Question

The following image shows the Buddhist monastery Taung Kalat, located in central Myanmar (Burma). The monastery sits high on a sheersided rock made mainly of magmas that solidified in the conduit of an ancient volcano. The volcano has since been worn away. a. Based on this information, what volcanic structure do you think is show in the photo? b. Would this volcanic structure most likely have been associated with a composite volcano or a cinder cone? Explain how you arrived at your answer.

Short answer

a. Volcanic plug; b. Associated with a composite volcano. Composite volcanoes more often form plugs due to their complex structure.

Step-by-step solution

Identify the Volcanic Structure

The information provided indicates that the monastery is situated on a solidified magma conduit of an ancient volcano. Such structures are typically described as a 'volcanic plug.' A volcanic plug is created when magma solidifies within a vent of a volcano, which can become exposed after the surrounding material has eroded away.

Determine Associated Volcano Type

Volcanic plugs can be associated with both composite volcanoes and cinder cones. However, they are more commonly related to composite volcanoes. Composite volcanoes (stratovolcanoes) tend to have more complex structures and eruptions that result in the solidification of magma plugs within the volcanic conduits.

Explain the Reasoning

Composite volcanoes are characterized by layers of lava, tephra, and volcanic ash, and they often have steep profiles. These characteristics can lead to the presence of solidified magma within the conduit, forming a volcanic plug as erosion takes place. Cinder cones are generally smaller, less steep, and less complex, making them less likely to feature prominent volcanic plugs.

Key concepts

Composite Volcano

Composite volcanoes, also known as stratovolcanoes, are large, symmetrical volcanoes composed of multiple layers of hardened lava, tephra, pumice, and volcanic ash. These layers build up over many eruptions, creating a stratified appearance, hence the name "composite." Composite volcanoes can be found in volcanic arcs around the world.

These volcanoes are well-known for their explosive eruptions, which are caused by thick, viscous lava that traps gases within the magma chamber. When the pressure becomes too great, it results in a powerful explosion, ejecting volcanic materials high into the atmosphere.

• The eruptions can be extremely hazardous due to pyroclastic flows, lahars, and ash falls.
• Because of the explosive nature, composite volcanoes often develop a central plug of solidified magma, also known as a volcanic plug.
• These plugs can become exposed over time through erosion, which effectively "peels away" the other materials.

Cinder Cone

Cinder cones are the simplest type of volcano. They are relatively small, steep-sided, and are built from particles and blobs of congealed lava ejected from a single vent.

Unlike composite volcanoes, cinder cones have less complex structures as they primarily consist of volcanic fragments known as cinders. These fragments cool rapidly and fall around the vent, accumulating to form a circular or oval cone.

• Cinder cones typically range from a few tens to a few hundreds of meters in height.
• The eruptions are often short-lived, but they can occur with little warning, spraying volcanic materials over a wide area.
• The lava from cinder cones is often basaltic in composition, resulting in less explosive eruptions compared to composite volcanoes.

Cinder cones usually lack the central plugs seen in composite volcanoes, as their eruptions do not typically create enough pressure to solidify magma within the conduit.

Volcanic Conduit

A volcanic conduit is a channel or pipeline through which magma travels from deep within the Earth's crust to the surface. This conduit connects the magma chamber to the volcanic vent.

The characteristics of the conduit can influence the nature of volcanic eruptions. For example, wider conduits can allow magma to rise more smoothly to the surface, resulting in gentle effusions of lava, while narrow conduits might build up pressure.

• The material that comes through a conduit becomes part of the volcanic vent and other surface formations like lava flows and tephra layers.
• As magma solidifies in the conduit, it can create a volcanic plug, particularly in cases where eruptions are explosive.
• Over time, the surrounding materials around a conduit may erode away, leaving the durable plug exposed as a significant geological feature.

Understanding the role of conduits in volcanic activity is important for predicting volcanic behavior and associated risks.

Volcano Erosion

Volcano erosion is the process by which volcanic structures are gradually worn down over time by natural forces such as wind, water, and ice. Erosion can significantly alter the appearance of a volcano, often revealing structures that were previously hidden.

Many volcanic features, like volcanic plugs, become prominent due to erosion. As softer materials like ash and loose tephra erode away, harder structures like solidified magma conduits remain intact.

• Volcanic plugs can protrude above the surface as the softer materials around them erode.
• This process takes place over millions of years, significantly changing the landscape.
• Erosion not only shapes landforms but also plays a role in exposing minerals and potentially valuable geological features.

By understanding erosion's impact on volcanic landscapes, geologists can learn about the history of volcanoes and predict future geological developments.