Material is ejected from volcanoes due to gas pressure. At depth the pressure is great enough to keep the gas dissolved in the magma. As the magma enters the throat of the volcano the bubbles form and begin to grow. The violent bursting of bubbles fragments the lava and sends it into the air. Lava, pyroclasts, and gas comes out of volcanoes. Pyroclasts are classified by size. Ash is the smallest pyroclasts. Blocks and bombs are the largest. Cinder and pumice are also types of pyroclasts. Water vapor, carbon dioxide, and sulfur dioxide are the most common gases. Less common gasas are carbon monoxide, sulfur, chlorine, flourine, hydrochloric acid.
Pyrclasts are the probably the best known volcanic ejecta, next to lava.
Volcanologists go out into the field to figure out the distribution of erupted
pyroclastic material. They will go to numerous sites around the volcano and
measure (in general) 3 things:
1) the total thickness of the pyroclastic deposit at each location
2) the average size of the 10 largest pumices at each location
3) the average of the 10 largest lithic clasts at each location (a lithic
is a pre-existing rock that is included in the explosive eruption).
They then draw contours around the data that they have collected. In some
cases, if the geologists are studying a very old eruption, they may not even
know where the vent was. The contours of the thickness and size measurements
should close around the vent so that its location can be determined.
Look at that stuff! Ash and lava explodes out because of tremendous pressure.
The finer particles in ash will be blown up into the troposphere or stratosphere
and be swept away by winds. They cause ash clouds and if they are not blown
high enough into the atmosphere, will be washed down by rain in a matter
of days. Ash that drifts up to the stratosphere may cause significant changes
in the temperatures of nearby, or even global locations.
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