The structural instability that turns massive volcanoes into deadly landslides
In short: When a volcano loses its structural integrity, it doesn't just erupt; it can physically disintegrate. This phenomenon, known as sector collapse, involves the failure of at least 1 cubic kilometer of a volcano, potentially triggering lateral blasts, massive mudflows, and even tsunamis.
Sector collapse, or edifice failure, occurs when a significant portion of a volcano's structure gives way. While these events are often sudden and difficult to predict, they are driven by a complex interplay of internal and external forces. Internally, rising magma, magmatic intrusions like dikes, and volcanic eruptions can destabilize magma chambers or fracture rock. Externally, earthquakes, intense rainfall, and even sea level changes can weaken a volcano's stability. In some cases, the slope simply reaches a critical angle of repose, leading to gravity-induced collapse.
A particularly insidious driver is hydrothermal alteration. In stratovolcanoes like Mount Rainier, andesitic rock is exposed to hot liquids or gases for long periods. This process causes physical and chemical changes, transforming the rock into a much weaker material containing clay. At Mount Rainier, this alteration is widespread, particularly in an East-West Zone. This weakened structure is highly susceptible to failure, especially when combined with steep slopes and high relief.
The consequences of such failures are often catastrophic. The 1980 collapse of Mount St. Helens in the Cascades triggered an immediate lateral blast. At Mount Rainier, at least three major collapses have occurred in the past; the largest removed the northeast slope and summit, initiating the Osceola Mudflow, the mountain's largest lahar. Beyond landslides and lahars, these events can trigger phreatic eruptions due to reduced pressure in the magma chamber. Historically, sector collapses and their resulting landslides have caused over 3,500 fatalities since 1600, including a tsunami from the Oshima-Oshima collapse that killed 1,500 people.
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Sources
- Summary by Intellect · source: Sector Collapse | Department of Geography & Environmental Studies
- Also: Sector collapse
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