Volcanic Hazards Flashcards
What is lava?
Molten rock above the surface
What is magma?
Molten rock below the surface
What differs in lava?
Viscosity
What is viscosity?
How thick the lava is
What 2 things control viscosity of lava/magma?
Temperature
Composition of magma
What is the viscosity of the lava at constructive boundaries?
High temperature
Low silica content
What is the viscosity of the lava of destructive boundaries?
Lower temperature
High silica content
What are effusive eruptions?
Where lava pours out of a volcano freely
When do effusive eruptions occur?
When the lava is low viscosity
What type of lava is at effusive eruptions?
Basaltic
Where are effusive eruptions found at?
Constructive plate margins
What are explosive eruptions?
Where lava doesn’t escape easily and volcano explodes
When do explosive eruptions occur?
Where lava is viscous and doesn’t flow freely
What type of lava is at explosive eruptions?
Andesitic
Where are explosive eruptions found at?
Destructive plate margins
What is basalt lava?
Lowest silica content
Low viscosity
Flows a long distance
Associated with effusive eruptions
What is andesite lava?
Higher silica content
Higher viscosity
Flows a shorter distance
Associated with explosive eruptions
What is rhyolite lava?
Highest silica content
Higher viscosity
Doesn’t flow far at all
Associated with explosive eruptions
Why do lavas behave differently?
Due to composition and viscosities
What is tephra?
Solid material that varies in size from volcanic bombs to ash
Why are low viscosity lavas not hazardous?
Can flow for long distances but tend to be slower so not hazardous
Why are pyroclastic flows hazardous?
Very hot and one of the deadliest hazards of volcanoes
What are pyroclastic flows?
A mix of gas and tephra - very hot and moves at speeds up to 700km an hour
Why are volcanic gases hazardous?
C02, chlorine, Carbon monoxide and sulphur dioxide plus fluorine are all present
What are lahars?
Unconsolidated ash from a recent eruption combined with water which may have be swept down river valleys in the form of a hot,dense,fast-flowing mudflow.
What does lahars form?
A debris flow composed of water, ash and rocks
How is climate change hazardous?
Gases have a large effect on climate
What is VEI?
Volcanic Explosively Index
