Hazards Flashcards
Active Volcanoes
in the last 10,000 years, have the potential to erupt still
1,500 active volcanoes, 60 eruptions per year, 20 eruptions at any given times
Dormant Volcanoes
Have not erupted in the last 10,000 years but still could
Extinct
No chance
Primary hazards [6]
Lava flows Tephra and ballistic Pyroclastic Debris avalances Earthquakes Gas Emissions
Lava flows
880-1200, forms a skin below 800
Highly viscous 1.3km x 100m thick
Pyroclastics flows
hot gas and volcanic material; low density pumice to dense clasts. 10% solid by volume. Follows topographic lows (valleys)
Pyroclastic Surge
Turbulent, low-density, high velocity, not constrained by topography. 0.1-1% solids by volume i.e. higher gas to rock ratio
pyroclastic
10-300m/s, 100-1100 degrees C, 10s of km
Pyroclastic hazard [7]
- Health hazard e.g. respiratory
- Destruction by direct impact
- Burying sites (can result in mudflows and lahars
- Destruction by fire
- Malfunction of machinery e.g. aeroplanes
- Surface water acidity
- Climatic effects; reduced T, inc rain
Gas emissions
SO2, CO2, HF
Lake Nyos, Cameroon
3000 cattle dead, 1700 people dead, 16km of lake
Rapid degassing of CO2; 50m thick cloud. Moved down slope as heavier than air
Earthquakes
rarely exceed 5 on Richter scale
Trigger eruptions or generate landslides
Progressively shallower due to moving magma
Secondary Hazards [7]
Lahars, floods/tsunamis, fires, air pollution, disease/famine, social effect, climatic effects
Mudflows or lahars
produced in response to pyroclastic flows, interacting with severe rain, river water, crater lakes, or volcanic glaciers
Fast moving mud flow,
lahars due to glacier bursts
Fluidised hot mud flows, high altitude volcanoes and high latitudes
