Volcanic Hazards Flashcards
What lava is found at a constructive plate margin?
Basaltic lava.
Is basaltic lava runny?
Yes it has a low viscosity, so it flows easily and quickly.
Are eruptions of basaltic lava frequent and violent?
They are frequent and go on for a long time, but they’re not very violent as gases are able to escape easily.
What type of lava is found at a destructive plate margin?
Andesitic and rhyolitic lava
Is the lava runny?
It is less runny than basaltic lava, so they flow less easily.
Are eruptions of andesitic lava frequent and violent?
They usually erupt every once in a while and the eruptions are short lived.
What does the andesitic lava cause?
It forms blockages in volcanic vents, causing pressure to build. The blockage is cleared by a violent eruption.
What type of volcano does andesitic lava form?
A stratovolcano
What type of volcano does a basaltic lava form?
A shield volcano.
What is a pyroclastic flow?
- A pyroclastic flow is a mixture of super-heated gas, ash and volcanic rock that flows down the sides of a volcano. It travels at high speed (often more than 80km/h) and flows a long way (generally around 10-15km).
- Because they travel fast and can happen with relatively little warning, pyroclastic flows can cause widespread death and destruction, through e.g. burning and burial under debris.
What is a lava flow?
- Lava can flow from a volcanic vent down the side of the volcano.
- The speed of the flow and the distance travelled depend on the temperature and viscosity of the lava, as well as the steepness of the slope- low viscosity (runny) lava can flow at up to 10km/h on a seep slope and may travel tens of kilometres.
- Most flows are relatively slow, so people have time to evacuate areas that will be affected. However, lava flows destroy anything in their path, including buildings and vegetation, by burning, burying or knocking it down.
What is a mudflow?
• Mudflows occur when volcanic material mixes with large amounts of water (e.g from rainfall or from ice melted by the eruption). Flows move very quickly (over 80km/h) and can travel for tens of kilometres. Mudflows can bury or destroy natural habitats, settlements and infrastructure.
What is a pyroclastic and ash fallout
- Pyroclastic fallout is material that has been ejected from volcano during an eruption and falls back on the ground. When fallout consists of mostly ash, its called ash fallout.
- Fallout consists of material of a range of sizes- from large pieces of rock weighing several tonnes to microscopic ash particles. Material can travel thousands of kilometres from the volcano. Heavier particles are deposited earlier than light ones, so material ends up being well sorted, with larger, heavier particles deposited near the volcano and smaller, lighter particles further away.
- Large pieces of falling tephra can damage buildings and kill or injure people. Finer material can from a layer up to several metres in thickness, which can kill vegetation, hinder road and rail transport and cause buildings to collapse. Ash can also be harmful to people if its breathed in.
What type of gases are released during a volcanic eruption?
Lava contains gases such as carbon dioxide and sulphur dioxide which are released into the atmosphere when a volcano erupts. Some of these gases can be harmful to humans and animals if they’re breathed in, e.g. sulphur dioxide can cause breathing difficulties.
