Volcanic processes and the production of associated hazards Flashcards
What is a pyroclastic flow/surge?
Bubbles of hot gases and pyroclastic material that burst into clouds that can be up to 1000 degrees, and be ejected laterally at the source at 30 m/s. They are responsible for the most deaths and result from frothing of the magma in the vent
What are lava flows?
Lava flowing out of a fissure, vent or crater and coming straight down the slope side. It is mostly a threat to property, Kilauea lava covered 78km in every direction, destroying 200 houses in its wake. The most dangerous come from fissures, which travel downhill at 50 km/h. Pahoehoe lava is the most liquid and forms a ropey wrinkled surface wherever it sits.
What is airfall tephra?
Also known as ash clouds - fragmented material that is expelled out of the volcano and eventually comes to land around the volcano. Mt St Helens ejected an estimated 6 km cubed of material, with particles from >32m in diameter to <4mm in diameter, with the cloud also hot enough to combust and start fires.
What was significant about the 1816 Tambora eruption?
Tambora in 1816 led to short-term global cooling of 1-2 years due to the global ash cloud.
What are the issues with airfall tephra?
It can blanket the landscape, poisoning farmland, water and livestock.
Health issues such as skin abrasion and breathing problems, and the weight of it can damage structures.
What are the 4 main volcanic gases?
Hydrogen, carbon monoxide, hydrogen sulphate and sulphur dioxide.
What was the impact of volcanic gases following the Mt Merapi eruption?
As Indonesian villagers evacuated, they walked into a dense pool of CO2 - 140 asphyxiated.
Water resources also were unusable, as there was unusually high levels of CO2 in the water - it had been sequestered but in a contained lake it absorbed too much to be potable.
What are lahars?
Volcanic mudflows of silt-sized sediments. Ash and rock create a vicious flow with rainwater - this is prevalent in SE Asia - Mt Pinutubo in Philippines has a lahar that is over 10M m3, and has been known to destroy farmland, property and occasionally take lives.
How are lahars simultaneously primary and secondary hazards?
Primary - sediment effuses out of the fissure and immediately begins its fall downhill.
Secondary - ash clouds settle, get rained on, and become a lahar.
What are volcanic landslides?
A common feature associated with siliceous, acidic magma with high viscosity. Mt St Helens collapsed in 2004, released 1.7 km2 of material into the atmosphere, triggered by heavy rainfall and earthquakes. Ground deformation due to rising magma bulges on the slopes can also create landslides pre-eruption, and the sudden loss of pressure on that particular area can cause an eruption.
What are Jokulhalaups?
Subglacial eruptions when there is meltwater trapped in a GLOF between the volcano and glacier. Grimsvot in 1996 had 3.2km3 of water drain in 40 hours, causing 14M worth of damage and leaving icebergs all over the Icelandic landscape.
