**8. Evidence of lava-ponding in craters and topography lows**

Lava ponding in ACVF is another feature characteristic of the volcanism in the region. The topography of the lava flows indicates an overwhelming dominance of various types of aa and rubbly pahoehoe lava flow morpho-types for the ACVF.

In ACVF, not only are small vents formed, but also, large craters formed that acted as traps for lava flows. In addition, lava commonly ponded in local basins or valley networks. A large crater (about 1.1 km across) from where one of the youngest and most extensive lava flows initiated to forms a significant volcanic landform with a typical volcanic morphology (**Figure 11**). The local name for this location as Dahei Gou, where it means "the big melanocratic valley". Actually, there are two territories with the same name, but in considerations to the descriptions of volcanism of ACVF, the name "Dahei Gou" can only be a marker to define this unique location of ponded lava in a large crater. Dahei Gou Crater is located about 4.9 km northeastern of the three young volcanic cones of Yanshan (**Figure 11**). The satellite image (**Figures 2** and **11**) indicates that these two groups of vents (cones) have the same orientation as the Tianchi and Dichi fissures. Thus, it is believed there are at least two major regional structures controlling the vent distributions of ACVF.

The Dahei Gou crater is heavily vegetated, and only small tracks lead to the remote interior of a complex crater system. From the entrance of the valley,

### **Figure 11.**

*The satellite view of Dahei Gou (big Black Valley), also this photo depicts the relationship with Yanshan-triple vent. The dashed line indicates the extrapolation of the major fissure trend. The blue curve marks the caldera rim of Dahei Gou.*

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

Spatter deposits are the typical dry eruption phase during the building of volcanic cones. In ACVF, spatter deposits are shown on the vents, which are scoria cones or fissure-related vents, such as Dichi Lake. However, one location preserves intact spatter deposits in the basal section of Tongxin Volcano (**Figure 10A**). The rest of the vents in ACVF only preserve scoria deposits from non-welded (black) to welded

At Tongxin Volcano, the basal pyroclastic deposits along the western rim of the phreatomagmatic volcano preserve an about 2 m thick undulating, laterally discontinuous spatter unit (**Figure 10A**). On the top of the spatter unit, 30–50 cm of unsorted and laterally continuous PDC deposits were found suggesting dramatic eruption style change from a lava fountain stage to a phreatomagmatic blast eruption prior to the eruption becoming more sustained phreatomagmatic in style. Here the spatter deposits are in contact with the country-rock. Based on the contact relationships, Tongxin Volcano might have experienced an initial dry-eruptive phase followed by explosive phreatomagmatism. The distribution of the spatter deposits on Tongxin Volcano are elongated and expanded about 30 m long. On both ends of the spatter deposit, the thickness is thinner than the thickness on the middle part, and the shape is lens-like. Large accidental lithic bombs and blocks are commonly

*The spatters deposits on the northwestern side of Tongxin Lake (A). The blue letter "G" means "granite" for country-rocks. Spatter deposits lay on the bedrocks (B), and granitoid lithics commonly captured within the* 

**7. Evidence of spatter-dominated volcanism**

(red) varieties.

**234**

**Figure 10.**

*spatter deposit (C).*

where the main lava flows spread along the Halaha River valley to the crater is about 4 km (**Figure 11**). The valley from the crater is filled with about 1 km wide lava flow along 4 km length, exposing typical flow margin features such as small to mediumsized tumuli and pressure ridges (**Figure 12A** and **B**).

