Volcanic Settings and Hotspots Lecture

Summary

This lab video explores volcanic activity and hotspot volcanism, focusing on how plate tectonics influence volcano formation. It covers four main volcanic settings: continental rift volcanism, subduction zones, volcanic island arcs, and hotspots. A key case study is the Hawaiian-Emperor seamount chain, which demonstrates plate motion. The video also explains the formation of calderas, using examples like Mount St. Helens and Krakatoa to illustrate how catastrophic eruptions impact elevation changes. By studying caldera chains like Yellowstone, we can measure plate motion over time, providing insights into the Earth's dynamic processes.

Takeaways

• 😀 Volcanoes form due to tectonic plate movements and are linked to plate tectonics, with different settings including continental rifting, subduction zones, and hotspots.
• 🌍 Continental rifting occurs when plates stretch and separate, allowing magma to rise and form volcanoes, like in the East African Rift Valley.
• 🌋 Subduction zones create volcanoes when one tectonic plate is forced beneath another, causing melting in the mantle and leading to the formation of continental volcanic arcs (e.g., Andes Mountains).
• 🌊 When oceanic plates subduct under other oceanic plates, volcanic island arcs are formed, such as the Aleutian Islands or the Philippines.
• 🔥 Hotspot volcanism occurs when a stationary mantle plume creates volcanoes as a plate moves across it, resulting in chains of volcanoes like the Hawaiian Islands.
• 📏 Hotspot volcanism can be used to determine plate motion by examining the age and location of volcanoes formed over a stationary hotspot.
• 🏞 Yellowstone and the Hawaiian Emperor Seamount Chain are key examples of hotspot chains that help track plate movement over time.
• 🧮 To calculate plate motion, we can measure the distance between volcanoes in a hotspot chain and use their ages to determine the rate of plate movement.
• 📉 Plate motion has slowed down over time; for example, the North American plate's average speed decreased from 5.2 cm/year to 3.8 cm/year between 17.3 and 12.5 million years ago.
• 🌋 A caldera is the collapsed magma chamber of a volcano, formed after a catastrophic eruption. The extent of elevation loss during a caldera formation indicates the size of the magma chamber and eruption severity.
• ⚖️ The percent change in elevation after a volcanic eruption, such as with Krakatoa, helps assess the scale of the eruption. Krakatoa's eruption caused a 26% loss in elevation, indicating a significant event.

Q & A

What are the three main goals of the lab as described in the transcript?

The three main goals of the lab are: 1) To understand how and why volcanoes form, the different volcanic settings under which they form, and their link to plate tectonics. 2) To understand the concept of hotspot volcanism and how it can be used as a tool to determine plate motion over time, with a case study of the Hawaiian Emperor Seamount chain. 3) To learn how calderas form, the controls determining the amount of elevation lost during an eruption, and why some volcanoes are more explosive than others.

What is the role of the Earth's plate movements in volcanic activity?

The movement of Earth's tectonic plates controls volcanic activity. Different types of volcanic settings are formed as a result of plate interactions, such as continental rifting, subduction, and hotspot volcanism. The movement of plates allows magma to rise to the surface, creating volcanoes.

What happens during continental rifting as seen in volcanic activity?

During continental rifting, the Earth's plates are stretched, creating rift valleys or cracks in the crust. These allow magma from the mantle to rise up and form volcanoes. The process occurs when the separation of plates depressurizes the mantle, allowing the hot mantle rock to melt and rise to the surface.

How does subduction lead to volcanic activity?

In subduction zones, one tectonic plate is forced beneath another. This causes melting in the mantle, and magma rises to the surface, forming volcanoes. When oceanic crust subducts under continental crust, a continental volcanic arc forms, while subduction of oceanic crust under other oceanic crust forms a volcanic island arc.

What is a hotspot, and how does it relate to volcanic activity?

A hotspot is a localized area where magma from deep within the Earth's mantle rises, forming volcanoes. Hotspot volcanism is different from tectonic-driven volcanic activity because the mantle plume responsible for the hotspot remains stationary while the tectonic plates move across it. This creates a series of volcanoes that are lined up as the plate moves.

How do hotspot volcanoes, such as those in Hawaii, form?

Hotspot volcanoes, like those in Hawaii, form as the tectonic plate moves over a stationary mantle plume. As the plate moves, the hotspot creates volcanoes in a linear chain. Each volcano forms over the hotspot and is then carried away as the plate continues to move, creating a chain of volcanoes.

What is the significance of the Hawaiian Emperor Seamount chain in studying plate motion?

The Hawaiian Emperor Seamount chain provides a case study for understanding plate motion over time. The alignment and ages of the volcanic islands in this chain allow scientists to track the movement of the Pacific plate across a stationary hotspot, providing insights into the rate and direction of plate movement.

What is a caldera, and how is it formed?

A caldera is a large, collapsed magma chamber created by a catastrophic volcanic eruption. When a volcano erupts violently, the ground above the magma chamber can collapse, forming a caldera. The size and elevation change resulting from the eruption are indicators of the magma chamber's size and the eruption's magnitude.

How do the eruption events of Mount St. Helens and Krakatoa differ in terms of their caldera formations?

Mount St. Helens and Krakatoa experienced violent eruptions that resulted in significant elevation changes and the formation of calderas. The difference between them lies in their eruption magnitudes and the degree of elevation loss. For example, Krakatoa's eruption caused a 26% reduction in elevation, a significant change that indicates a highly catastrophic eruption.

How is the rate of plate motion calculated using volcanic features like the Yellowstone caldera?

The rate of plate motion is calculated by measuring the distance between two volcanic features (e.g., calderas) and dividing it by the time elapsed between their formation. For instance, by measuring the distance between the McDermott caldera and the Yellowstone caldera, and knowing their respective ages, scientists can calculate the plate's average motion in centimeters per year.