Volcanoes Flashcards
Where in the world do volcanoes occur?
- along the coast lines
- lots of anomalies scattered around the oceans
- around the edge of the Pacific Ocean (pacific ring of fire)
- hardly any in middle of big land masses
- found at constructive and destructive plate margins
Why do volcanoes occur at destructive and constructive plates?
This is either due to subduction which causes pressure melting of past crust which rises up through the surface (destructive) or pressure where the plates move apart is low so magma rises (constructive)
Why are there some anomalies ?
Mantle plumes (areas of rising hot magma), which causes melting of material in the lithosphere which rises through fissures and causes volcanoes
Why do we get chains of volcanoes e.g. Hawaii
As the plates are constantly moving so little volcanoes keep forming… these become dormant as don’t erupt
What are the 2 types of volcanoes?
Shield
Composite (cone)
Features of shield volcanoes (constructive boundaries)
- gentle slopes and a wide base
- frequent eruptions of basic lava
- lava flows at high speeds and long distances before cooling
- usually non violent eruptions
- non viscous lava due to basaltic composition (runny)
Features of composite volcanoes (destructive boundaries)
- steep sided with distinctive cone shape
- tall with a narrow base
- explosive eruptions of lava and ash
- viscous Lava builds in layers and does not flow far from crater
- eruptions occur less frequently
What is meant by magma viscosity
Low viscosity = thin magma = flows further and quicker
High viscosity = thick magma = flows shorter distances and slower
What effects how viscous magma is?
How much Silica makes up it:
Less silica = low viscosity (gas can easily escape, foam doesn’t form)
More silica = high viscosity (gas can’t easily escape, foam forms)
What are the 6 eruption characteristics (from small to large)
Icelandic
Hawaiian
Strombolian
Vulcanian
Pelean
Plinian
What does the VEI measure
Measures the explosively, volume of ash and height that the ash cloud reaches into the atmosphere
What other information does the VEI show
Gives a description of the eruption, the name of it, and the total number of those eruptions in human history… also allows for comparisons to be made
What is the scale of VEI
0-8
What are primary effects
Occur immediately along with the event
What are secondary effects
Direct consequence of the event but not immediate
What is a Lahar
A mixture of hot and cold water and rock fragments which flows down the steep side of a volcano
How do Lahar’s form
They form when erupted volcanic material gets saturated during periods of heavy rain. This does not have to be during or immediately after an eruption but may by some time afterwards. Although they may only start small lahars grow as they travel, picking up material as they move down the flanks of the volcano. As a steep slope is required these events are most common on stratovolcanoes due to their greater gradients
How are gases a hazard caused by volcanoes
Eruptions release large quantities of gas e.g. sulphur dioxide and carbon dioxide. They are hazardous to human health, can cause respiratory problems and even death. These gases go into the air and can cause short term effects on the climate
E.g. massive release of gas occurred in lake Nyos which is a volcanic crater lake
What are Nuees ardentes, and how are they they a hazard caused by volcanic eruptions?
‘Glowing cloud’. A fast moving cloud of hot as and ash erupted from a volcano. Fiery red. Form during explosive eruptions as erupted material collapse. They flow down into valleys at speeds of up to 50 mp. They are usually accompanied by large rocks/bounders.
E.g. 1980 eruption of St.Helens
What are mudflows, and how are they a hazard?
A form of mass movement involving the fast moving flow of debris,dirt that has been liquified. Travel up to 5m/s. They contain lots of clay so travel long distances. They can have multiple triggers such as heavy rain flow, snowmelt. They form on volcanoes after an eruption when new, loose, volcanic sediment is formed on the steep slopes is formed on the steep slopes. They can carry cars, trees, even houses. Damage water supplied, gas, waste, and electrical infrastructure.
What is pyroclastic flow and how is it a hazard?
Dense, fast moving flow of solidified lava pieces expelled from a volcano during eruption. Occurs when material begins to move down the side of a volcano. Also, when a lava dome collapses on itself as it becomes too steep. They move at up to speeds of 200m/s so are impossible to escape from. Cause secondary flooding as lava block streams
What is acid rain and how is it a hazard?
Any other form of precipitation that is unusually acidic, meaning it has elevated levels of hydrogen ions. Acid rain has a ph level lower and the more acidic the rain is, the lower the ph. It effects freshwater supplies, soils, trees, human health, weathering of stone buildings
What is ash fallout and how is it a hazard?
It falls to the earths surface from an eruption cloud. Ash and tephra is sent up into the air at incredible heights. The violent ejection contains small fragments of glass ad rock. It can travel many kilometres. Ash can cause health problems, contaminate water and lead to the collapse of structures.
What is tephra and how is it a hazard?
Rock fragments and particles ejected by a volcanic eruption grain sized). Airborne fragments are often referred to as pyroclasts. Once these clasts have fallen to the ground, they remain as tephra.
Hot tephra can trigger fires if they fall on ignitable material. Reduces visibility, danger for drivers. Drinking water may also become contaminated by fluorine from tephra
