Volcanoes Flashcards
What are volcanoes?
Openings in the earths crust through which lava, ash and gases erupt.
How to volcanoes occur?
As tectonic plates move, pressure builds and hot magma and gases push up from the mantle to the earths crust - and erupt.
What is lava?
Magma once its reached the earths surface.
How many volcanoes are active today and how many people are at risk?
1,900
500 million worldwide
What are the primary hazards of volcanoes?
Lava flows
Pyroclastic flows
Tephra and ash falls
Gas eruptions
What are lava flows?
Streams of lava that have erupted from a volcano onto the earths surface.
They can reach 1170c and can take years to cool completely.
Why are lava flows hazards?
Generally not a threat to humans because most move so slowly people can get out of the way.
However, they do destroy everything in their path.
What are pyroclastic flows?
They are a mix of dense hot rock, lava, ash and gases ejected from a volcano, which move very quickly across the earths surface (100km per hour)
They’re one of the greatest volcanic hazards.
Destroy everything they touch and are extremely hot - 700c
What are tephras?
Pieces of volcanic rock and ash that blast into the air during volcanic eruptions.
How are tephras a hazard?
Larger pieces tend to fall near the volcano, where they can cause injury or death, as well as infrastructure damage.
The smaller pieces can travel for thousands of km
What are ash falls?
Where the ash lands, it covers everything
How are ash falls a hazard?
causing poor visibility and slippery roads.
Roofs can collapse under the weight
Engines can get clogged up and stop working
What are gas eruptions?
Magma contains dissolved gases that are released into the atmosphere during a volcanic eruption (some are potential hazards to people, animals and structures).
They include water vapour (80%), carbon dioxide and sulphur dioxide - they can travel for thousands of km once in the air
What are the secondary hazards?
Lahars
Jokulhlaup
What are lahars?
Masses of rock, mud and water that travel quickly down the sides of a volcano.
They vary in size and speed but can be hundreds of metres wide and can flow at tens of metres per second
How are lahars formed?
Caused when an eruption quickly melts snow and ice
Or heavy rainfall during or after an eruption erodes loose rock and soil - causing it to surge downslope
What are jokulhlaups?
The heat of a volcanic eruption can melt the snow and ice in a glacier, causing heavy and sudden floods
How can jokulhlaups dangerous?
They suddenly release large amounts of water, rock, gravel and ice that can catch people unawares, and flood and damage land and structures
What are the social, economic and environmental impacts?
Loss of life Migration to other countries - older people stay, younger go Destruction of main services/cities Loss of economy Destroyed infrastructure Huge unemployment Loss of farmland - less food/income
How do you measure volcanic eruptions?
Volcanic explosivity index (VEI)
What does the VEI do?
Describes and compares the size or magnitude of volcanic eruptions
How does the VEI work?
Uses a scale from 0 (non-explosive) to 8 (extremely large).
Its logarithmic - with each number increasing by a factor of ten
What factors does the VEI use to assign a number?
The amount and height of the volcanic material ejected (tephra and ash fall)
How long the eruption lasts
Qualitative descriptive terms (such as ‘gentle’, ‘explosive’)
How do you predict eruptions?
Unlike earthquakes, scientists can often predict eruptions with some accuracy.
How can eruptions be predicted?
Equipment placed on volcanoes as well as remote equipment (GPS and satellite-based radar) scientists can monitor a volcano for signs that it might erupt.
What are the signs of an eruption?
Small earthquakes - as the magma rises to the surface, it breaks the rock, causing small earthquakes which scientists can detect on seismograms.
Changes to the surface of the volcano - as it pushes upwards, the magma builds pressure (causing the surface of the volcano to swell)
Changes to the ‘tilt’ of the volcano - as the magma moves inside the volcano, it changes the slope angle or ‘tilt’ of the volcano.
