Volcanic hazards

Nuee ardente - Part of pyroclastic cloud, very destructive, very fast. Cloud of gas, ash & magma - a mass of gas enveloped particles

Basaltic lava - low in silica, low visocity, fast flowing. 950 degrees. Forms shield volcanoes

Andesetic lava - 60% silicon dioxide. High acidity - slow moving. Forms composite volcanoes. At destructive plate boundaries

Tephra - rock fragments ejected in a volcanic eruption 

Viscocity - measure of a fluids resistance to flow - internal friction of a moving liquid

Effusive eruption - (Basaltic) lava steadily flows onto ground

Explosive eruption - (Andesetic) lava violently expelled, pressure from trapped dissolved gases

VEI: (Volcanic explosivity index) 0 = eruption not explosive - doesnt count lava flow. Could have 1VEI but still have major disruption (quantitative data)

Shield volcano

constructive plate boundaries, low gentle sloping. Basatic lava. Frequent but gentle eruptions. 

Composite volcano

 made of alternative layers of lava and ash. Destructive plate boundaries. Eruptions could br pryoclastic or lava flow.

Pyroclastic flow - dense destructive mass of ash lava and gas. ejected explosively (700km/h) flow 400 degrees.

Lahar - mudflow composed of pyroclastic material (debris, water, ash)

Volcanic acid rain - rain water through volcanic emissions (high in sulphur, lower than 4 pH)

Volcanic bomb - lava ejected from volcano solidifying in air

Volcanic gases - trapped in cavities, dissolved in magma (sulphur dioxide, hydrogren sulphide)

(refer to areal extent of hazard and hazard intensity)

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Tsunami formation: Most common cause - shallow focus earthquakes

tsunami generated by vertical displacement of water

- wave length 100m , height 1m , speed 700km/hr

Friction generated due to decreasing sea bed level, causes tsunami to slow down, 

drawback - reduction in sea level (used to detect tsunamis, seen at coast)

V causes wave to get upto 25m tall, reduces in length. 

Can go 500m inland. 90& of tsunamis are generatred in Pacific Basin

Tsunami characteristics when inland based on: 1. Coastal physical geography. 2. Length of event (at source) 3. Height of waves / distance they travelled