Hazards - Volcanoes Flashcards
At what 4 places is volcanic activity found?
Oceanic ridges
Rift Valleys
Subduction Zones
Hot spots
How are the 2 different types of volcano?
Shield
Composite
What are shield volcanoes?
Big volcanoes made from layers of solidified balsatic lava with gently sloping sides
What are composite volcanoes?
Smaller volcanoes made of alternating layers of andesitic lava and ash with steep slopes above 10 degrees
What types of volcanoes form at destructive boundaries?
Composite
Where do shield volcanoes form?
At constructive boundaries or hot spots
What kind of eruptions do composite volcanoes do?
Explosive
What kind of eruptions do shield volcanoes do?
Effusive
What is a volcano?
An opening in the crust of the Earth connected underground to a magma chamber from which molten lava, gases, steam and pyroclastic material are ejected.
What impacts the shape and form and type of eruption of a volcano?
Its lava
What is the difference between effusive and explosive eruptions?
Explosive is arbourne
Effusive is landbound
What is tephra?
Explosive material under 64mm
What is a volcanic bomb?
Explosive material over 64mm
What is the Benioff zone?
Part of the subduction zone where oceanic plate melt into magma
How do volcanoes form in rift valleys?
The crust in rift valleys is much thinner than in neighbouring areas. Magma forces its way to the surface through the thinning crust
What are hot spots?
Small areas of the Earth’s crust where an unusually high heat flow leads to volcanic activity
How do volcanoes form over hot spots?
Column of upwelling magma melts the overlying crust and molten magma is forced through the crust. The plate moves over the hotspot, forming a succession of volcanoes.
How can volcanoes that are not directly above hot spots still erupt?
As the plate moves it drags the head of the magma plume with it
What is the main method of measuring the magnitude of volcanic eruptions?
Volcanic explosivity index
What percentage of volcanoes lie on plate margins?
95%
What are active volcanoes?
Volcanoes that have erupted in the last 2,000 years
What are dormant volcanoes?
Volcanoes that haven’t erupted in the last 10,000 years
What are extinct volcanoes?
Volcanoes that aren’t going to erupt again
What percentage of the Earth’s surface is made of silica?
95%
What are the primary hazards of volcanoes?
Tephra Pyroclastic flows Nuee ardentes Lava flows Volcanic gases
What are the secondary hazards of volcanoes?
Lahars Acid rain Flooding TSunamis Volcanic landslides Climate change
What are pyroclastic flows?
Very hot gas charged high velocity flows made up of a mixture of gas and tephra that flow down the sides of the volcano
What are lahars?
Mud flows formed by the combination of melted snow and ice and volcanic gases, which quickly move down the course of river valleys
How do volcanic eruptions cause flooding?
Eruptions melt glacier and ice caps
How do volcanic eruptions cause acid rain?
Eruptions emit sulphur dioxide which combines with atmospheric moisture to form acid rain
What type of lava do shield volcanoes have?
Basic, non-viscous
What type of lava do composite volcanoes have?
Acidic, viscous
Are shield or composite volcanoes hotter?
Shield
What percentage of silica is basic lava?
45%
What percentage of silica is acidic lava?
66%
