Volcanoes

• The measurement of volcanoes intensity is the VEI (Volcanic explosivity index. It rages from 0 to 8, with 0 being non-explosive and 8 being mega colossal.
• The distribution of volcanoes is that of linear clusters along plate boundaries. There is a high concentration of volcanic activity around the pacific ring of fire.
• Anomalies of volcanic normal distribution is hot spots. This is when plumes of magma exploit weaker crust, for example Hawaii.
• The primary hazards of volcanoes are liquids, gases and solids.
• A nuee ardente is a turbulent, fast moving cloud of hot gas and ash erupted from a volcano. They often occur after a long period of inactivity as gases build up. Volcanic gases can contain 80% water vapour, carbon dioxide, sulphur dioxide and hydrogen sulfide.
• Liquid hazards come from lava. Aa lava and pahoehoe lava is basaltic and is relatively runny. Aa lava are faster and originate from a faster eruption, they can be up to 10 meters deep. Pahoehoe lava is slower and is characterised by its wrinkly appearance, it cools slower and travels further.
• Solid primary hazards from volcanoes include pyroclastic flows, which is material from the plug that is mixed with ash and gases. Often molten material solidifies in the air.
• Pyroclastic flows are responsible for half of the volcanic related deaths. They are extremely dense and travel at 80-100 kmph and can reach temperatures of 200-700 degrees.
• Secondary volcanic hazards are lahars and volcanic landslides.
• Lahars are volcanic mud flows with a range of particle sizes, the water can be from the water vapour content, rainfall or glacier melt.
• Lahars are dense, viscous fast flows, with the more contents they have the faster and more destructive they are. They are often found with steep slopes, which allows them to pick up material and gain speed.
• Volcanic landslides can be dry or wet, but are dryer than lahars, however they can evolve into one. They can be 100 km (cubed) in volume and travel at 100 km/h.
• Volcanic landslides occur when magma forces material as it comes out of the vent, but can also occur when an earthquake erupts under the volcano. They can also trigger the eruption by removing the lid of gases and magma.
• Viscosity relied on the silica content. Silica is a natural thickener and creates viscous, slower moving lava. There is more silica nearer to the surface due to gravity drawing it up during a period when the earth was molten.
• Temperature, silica content and plate boundaries are factors effecting viscosity.
• If the lava is viscous, it creates more intense eruptions due to gas being unable to escape, meaning pressure builds.
• Plate boundary affects viscosity because it depends on how deep the origin of the lava is, which relies on the rate of subdution.