volcanoes Flashcards
Most magma is generated in the…
lower crust/upper mantle region
The explosiveness of volcanoes depends on the…
viscosity and the amount of gas
dissolved and trapped in the magma
Magma viscosity is dependent on its…
silica content and temperature. The lower the
temperature the greater the viscosity. The higher the silica content the greater the
viscosity
The more viscous the magma…
the harder it is for gas to “bubble” out, so gas pressure builds up
Less viscous magmas allows…
gas to easily escape (less pressure)
Magma viscosity is also related to
magma composition
Silica-rich magmas (rocks) are…
viscous
silica-poor magmas are…
less viscous
The most explosive volcanoes have…
low-temperature magmas with abundant silica (e.g.,
rhyolite magma)
Magma composition is related to…
volcano type
Silica-rich magmas are associated with…
composite volcanoes
Silica-poor magmas are associated with…
shield volcanoes and hot
spots
Hot spots are…
stationary plumes of magma that can be used to track the motion of
tectonic plates
The ages of the volcanoes produced from a hot spot…
progressively get
older the farther you get from the hot spot
