Describe the types of volcanoes that occur at Constructive margins & hotspots.
-SHIELD VOLCANOES
•produced by very hot (1200) and low in viscosity basaltic lava
•long time to cool and fast moving thus flatter sides
•not very explosive as low in silica
•high frequency but low magnitude
•possibility of damage if high housing density (hawaii)
Describe the volcanoes that occur at destructive plate margins.
-CONE VOLCANO •cooler andesitic lava (800) with high viscosity, therefore flows less easily and less far •highly explosive •high magnitude and low frequency •allows time for gas to build
Products of volcanoes: describe a pyroclastic flow.
Pyroclastic flow:
•fast moving current of hot gas and tephra
•reaches up to speeds of 700km/h and temp of 1000c
•caused by collapsed eruption column from plinian eruption where material ejected from vent heats surrounding air
NUEES ARDENTES
- turbulent cloud of gas ash and rock fragments flowing close to the ground
- extremely dangerous and unpredictable
TEPHRA
- pyroclastic materials deposited by falling through the air
- all explosive eruptions make this
- largest (bombs) are deposit near vent
Products of volcanoes: Lava flows.
- between 550-1400
- slow moving
- can melt snow/ ice causing flooding
- destroys property
Products of volcanoes: Mudflows/ Lahars
- type of mudflow containing pyroclastic material
- fast moving and can erase virtually anything in its path
- prediction is hard as it’s capable of carving its own path
- caused by number of reasons, most commonly pyroclastic flows during an eruption
Products of Volcanoes: Volcanic landslides, Ash fallout and gases.
volcanic landslides:
•common on volcanic cones because they’re gradient
•large masses of rock and soil that flow rapidly under the force of gravity
•caused by volcanic gases partially dissolving in groundwater, weakening the rock by altering minerals
•cause lahars
