p4 Flashcards
What’s a volcano?
Like earthquakes, volcanoes are closely related to plate margins as they are areas in the Earth’s crust through which lava, ash and gas can erupt.
Small numbers occur on hotspots.
Volcanoes get bigger as more and more eruptions occur. Lava cools to form rock after each eruption and builds over time.
Over the past 300 years, approximately 260,000 people have died as a result of eruptions.
Primary Hazards of volcanic eruptions
Lava Flows
Pyroclastic Flows
Tephra and Ash Falls
Gas Eruptions
Lava Flows
These are streams of lava that have erupted onto the Earth’s surface.
They can reach up to 1170˚c (hot!) and take years to cool completely.
Due to their heat they destroy everything in their path.
However, they are generally not threatening to humans as most of them move slowly as people can move out of their way.
Pyroclastic Flows
These are a mixture of dense hot rock, lava, ash and gases ejected from the volcano.
They can reach temperatures up to 700˚C.
They can move very quickly, up to 100km per hour (you can’t outrun it!).
Like lava, they destroy everything in their path.
Tephra and Ash Falls
Tephra are pieces of volcanic rock and ash that blast into the air during eruptions.
The large pieces tend to fall near the volcano where they can cause injury or death (as well as damage structures). The smaller pieces (ash) can travel for thousands of kilometres.
Ash falls can be very disruptive as it covers everything causing poor visibility and slippery roads. Roofs may collapse under the weight and engines may get clogged up and stop working.
Gas Eruptions
Magma (lava that hasn’t reached the Earth’s surface) contains dissolved gases that are released into the atmosphere during eruptions.
These gases include water vapour (around 80%), carbon dioxide and sulphur dioxide.
Once the gases are in the air they can travel for thousands of kilometres.
Some gases can be potential hazardous to people, animals and structures.
Secondary Hazards
Lahars
Jӧkulhlaup
Lahars
These are masses of rock, mud and water that travel quickly down the sides (flanks) of a volcano.
They vary in size and speed. The largest can be hundreds of metres wide and can flow at tens of metres per second (too fast to outrun!)
They are caused when an eruption quickly melts snow and ice OR when heavy rainfall has occurred either during or after an eruption and has eroded rocks and soil, causing it to become lose and surge downslope.
Jӧkulhlaup
Pronounced yo-KOOL-lahp (otherwise known as glacial outburst floods).
These are when the heat of a volcano melts the snow and ice in a glacier causing heavy and sudden floods.
These can suddenly release large amounts of water, rock, gravel and ice that can be extremely dangerous as they can flood and damage land and structures.
Predicting Volcanoes
Unlike earthquakes, scientists can often predict eruptions with some accuracy.
Scientists use equipment (GPS and satellite-based radar) placed on and around a volcano to monitor the signs:
Small earthquakes – as magma rises it breaks rock, causing small earthquake, which can be detected on seismograms.
Changes to the surface of the volcano – magma builds pressure, causing the surface of the volcano to swell.
Changes to the ‘tilt’ of a volcano – moving magma inside can change the slope angle or ‘tilt’.
However, not all predictions are accurate and not all are monitored!
Eyjafjallajӧkull Eruption, Iceland
Background info:
Iceland has several volcanoes and is situated on two tectonic plate boundaries – the North American plate and the Eurasian plate.
The volcano, situated on the Eastern Volcanic zone in southern Iceland, began erupting lava on 20th March 2010. At first there was not much explosive activity. A second eruption then began beneath the ice cap near the summit of the volcano on 14th April 2010.
Eyjafjallajӧkull Eruption, Iceland
Impacts
The eruption in April lead to the interaction of magma and water which created a plume of very fine volcanic ash and gas over 33,000 feet high, which spread and was carried south eastwards over western Europe. Jӧkulhlaups were also produced due to meltwater from glacier, meaning surging water at 17˚C caused flooding.
Eyjafjallajӧkull Eruption, Iceland
social
“Ash contaminated local water supplies.
700 people had to evacuate due to the lava partly melting a glacier, causing a major flood.
People living ‘downwind’ of the volcano had to wear goggles and facemasks due to thick ash.
Many roads surrounding the volcano were shut down.
Over 10 million passengers around the world were stranded or unable to board flights. “
Eyjafjallajӧkull Eruption, Iceland economic
“100,000 commercial flights were cancelled worldwide.
Worldwide, airlines lost US$1.7 billion.
The European economy lost US$5 billion.
Many different transport companies e.g. trains were able to benefit. The Eurostar for example, saw an extra 50,000 passengers.”
