org/10.5772/intechopen.94134*

forming well-defined zones several metres across. This deposit is estimated to be a few metres thick and sitting on a lava platform exposed in the crater wall of the Dichi Lake. There is no sign of deposits that may indicate PDC-generating eruptions or accumulation of typical base surge deposits. On the basis of this observation, Dichi Lake is likely a product of a short-lived, single explosive blast triggered by magma-water interaction along a fissure when the fissure hit the lowermost point of the region (**Figure 8**).

In the densely vegetated area of the Dichi Lake a volcanic cone chain (**Figure 9A**) with small preserved craters is still recognizable (**Figure 9B**). On the top of the small volcanic cones along the fissure, large blocks of scoria can be found hosting dm-sized spindle-shaped bombs (**Figure 9D**). The reddish color of most of the recovered bombs indicates high-temperature emplacement.

### **Figure 9.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

areas, volcanic materials are well-exposed and easily sampled.

some places the typical structures of aa type are still preserved.

Along with Tianchi/Heaven Lake, Dichi Lake is another small vent sitting on a fissure estimated to be about 3 km long. This lake might be the smallest one in ACVF (**Figure 8**). The green arrow on **Figure 8** marks the regional trend of the fissure orientation, which is also NE–SW, same orientation as Tianchi Lake. In comparison to Tianchi Lake, this fissure system is narrower but longer. The surrounding topography is flat without the tiny bumps due to local tumuli (**Figure 8**). Observations from the proximal areas of the Dichi Lake confirms the presence of pyroclastic breccias composed of dm-to-m sized angular blocks of lava commonly

Tianchi Lake is approximately 0.1 km2

of the present-day water-filled, lacustrine basin (**Figure 7A**). Two other locations marking fissure structures on both sides of the lake, are shown by the large green arrow on **Figure 6**. The orientation of the fissures implies Tianchi Lake too follows the orientation of the regional structures (NE-SW). The brown dots on **Figure 6** indicator two rows of spatter and lava ramparts surrounding the margins of an eruptive fissure. This morphological setting and the presence of proximal spatter deposits, and clastogenic lava flows are interpreted to be the result of fissure eruptions that formed the Tianchi Lake Volcano. Also, the angle of repose of the main cone of Tianchi Lake Volcano is nearly 37–41 degrees suggesting a relatively young age of the volcano as Tianchi Lake Volcano is a scoria cone similar to other scoria cones in the world, i.e. the one in AVF (Auckland Volcanic Field) [30]. The total surface area of

established forests and vegetation around the lake field observations and sampling difficult (**Figure 7A**). However, on the outer rim of the lake and the surrounding

Preliminary observations on the Tianchi Lake Volcano so far have been interpreted as it is a complex, elongated scoria cone. No phreatomagmatic deposits have been identified yet in the area suggesting that the volcano, despite it hosting a shallow lake, formed purely by magmatic explosive and effusive processes. During the dry season (August to October, annually), the height of the water level of the crater lake drops a few metres (**Figure 7A**). Along the eastern and western side of the preserved scoria cone, the fissure is marked by a 10 meters high wall of lava consisting of flows and spatter ramparts. Evidence of agglutinated interbeds within lava flows as well as some of clastogenic origin flows attests to fissure lava fountaining and shifting of active vent locations occurring. The surface structures of the fissure are similar to the lava flow, but are considerably harder, thereby preserving the original volcano architecture well. Occasionally, some lithic xenoliths (granite) can be observed within the spatter and lava flows. The rarity of vesicles in the lava flows and the agglutinated texture suggest the lava was degassed during the eruption, indicating that some sort of lava pool must have occupied the main axis of vents. On the western side of the main cone (**Figure 7C**), an approximately 50 m high wall of weakly stratified agglomerate and interbedded clastogenic lava flows formed due to explosive magmatic eruptions from a sustained lava fountaining stage forming a wall-like topography. in the middle part of the "wall", a small gap between them might be the fissure structures aligning with the orientation. Field observations could only be taken from one side of the branch of the Halaha River. On the other side the bedded and agglutinated nature of the rocks are clearly visible suggesting the proximal location of the region. The horizontally stratified structures of the "wall" might indicate various stages of the cone building as well as the longevity of the eruptive phase. The thickness of the lava flows in the western side of the Tianchi/Heaven Lake is about 4–6 m (**Figure 7D**). The lava displays textures consistent with fluid transportation; there are also a moderate amount of bubbles. Within the bulk rock, some mafic minerals, including olivines and pyroxenes, can be seen. The top of these lava flow structures is eroded by the vegetation, but in

, with about 1.2 km in its perimeter. The well-

**232**

*The field observations of Dichi Lake show small (tens of metres across) crater chains (a) with shallow but recognizable craters (B). In the crater wall of DIchi Lake lava flows exposed that are covered by pyroclastic breccia deposits (C). In the flank of the crater chains, fluidly shaped lava bombs suggest proximal portions of those areas (D). Dichi Lake best to interpret as a result of a single, short-lived phreatomagmatic blast (explosion crater) in the fissure edge.*
