Volcanic hazards

What are the seven different forms of volcanic hazards?

• pyroclastic flows (nuée ardentées)

• lava flows

• gases

• ash fallout

• lahars

• tephra

• acid rain

What are pyroclastic flows (nuée ardentées)?

burning clouds of hot rock, lava, ash, and gases

What are the characteristics of pyroclastic flows (nuée ardentées)?

• contain tephra

• move at speeds of over 500mph

• temperature of between 350° and 1,000°

What is an example of a well-known pyroclastic flow (nuée ardentée)?

Mount Pinatubo, the Philippines (1991)

• 1,000 deaths

What are lava flows?

flows of molten rock

What are the two types of lava flows?

• basaltic

• acidic

What are the characteristics of basaltic lava flows?

• low viscosity

• runny

• fast-flowing lava

• low silica content

What are the characteristics of acidic lava flows?

• high viscosity

• thick

• slow flowing lava

• high silica content

What gases are released by volcanic activity?

• carbon dioxide (CO₂)

• carbon monoxide (CO)

• hydrogen sulphide (H₂S)

• sulphur dioxide (SO₂)

• chlorine (Cl)

What is ash fallout?

erupted material ejected into the air

What are the characteristics of ash fallout?

• clouds of ash

• reduces sunlight

• reduces temperatures

• travels high into the stratosphere (30km)
  

What is an example of a well-known occurrence of ash fallout?

Mount St. Helen's (1980)

What are lahars?

boiling mud flows

What are the characteristics of lahars (mudflows)?

• temperatures of 100°C

• melting ice and snow, producing mud

• fast flowing, with speeds of up to 60km/h

• highly erosive

What is an example of a well-known lahar (mudflow)?

Nevado Del Ruiz (1985)

• 25,000 deaths

• speed of 60km/h

• town of Armero completely destroyed

What is tephra?

rock fragments ejected into the sky

What are the characteristics of tephra?

• <2mm in diameter (ash particles)

• 1m in diameter (volcanic bombs)

What is acid rain? How is it caused?

when the sulphur dioxide released by a volcano during an eruption combines with the moisture in the air

What are the characteristics of acid rain?

• dangerous for ecosystems

• raises the acidity of waters

• toxic to marine animals

• causes the weathering of buildings

• causes the corrosion of metals