Within the crater, a breakout zone can be identified along which the lava flow outpoured. In that area, rafted spatter sections and large slabs of lava in a randomly packed chaotic nature is evident. Inside the crater, individual tumuli, ramped up lava rubble and large piles of aa blocks form a rugged topography. Along the crater margin, lava flows preserve several meter-long cracks parallel with the crater margin (**Figure 12D**). These zones are interpreted as fractures along the inflated and ponded intra-crater where ponded lava collapsed upon the partial emptying of the large crater. The major body of the intra-crater lava flow is shown in **Figure 12C**. Along the crater margin, on the inner crater wall, drain back features can be seen that are partially collapsed back to the crater suggesting a dramatic outpouring event tapped the lava toward the valley. Dahe Gou is composed of at least three major nested crater systems, indicating vent migration, crater infill and sudden lava release forming a pit-like crater system. The total area of this crater is approximately 1 km<sup>2</sup> . The perimeter is about 4 km (**Figure 11**). Observations from the field indicate the presence of scoriaceous pyroclastic beds and agglomerate layers that formed due to explosive magmatic eruptions. On the eastern flank of the Dahe Gou, thick, black scoria ash drapes the landscape that has been partially down-cut by erosion (**Figure 11**). The textural similarities and the proximity of these ash plains to Yanshan deposits suggests that it might be part of the youngest eruptions of the Yanshan – Gaoshan volcanic system; however, this needs to be confirmed in future research.

### **Figure 12.**

*The major characteristics of Dahei Gou. Lava flows from the Dahei Gou shows pahoehoe surface textures in the lava fan regions with vesicles aligned following inflationary features (A), while deflationary features leaving behind collapsed lava tube roofs (B). The crater is filled with remaining parts of collapsed ponded lava zones, and along with the crater margins lava drawback features are prominent (C). Along the crater margins, margin-parallel cracks indicate collapse events (D).*

**237**

**Figure 13.**

*about 500 m above the valley floor (D).*

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

In the Arxan region, where lava flows are captured in the river valley, they form tumuli and lava tube networks that are partially collapsed, e.g. the fluvial areas of Halaha River. Such areas are prominent around the Wusulangzi Lake and Tianchi Lake (**Figure 13**). Eventually, in these areas, the lava flows are ponded around and form a range of significant landforms, some of them have already become the scenic

Along Halaha River large lava caves are partially open reaching a width of about 4 metres (**Figure 13A**). The lava flows formed successive layers with unambiguous and parallel boundaries. This suggests the flows ponded during several influx stages contemporaneously. The lava dripped from the ceiling (**Figure 13B**) but had no time on the ground consolidating while the processes were ongoing giving them a typical shape that is well preserved. Due to the roughness of the lava flow surface, the ponded lakes developed as the Halaha River became blocked (**Figure 13C**). The lake is no more than 6 m deep. Some of the ponded lakes have been misinterpreted as the sites of small cones; however, they are tumuli that formed along the flow margin. Cone and star shape tumuli displaying the cone shape forma group of dozens of tumuli in this region (**Figure 13D**). The cracks on the top of the tumuli indicate the upwelling and shape-forming processes were accompanied by tremendous volumes of steam. During the slow movement of lava flows, the gas and vaporized steam would occasionally gather and form large bubbles. Some of them were emitted through the surface of the flow. Thus, the inner parts of the tumuli are empty voids with a cone shape. In the Halaha River area, some tumuli are linear in shape (about 4 m in length and about 3 m in height) and align with each other.

*The ponded lava flow topography around fluvial areas of Halaha River exposes partially open lava tubes (A) that are draped by lava stalagmites (B). The blocked Halaha River forms a network of lakes and swamps (C). Tumuli are typically formed in the flat Halaha River valley where the cooling effect slowed down and eventually ponded the lava flows derived from the Dahei Goe volcano and Yanshan- Gaoshan volcanic system* 

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

Most are similar size and volume.

spots for the volcanological educational purposes.

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

In the Arxan region, where lava flows are captured in the river valley, they form tumuli and lava tube networks that are partially collapsed, e.g. the fluvial areas of Halaha River. Such areas are prominent around the Wusulangzi Lake and Tianchi Lake (**Figure 13**). Eventually, in these areas, the lava flows are ponded around and form a range of significant landforms, some of them have already become the scenic spots for the volcanological educational purposes.

