Why are most active volcanoes associated with plate tectonic boundaries?
Spreading of sinking plates interact at plate boundaries with other materials to produce magma
Viscosity of a magma is controlled by...
Temperature and silicon content of the magma
The shape of shield volcanoes is a function of...
Lava viscosity
Why do composite volcanoes consist of alternating lava and pyroclastic layers?
Composite cones are created by a mixture of explosive activity and lava flows
Mid-ocean ridge volcanism produces what type of volcanic rock?
Basalt
Composite cones typically are associated with what type of plate tectonic feature?
Subduction zone
What is the principle difference between craters and calderas?
Calderas are much larger depressions created by collapse of the upper portions of the volcano
Why were the citizens of Heimaey, Iceland, successful in stopping the lava flow that threatened their harbor?
They had a ready supply of water with which to to chill the lava
The number of fatalities from the Mt. Pinatubo eruption was relatively low because...
The eruption was predicted successfully, and the area was evacuated
What is one reason that ash fall is such a significant hazard?
The weight of the ash can cause structural damage to buildings
A Lahar is produced when...
Ash and other pyroclastic ejecta become saturated with water
Hundreds of residents near a dormant volcano at lake Nyos died when...
A dense cloud of volcanic gas was released
Seismic activity serves as a tool of volcanic forecasting because...
Moving magma causes earthquakes
Why is the geologic history of a volcano important in hazard prediction?
The geologic history reveals the frequency and style of eruptions
Why is topographic monitoring sometimes useful in forecasting a volcanic eruption?
A volcano sometimes swells as lava moves into the edifice
