5 - What are the main hazards of volcanoes

Question 1

Describe Tephra and Ash as a hazard.

Answer 1

• Volcanic eruptions generate fragments of rock that are produced when magma or rock is explosively ejected - hazard much more significant from explosive eruptions compared to effusive.
• ‘Tephra’ is used to describe all erupted rock regardless of size, while the term ‘ash’ describes particles of less than 2mm in size.
• Once ash/tephra have fallen to the ground they remain as loose particles.
• Finer material can be ejected into the upper atmosphere by explosive / rhyolitic magma eruptions (VEI 6 and above) reaching the stratosphere where the particles reflect sunlight back out to space reducing insolation.

Question 2

Describe lava flows as a hazard

Answer 2

• Flows of magma extruded onto the surface of a volcano
• Occur when lava is erupted from a volcano and then falls down the side
  Far more dangerous in effusive eruptions since lava is runnier so moves faster and covers greater distances
• Generally not very deadly as slow moving so people can get out the way
• Lava can keep spewing out months after an eruption, and thick lava can take years to cool

Question 3

Describe pyroclastic flows as a hazard

Answer 3

• A combination of very hot gasses (500C+), ash and rock fragments travelling at high speed.
• Follow the contours of the landscape and destroys almost anything in its path
• Inhalation of these gasses which are so hot and poisonous causes almost instant death.
• Most commonly associated with subduction-zone volcanoes on convergent plate boundaries.
• Can extend up to 40km from its source
• Stay close to the ground as the materials in it are denser than air
• The upper part is made of gasses and smaller debris, while the bottom is a jumble of chaotic lava rocks.
• Last anywhere between a few seconds to a few hours.
• Move up to 200m/s

Question 4

Explain gas emissions as a volcano hazard.

Answer 4

• Volcanoes emit a wide range of toxic gases, including CO, CO2, and SO2. These can be deadly for humans
• Volcanoes produce gas emissions through both explosive and effusive eruptions, as the gases are expelled from the magma and into the air.
• Both explosive and effusive eruptions can produce gas emissions but explosive eruptions would expel the gas further
• Gas emissions can remain in the atmosphere for varying time depending on the size of the eruption

Question 5

Explain jokulhlaups as a hazard of volcanoes.

Answer 5

• Volcanic eruptions beneath an ice field or glacier cause rapid melting.
• During an eruption, vast quantities of water accumulate until they find an exit from under the ice.
• The resulting torrent of water can cause devastating floods.
• Water transporting rocks, gravel and blocks of ice.
• Emerge from hydrostatically sealed lakes with floating levels far above the threshold.

Question 6

Explain lahars as a hazard of volcanoes

Answer 6

• Lahars are a type of mud flow that occur after a volcanic eruption
• They have the texture of wet concrete
• They occur when liquid mixes with volcanic debris
• This can be when snow and ice near the summit of volcanos melts during an eruption or when crater lakes collapse and cause a flow down the side of volcanos
• This water mixes with ash, fragments and particles of rock, and soil, leading to the formation of a sludge
• This flow can travel at speeds of up to 50km/hr and destroys or buries obstacles in its path

Question 7

Explain Tsunamis as a volcanic hazard.

Answer 7

• Violent eruption of some island arcs can trigger tsunami waves by the huge displacement of water form the ocean
• They can also occur when lahars or pyroclastic density currents into surrounding water
• Tsunami waves can travel at 600km/hr
• As they approach the shore, they increase in height; when they break they release huge amounts of energy
• When lava meets water it expands by 70% due to cooling

Question 8

What are examples where Tphra and Ash were a major hazard

Answer 8

• Pinatubo 1991 (volcanic ash went around the globe several times causing a cool period for 3 years)
• Iceland 2010 stopped flights for 5 days

Question 9

What is an example where lava flows were a major hazard

Answer 9

Hawaii (2018)
Lava flows destroyed 1,839 structures and damaged 90 more in total

Question 10

What are examples of when pyroclastic flows were a major hazard

Answer 10

• Volcan de Fuego in Guatemala 2018 killed 60 people
• 1902 eruption of Mount Pelee was the longest recorded pyroclastic flow and killed 30,000 people

Question 11

What is an example of when gas emission were a major hazard

Answer 11

Mount Pinatubo 1991

Question 12

What is an example of when Jokulhlaups were a major hazard

Answer 12

Iceland 2010 as several volcanoes lie under the Vatnajohull ice field

Question 13

What are examples where Lahars were a major hazard

Answer 13

• Nevado del Ruiz (1985)
  
  • Killed thousands due to poor land use zoning
• Gahinggung (1983)
  
  • Killed 35,000 and buried 90,000 ha of crops

Question 14

What is an example of when Tusnamis were a major volcanic hazard

Answer 14

• Hunga Tonga eruption in 2022: caused at least 4 deaths. Slightly higher waves in Peru and Japan but not dangerous.