Tectonic Backgroud Revision Flashcards
Physical hazard profile- magnitude
-most important influence on the severity of tectonic hazard.
-measured by the MM scale
-MM is based on a number of parameters
Physical hazard profile-frequnecy
-Frequency is how often an event occurs
-Inverse relationship between frequency and magnitude, i.e. the larger the magnitude the less frequent its occurrence.
-Areas that experience frequent tectonic events have both adaptation, monitoring, education and community awareness, and mitigation measures in place
Physical hazard profile- duration
-This is the length of time for which the tectonic hazard exists.
-Secondary hazards often prolong the duration of impact and increase the damage
Physical hazard profile-Speed of onset
-The speed of onset and the almost immediate shaking of the ground led to the maximum destruction
Physical hazard profile- predictability
-Gap theory can increase the possibility of prediction
Tell me about Strato volcanoes
-Alternating layers of lava and ash resulting from eruptions at destructive margins.
-Lava is acidic with 50% silica content. (Silica causes multiple diseases)
-Ash produced at high exposity
Tell me about Pyroclastic flows and surges
- result from frothing of the molten magma in the volcano vent
-Bubbles in the magma burst explosively to eject a lethal mixture of hot gases and pyroclastic material (volcanic fragments, ash, pumice and glass shapes)
-Contains heavy rock fragments and dust.
-Clouds may be red hot, up to 1000 degrees celsius.
-Little warning of these events.
Tell me about lava flows
-Dangerous lava flows come from fissure eruptions.
-A’a lava forms blocks and moves slowly down the hill.
Tell me about volcanic gases
-Complex mixture of gases include water vapour; hydrogen; carbon monoxide; carbon dioxide etc
-Carbon monoxide causes deaths because of its toxic effects at low concentrations.
-More deaths associated with Carbon Dioxide
Secondary volcanic hazards- lahars
-they are volcanic mudflows composed of largely silt-size sediments.
-consist of volcanic ash and rock combined with the torrential rain
-create dense, viscous flows that can travel even faster than clear- water streams.
-can be classified as primary, occurring directly during a volcanic eruption and secondary which are triggered by high intensity rainfall between eruptions
Secondary Volcanic Hazards-landslides
- associated with eruptions of siliceous magma of high viscosity with a large content of dissolved gas.
-Volcanic landslides are gravity driven slides of masses of rock and loose volcanic material
Secondary Volcanic Hazards-Jokulhlaups
- In subglacial eruptions, the water produced from melting ice becomes trapped in a lake between the volcano and the overlying glacier.
-Eventually, this water is released as a violent and dangerous flood.
Primary Effects of earthquakes-Ground movement and ground shaking
-Initial effect of an earthquake is ground shaking.
-Severity will depend upon the magnitude, duration, the distance from the epicentre, the local geological conditions of the area, quality of buildings e.g. poorly built, unreinforced structures with heavy tiled roofs.
Secondary Effects of earthquakes
-Soil liquefaction
-when violently shaken soils with a high water content lose their mechanical strength and start to behave like a liquid.
Secondary effects of an earthquake -define Landslides / avalanches
slope failure as a result of ground shaking.
