Pyroclastic
Deposits - John Seach
Three types
of pyroclastic deposits
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Fall deposits
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Drape the landscape. Well sorted.
Deposited cool. Vertical trajectory. |
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Surge deposits
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Do not evenly drape the landscape,
but pinch and swell. Vary from poor to well sorted. Transient high temperatures
such as burn victims or carbonised vegetation. Horizontal trajectory. |
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Flow deposits
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Confined to valleys. Poorly sorted.
High temperation deposition indicated
by carbonised vegetation, thermal oxidation colours, and eruption welding.
Horizontal trajectory. |
A pyroclastic
surge is a turbulent cloud of gas and rock fragments that flows across
the ground.
Surges are
not constrained by topography but can move over obstacles such as ridges
and hills.
There are 4 factors operating during
deposition
-
Trajectories of particles from vertical
to horizontal
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Concentration of particles in the deposited
material.
-
Fluctuation in deposition rate. Determines
degree of sorting.
-
Degree of cohesion. More cohesive means
longer lasting deposits.
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Pyroclastic Deposits
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Copyright John Seach
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