Along Halaha River large lava caves are partially open reaching a width of about 4 metres (**Figure 13A**). The lava flows formed successive layers with unambiguous and parallel boundaries. This suggests the flows ponded during several influx stages contemporaneously. The lava dripped from the ceiling (**Figure 13B**) but had no time on the ground consolidating while the processes were ongoing giving them a typical shape that is well preserved. Due to the roughness of the lava flow surface, the ponded lakes developed as the Halaha River became blocked (**Figure 13C**). The lake is no more than 6 m deep. Some of the ponded lakes have been misinterpreted as the sites of small cones; however, they are tumuli that formed along the flow margin. Cone and star shape tumuli displaying the cone shape forma group of dozens of tumuli in this region (**Figure 13D**). The cracks on the top of the tumuli indicate the upwelling and shape-forming processes were accompanied by tremendous volumes of steam. During the slow movement of lava flows, the gas and vaporized steam would occasionally gather and form large bubbles. Some of them were emitted through the surface of the flow. Thus, the inner parts of the tumuli are empty voids with a cone shape. In the Halaha River area, some tumuli are linear in shape (about 4 m in length and about 3 m in height) and align with each other. Most are similar size and volume.

### **Figure 13.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

sized tumuli and pressure ridges (**Figure 12A** and **B**).

approximately 1 km<sup>2</sup>

confirmed in future research.

where the main lava flows spread along the Halaha River valley to the crater is about 4 km (**Figure 11**). The valley from the crater is filled with about 1 km wide lava flow along 4 km length, exposing typical flow margin features such as small to medium-

Within the crater, a breakout zone can be identified along which the lava flow outpoured. In that area, rafted spatter sections and large slabs of lava in a randomly packed chaotic nature is evident. Inside the crater, individual tumuli, ramped up lava rubble and large piles of aa blocks form a rugged topography. Along the crater margin, lava flows preserve several meter-long cracks parallel with the crater margin (**Figure 12D**). These zones are interpreted as fractures along the inflated and ponded intra-crater where ponded lava collapsed upon the partial emptying of the large crater. The major body of the intra-crater lava flow is shown in **Figure 12C**. Along the crater margin, on the inner crater wall, drain back features can be seen that are partially collapsed back to the crater suggesting a dramatic outpouring event tapped the lava toward the valley. Dahe Gou is composed of at least three major nested crater systems, indicating vent migration, crater infill and sudden lava release forming a pit-like crater system. The total area of this crater is

the field indicate the presence of scoriaceous pyroclastic beds and agglomerate layers that formed due to explosive magmatic eruptions. On the eastern flank of the Dahe Gou, thick, black scoria ash drapes the landscape that has been partially down-cut by erosion (**Figure 11**). The textural similarities and the proximity of these ash plains to Yanshan deposits suggests that it might be part of the youngest eruptions of the Yanshan – Gaoshan volcanic system; however, this needs to be

*The major characteristics of Dahei Gou. Lava flows from the Dahei Gou shows pahoehoe surface textures in the lava fan regions with vesicles aligned following inflationary features (A), while deflationary features leaving behind collapsed lava tube roofs (B). The crater is filled with remaining parts of collapsed ponded lava zones, and along with the crater margins lava drawback features are prominent (C). Along the crater margins,* 

. The perimeter is about 4 km (**Figure 11**). Observations from

**236**

**Figure 12.**

*margin-parallel cracks indicate collapse events (D).*

*The ponded lava flow topography around fluvial areas of Halaha River exposes partially open lava tubes (A) that are draped by lava stalagmites (B). The blocked Halaha River forms a network of lakes and swamps (C). Tumuli are typically formed in the flat Halaha River valley where the cooling effect slowed down and eventually ponded the lava flows derived from the Dahei Goe volcano and Yanshan- Gaoshan volcanic system about 500 m above the valley floor (D).*
