Hazards - Volcanic Hazards

Question 1

What is the distribution of Volcano’s?

Answer 1

• Form along divergent plate boundaries where plates move apart
• Also, along convergent plate boundaries or near subduction zone e.g. the Pacific Ring of Fire
• Also, over Magma Plumes/hotspots e.g. Mauna Loa in Hawaii

Question 2

What is the frequency and magnitude of Volcano’s?

Answer 2

• The more frequent a volcanic eruption the less likely it is to be higher in magnitude
• Frequency can be determined by looking at past eruptions and use deposits from the volcano

Question 3

What are the primary impacts of volcanic hazards?

Answer 3

• Tephra – varying material ejected into air + atmosphere that can block sunlight cooling the earth
• Pyroclastic Flows – high velocity flows made up of gas + tephra’s that flow down volcano (up to 700km) which destroyed Pompeii
• Lava Flows – low velocity but are unstoppable and will go through anything
• Volcanic Gases – include gas like CO2 + SO2 – 1986 Lake Nyos in Cameroon killed 1,700

Question 4

What are the Secondary Impacts of volcanic hazards?

Answer 4

• Lahars (Mudflows) - ash mixed with water may flow quicky down river valleys after heavy rain
• Flooding – Eruptions can melt nearby glaciers causing serious flooding
• Tsunamis – waves generated by strong volcanic eruptions e.g. 2004 Boxing Day
• Climate change – ash in atmosphere can block out solar radiation causing colder temperatures

Question 5

What are the responses to Volcanic Hazards?

Answer 5

Preparedness:
Many volcanos are monitored by observatories or satellites, signs that an eruption could occur include = increase in gases released, rise in lava level in crater, increasing number of small earthquakes indicating pressure build-up

Mitigation:
- Evacuation plans e.g. Monserrat 2/3 of island was an exclusion zone in 1995
- During an eruption some build trenches and use explosives to guide lava flow away from settlements

Adaption:
Areas near volcanos have extremely nutrient rich soil e.g. farmers near Mt Nyiragongo can now grow banana’s + cabbage so income has doubled since eruption in 2002

Question 6

A recent Volcanic Event - Mount Pinatubo 1991, Philippines

Answer 6

• Philippines on the pacific ring of fire, Clark American air base and city of Angeles at the base (high vulnerability)
• Primary effects - Due to previous small eruptions evacuation was effective, only 6 people died initially, ash destroyed crops + 150,000 homes (ash covered 800km)
• Secondary effects – water supplies contaminated, due to rainfall + dangerous lahars (rising death toll to over 800), over 800,000 livestock died through starvation for lack of grass and asphyxiation, food shortages + crop failure led to 3% decline in GDP, ash blocked sunlight lowering temp.