Volcanic Hazards Flashcards
What is a Lahar/mudflow ?
Mudflow composed of pyroclastic material and water that flows down from a volcano, usually along a river valley.
How does a Lahar/mudflow form ?
Unconsolidated volcanic ash and rock from a recent eruption combined with water and can be swept down river valley in the form of a hot fast-moving mudflow. They can be caused by torrential rain in monsoon climates or ice melting from lava in colder climates.
Define vulcanicity
Refers to the rising of molten magma or other gaseous materials beneath the earths crust into the surface
Explain the nature of vulcanicity
The forms, characteristics and behaviour of magma rising
-Type of eruption
-Type of volcano
-Type of lava
Define basaltic lava
- Has a low viscosity due to low silica content
-Produces gently sloping landforms
-Frequent but gentle eruptions releasing lava and steam
-Found at constructive plate margins
Define acidic lava
-Viscous due to high silica content
-Produces steep-sided features (e.g composite volcanoes)
-Less frequent eruptions but more violent (build up of gas as can’t bubble)
-Eject gas, ash, rocks and lava
-Occur at destructive plate margins
Explain an explosive eruption
-Lots of gas trapped in magma(forms a lava dome), builds pressure until eruption
-Form pyroclastic flows
-Phreatomagnetic eruptions are explosive eruptions through water
Explain an effusive eruption
-Magma that has a low viscosity lets gas escape leads to gentle eruptions
Explain a fissure
When 2 plates move apart lava can be ejected through fissured.
Basaltic lava forms huge platuex, filling hollows
Explain a basic/shield volcano
Lava flows out of a central vent and can spread over wide areas before solidifying.
Results in a cone shape with gentle sides
Acid/dome volcano
Acid lava quickly solidifies so produces a steep sided convex cone as lava solidifies near the crater
Ash and cinder volcano
Ash and cinders from explosive eruptions build up in layers into a cone
Composite volcano
Larger, classically shaped volcano.
Result from alternative types of eruption in which first ash then lava.
Caldera volcano
When the build up of gas becomes extreme, huge explosions clear the magma chamber beneath the volcano and remove the summit of the cone. Causes the crater to subside, thus widening and opening it to several km.
Explain a Nueés Ardentes
Pyroclastic flow
-Bubbles in the magma burst explosively to eject lethal hot gases and ash, pumice and glass
-Surge downhill due to heavy rocks and dust making it dense
-Most dangerous when crater is blocked by viscous lava
-Little warning and kills ppl immediately
What is a lava flow ?
- magma flowing out of a volcano
-Fluid lava flows are hotter and move faster than viscous lava
-Burn down vegetation and structure
-Most lava flows can be avoided on foot (cm/hr acidic, km/hr basic)
Explain how gases are a volcanic hazard
-Magma contains dissolved gases which are released during eruption and when magma reaches surface
-Most abundant is water vapour. Others : CO2, Co, Cl, F, sulfur oxides
-Damages skin, eyes, respiratory system
-Can lead to acid rain (sulfur oxides)
Explain a tephra
Ash fall
-Fragmented material ejected by volcano
-Heavier particles fall closer to crater
-Hot enough to spontaneously combust and start fires
-Ash clouds can be blown miles
-Ash blankets contaminate farmland and poison livestock
-Weight of ash can cause damage
-Can cause a Lahar (mudflow)
