4.4 - Volcanic Hazards Flashcards
What are volcanic hazards?
There can be a wide variety of volcanic hazards.
Some are directly associated with volcanic eruptions (primary) and others are indirectly associated (second or tertiary)
Climatic and environmental impacts may be ongoing for many years after eruption
How have volcanic hazards impacted people of the years?
Nearly 500 volcanic events in the 20th century have impacted people.
- 6 million people have been evacuated or left homeless
- There have been up to 100,000 fatalities
- There have been a number injured (roughly 12,000) which is much less than those killed as there are low survival rates
- Fatalities have been dominated by a few large events
What are the hazards of lava flows?
Lava flows are the primary effect of volcanism
- They are particularly basaltic and can cause serious damage to properties
- They are not particularly lethal as most travel between 1-50km hr
Eg. Hawaii volcano of Kilauea began to erupt on May 3rd 2018
- There was an evacuation of around 2000 residents with 24 injures and >$800 million in damages
What are the hazards of pyroclastic flows?
Pyroclastic flows are the primary effects of volcanism
- They can move extremely fast (100-300km hr) and are extremely hot (up to 1000 degrees)
- They devastate anything in their path and cause death by suffocation and burning
Eg. On may 8th 1902, Mt Pelee (Martinique), had a large summit eruption which generated a pyroclastic flow that destroyed the town of Saint-Pierre
- 30,000 people died and there were 2 survivors = one was Louis-Augusta Cyprais who was being held in jail at the time
What are the hazards of ash clouds?
They are a primary effect of volcanism
- Ash can accumulate to form thick layers of debris which can cause roofs and power lines to collapse
- Ash buries crops, poisons soils and infiltrates machinery
- The inhalation of fine ash can cause respiratory problems
- It also poses a threat to aircrafts and an ash cloud can abrade engine parts and clog up jet engines
- Acidic aerosols etch windows so you can’t see out
Eg. Eyjafjallajokull eruption closed European airspace which cost $200 million per day
What are hazards of gas emissions?
Gas emissions are primary effects of volcanism
- The level of hazard to people will depend on the toxicity, concentration and duration of emissions
- C02 is heavier than air, at high concentration (>10%) it can cause suffocation
- S02 and H2S - combine with water vapour in the air to form sulfuric acid which is a corrosive acid - it can irritate soft tissues and damage lungs and eyes
- HF is highly corrosive and toxic, and causes terrible internal burns and attacks calcium in the skeletal system
What is an example of an eruption that produced hazardous gas emissions?
Laki eruption, 1783-1784
- There was a 32km long fissure and it erupted 14km3 of basalt lava
- It produced clouds of poisonous hydrofluoric acid and sulphur dioxide
- 50% of livestock population died
- The famine which followed killed 25% of the human population of Iceland
- Major Icelandic fissure eruptions can emit more S02 (per year) than combined industrial sources in Europe
What are the hazards of mudflows/Lahars?
They are secondary effects of volcanism
- It is the mixing of volcanic ash and debris with water = lahar
- It flows like wet concrete which is very dense/viscous but it moves fast (>50km hr) and travels far by utilising existing drainage.
- They are particularly dangerous when the volcano is covered in a glacier/snow cap
Eg. Java (Semeru volcano)
Nevado del Ruiz (Columbia) , lahars
- A snow-capped volcano erupted violently in 1985 and the eruption material melted the snow cap and formed 4 thick lahars
- One travelled down the valley toward Armero (town 30km to west)
- The lahar engulfed and totally buried the town of Armero whilst people slept
- It killed 20,000 people in Armero alone
- Geologists knew the risks of the volcano and warned the authorities but they ignored their warnings
Hazards of volcanic tsunamis
Tsunamis are secondary effects of volcanism
- Volcanic edifices are inherently unstable, slope failure into water can generate large tsunamis. Long extinct volcanic islands can still pose major tsunami hazards eg. The subduction pacific plate under Japan is studded with seamounts
Eg. Anak Krakatau emerged from Sunda Strait in 1927
- On December 22nd, 2018, an eruption caused a landslide which resulted in a tsunami killing 437, with 14,059 injured
What happened at the Lake Nyos disaster?
- Lake Nyos is a crater lake in Cameroon, above a degassing volcano (very deep)
- Passive degassing of the volcano saturated the cooler water at the base of the lake with C02
- On the 21st august 1986, a landslide caused the water in the lake to mix. The C02 saturated water rose and degassed on to land. The dense C02 flowed along the ground, engulfing the nearby village of Nyos.
1,742 people and 6,000 cattle were suffocated
What happened at Mount St Helens?
On March 20th, small earthquakes detected under the volcano and on the 27th, the first outburst of ash and steam from the summit occurred.
- In April, tremors increased and magma was moving beneath the summit. There was swelling observed as the magma chamber filled.
- A large earthquake triggered the collapse of the north flank and this caused one of the largest ever recorded landslides
- The removal of mass, decompressed the magma chamber which triggered a sideways blast, then a vertical blast.
What are the long term impacts of volcanism?
There can be atmosphere and climate impacts
Eg. 1815 Mt Tambora erupted (Indonesia)
- It produced 175km3 of ash and pumice (VEI = 7)
- 10,000 people died by the eruption and tsunami
- >80,000 people died of starvation
It was one of the largest events humans have witnessed
What were the long term impacts of Mt Tambora (Indonesia) after the 1815 eruption?
The sky became hazy and was known as Turners atmospheric sunsets
- Temps dropped in the Northern hemisphere in 1816 as ash in the atmosphere blocked out sunlight, and was called ‘The year without summer’
- Crops failed and there were food shortages
- This climate event helped inspire Frankenstein by Mary Shelly (due to violent storms in summer)
What happened after the 1991 Mt Pinatubo eruption?
17 million tonnes of S02 erupted into the atmosphere (VEI = 6)
- 2 months after the eruption, volcanic Aerosols surrounded the earth
- The average global temperature fell to roughly 0.4 (evidence for global climate impact)
