Question

Which of the following forms when the top of a volcano collapses into a partially emptied magma chamber? A. fissure C. caldera B. crater D. Volcanic neck

Short answer

Caldera.

Step-by-step solution

Understand the Question

The question is asking about a geological feature that forms when the top of a volcano collapses. This collapse is specifically into a partially emptied magma chamber, which is crucial to finding the correct option.

Analyze the Options

We have four options: fissure, caldera, crater, and volcanic neck. A fissure is typically a long crack or opening in the Earth's crust. A crater is usually a bowl-shaped depression, often formed around a volcanic vent. A volcanic neck is the remnants of the solidified conduit of a volcano. A caldera is a large depression that forms after a magma chamber empties and collapses.

Identify the Correct Answer

From the description, we know that a caldera forms when a volcano's top collapses into a partially emptied magma chamber. This matches the scenario provided in the question. The other options do not fit this specific description.

Key concepts

Volcanic Collapse

When a volcano experiences a collapse, it is considered a major geological event. This happens after a significant amount of magma has been expelled from the magma chamber, leaving a void. The weight of the rocks above this void becomes unsustainable, causing the top of the volcano to give way. This creates a large depression known as a caldera. Such collapses are typically more severe than simple craters, as they involve a much larger portion of the volcano structure. Volcanic collapse typically occurs after a violent volcanic eruption. As magma exits, enormous pressure that once supported the rock above the chamber decreases. The collapse not only involves the central part of the volcano but may affect surrounding areas, altering the landscape dramatically.

Magma Chamber

The magma chamber is a crucial part of a volcano’s anatomy. It is a subterranean reservoir where magma accumulates beneath the Earth's surface. This chamber is linked to the surface by vents and conduits through which magma travels during an eruption.

• Composed of molten rock: A mix of liquids, crystals, and gas.
• Can be located several kilometers below the surface of the Earth.
• Feeds eruptions: Spews out magma during volcanic activity.

When a magma chamber empties, it can no longer support the weight of the crust above it, leading to volcanic collapse and the formation of a caldera. Understanding magma chambers is essential for predicting volcanic behavior and the potential for explosive eruptions.

Geological Features

Geological features are natural structures and formations that make up the landscape. Volcanoes are one of the most prominent geological features on Earth. These features result from various geological processes, including plate tectonics and erosion. Volcanoes themselves contribute to the creation of other unique geological features like lava flows, pyroclastic flows, and ash deposits. They are also responsible for more dramatic formations such as calderas and craters when collapse or eruption occurs. Geological features are not static; they change over time due to natural forces. Studying these features gives insight into the Earth's geological history and helps in forecasting natural disasters like volcanic eruptions.

Volcanic Structures

Volcanic structures encompass all the physical components associated with a volcano. They vary widely depending on the type of volcano and its eruptive history. Broadly, they can include cones, craters, lava domes, and calderas.

• Cones: Built by eruptions that pile up ash or lava flows.
• Craters: Bowl-shaped depressions that form from explosive activity.
• Domes: Thick and slow-moving lava piles up near the vent.
• Calderas: Large depressions formed from significant volcanic collapse.

Understanding these structures helps geologists predict future volcanic activity and assess potential hazards. Each structure formed leaves clues about past eruptions and the dynamics of the magma that fed them.