Volcanoes

DEFINITION = An opening, or rupture, in crust, which allows hot magma, ash and gases to escape from below the surface

Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface.

Volcanoes are situated on plate boundaries - mainly destructive and constructive margins - most around Pacific Ring of Fire

Volcanoes cause fewer fatalities than earthquakes, hurricanes and famine

Volcano Features:

Magma Chamber: the pocket beneath a volcano where magma collects

Pipe: a long tube through which magma moves from the magma chamber to Earth’s surface

Vent: the opening through which molten rock and gas leave a volcano 

A dike forms when magma hardens into a vertical crack

A sill forms when magma hardens into a horizontal crack

A laccolith is an igneous intrusion  that has been injected between two layers of sedimentary rock. 

A batholith is a large emplacement of igneous intrusive rock that forms from cooled magma deep in the earth's crust.

How volcanoes erupt

When magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it as to how it erupts.

• Large amounts of gas and a high viscosity (sticky) = magma will form an explosive eruption
  • When magma has cooled to make a lava plug blocking a crater, the plug traps hot gas and magma under the ground
  • Hot gas builds up until the pressure becomes too great. 
  • Hot gas and magma explode out of the volcano in a shower of dust, ashes, cinders, and volcanic bombs
  • Have high silica lava (e.g., rhyolite), 
  • Explosive volcanic eruptions can be catastrophic
  • Erupt 10’s-1000’s km3 of magma
  • Can send ash clouds >25 km into the stratosphere

• Small amounts of gas and (or) low viscosity (runny) = magma…