A sector collapse or lateral collapse is the structural failure and subsequent collapse of a minimum volume of of a volcano.
Causes
Internal
Sector collapse can result from internal volcanic processes. Volcanic eruption can damage originally stable
Magma chamber, causing a portion of the volcano to collapse.
While eruption is one cause, sector collapse can occur without any eruption.
Magma intrusions can also lead to sector collapse. Dikes fracture and deform rock, leaving the volcano weaker and more susceptible to collapse. Hydrothermal activity is another internal cause, likely due to reactions of
acid-
Sulfate weakening
volcanic rock. Gravity-induced collapse occurs when the volcanic slope approaches the critical angle of repose.
The slope angle is a major factor in collapse events.
External
Sector collapse sometimes occurs because of external processes.
Earthquake is a prominent cause of collapse events. Earthquakes can weaken the structural stability of volcanoes, leading to sudden collapse or contributing to a later collapse. Intense
weather and heavy
Rain can cause damaging erosion, increasing likelihood of collapse.
Glacial melting is another external cause of sector collapse, with the majority of glacial melt induced collapses occurring during the
Pleistocene. Glacial melting increases volcanic slope and decreases pore pressure, leading to sector collapse.
Sea level change has also been associated with sector collapse.
Predicting sector collapse
Because sector collapse events occur suddenly and over small time periods, they are difficult to predict.
More often, volcanoes are assessed for risk of sector collapse.
Collapse ultimately occurs due to structural instability,
which can be determined by volcanic slope angle, composition of the volcano, deformation, and other factors.
Consequences
Changes to volcanic systems
Some volcanoes experience no changes in volcanic behavior while others experience altered rates of eruption and magma composition.
Collapse is typically followed by phreatic eruption
due to a reduction in
magma chamber pressure after sector collapse. Damage caused by collapse can create a new and different volcanic plumbing system, which could impact eruption rates. Sector collapse often results in eruption of more
mafic magma. Large overlying surface mass and the denser nature of mafic magma often prevents its rise. Collapse relieves some of the overlying surface mass thus allowing for more mafic magma composition.
Human impacts
Sector collapses and landslides caused by them have directly resulted in more than 3,500 fatalities since 1600 and caused extensive property damage. A particularly deadly consequence of sector collapse is
tsunami. The Oshima-Oshima collapse led to a tsunami that killed 1,500 people. Sector collapse events can also displace thousands and cause
homelessness.
Identifying sector collapse
Prehistory sector collapses are stored in the
Geologic record in the form of debris avalanche deposits
and collapse scars. Debris avalanche deposits are found typically up to from the site of collapse,
but in the case of the Hawaiian islands away.
Studying avalanche deposits informs on the time scale of the collapse and the volcano from which it originated.
Collapse scars are also an indicator of sector collapse and are often described as "
amphitheatre" or "
horseshoe" shaped.
One such collapse scar is the Sciara del Fuoco formed on the
Stromboli due to a sector collapse.
Examples
Prehistoric
Historic
See also
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