lecture 3 volcanic hazards

Question 1

What is an extinct volcano

Answer 1

A volcano with no chance of ever erupting again

Question 2

What is a dormant volcano

Answer 2

Have not erupted in the last 10,000 years but still have the potential to erupt

Question 3

what are Active volcanoes

Answer 3

have erupted in the last 10,000 years and still have the potential to erupt.
- 15000 active volcanoes
- 60 eruptions per year
- 20 eruptions at any given time

Question 4

What is the physical threat posed by a volcano

Answer 4

• type of volcano
• crater lake or ice/snow cap presence
• pyroclastic flow hazard
• Lahar Hazard
• lava flow hazard
• eruption frequency
• maximum VEI

Question 5

What are the primary hazards of volcanoes

Answer 5

• Lava flows
• pyroclastic flows/surges
• Tephra and ballistic projectiles
• gas emissions
• Debris avalanches
• earthquakes

Question 6

Describe a Lava flow

Answer 6

• Primary hazard
• Temperatures 880-1200 degrees Celsius
• when temperatures are below 800oC a skin forms on the surface.
• lava flows advance slowly so people can escape
• cause more damage to ground - destroys everything in its path/ destroyed by fire.

Question 7

What are Hawaii’s - Kilauea lower east rift zone eruption, 2018 impacts

Answer 7

• 24 injuries
• 700 houses destroyed
• $800 million damage

Question 8

Describe pyroclastic flows

Answer 8

A flow of hot gas and volcanic material
- from vesiculated, low-density pumice to vesiculated dense clasts.
- contains 10% of solid by volume
- tends to follow topographic lows (valleys).
- speed >10m/s to 300 m/s
- temperature 100-1100 degrees Celsius
- distance travelled: kilometres to 10s of kilometres.

Question 9

explain what a Pyroclastic surge

Answer 9

Pyroclastic surge:
a turbulent, low-density, high-velocity
part of a pyroclastic flow. Not constrained by topography;
contains 0.1-1% of solids by volume (i.e. higher gas to rock ratio).

Question 10

What’s the difference between a pyroclastic flow and a surge?

Answer 10

FLOW
- higher density
- travel closer to the ground
- laminar flow

SURGE
- lower density
- turbulent flow

Question 11

name the case study example for pyroclastic flow

Answer 11

Mount Merapi 2010

Question 12

What knock on effects do pyroclastic flows cause?

Answer 12

Health hazards (injury and loss of life, respiratory and eye)
- Destruction by direct impact (buildings, vegetation etc. )
- burying sites with hot rock debris (up tp 200m) which can result in mudflows (lahars) and landslides etc.
- destruction by fire
- malfunction of machinery (including aeroplane engines )
- increase surface water acidity
- climatic effects (reduces T; increased rainfall)

Question 13

explain the primary impact of gas emissions

Answer 13

examples of gases:
- sulphur dioxide (SO2)
- carbon dioxide (CO2)
- Hydrogen fluoride (HF)
these pose the greatest hazard potential (from gases) to people animals, agriculture and property.

Question 14

explain SO2 in the context of a volcanic gas

Answer 14

SO2
: air pollution, acid rain, climatic effect
(emission rates between <20 to 10 million
tons/day)

Question 15

explain co2 in the context of volcanic gas

Answer 15

CO2
: at concentrated levels lethal to
people and animals (average volcanic
emission rate of 130 million tons/year)

Question 16

explain HF in the context of volcanic gas

Answer 16

HF: can cause death and injury in livestock
during ash eruptions if fluorine content on
e.g. grass exceeds 250 ppm (destroying
bones of animals)

Question 17

What are the impacts of gas emissions from Lake Nyos

Answer 17

• 3000 cattle dead in the fields – Even ants were dead in their tracks
• Absolutely no sign of – injury or burns on bodies – unusual odors – damage to structures
• 1700 people in 6 different villages
  killed – Along with every other living creature in area
• Traced path of death 16 km up to the lake.

Question 18

What caused the problems at lake nyos

Answer 18

Small landslide into the lake
* Caused overturn - rapid degassing of
accumulated magmatic CO2
* Released ~ 1.3 x109 m3 of CO2
formed a cloud of CO2 50 meters thick
* Being heavier than air - moved down slope
* Lake level fell 1 meter.

Question 19

Earthquakes and volcanoes relationship

Answer 19

Earthquakes associated with volcanic eruption:
* rarely >mag. 5 on Richter Scale
* often trigger eruptions or generate landslides that can result in eruptions
Patterns that become progressively shallower are symptomatic of moving magma

Question 20

What are the secondary/ indirect volcanic hazards?

Answer 20

• Lahars (mudflows)
• Flooding / tsunami
• Fires
• Air pollution
• Diseases / famine
• Social effects
• Climatic effects

Question 21

What causes a mudflow or lahar?

Answer 21

Typically produced in response to pyroclastic flows interacting with severe rain, river water, crater lakes or volcanic glaciers
Especially associated with pyroclastic eruptions, characteristic of subduction zone settings

• The initial gas-rich pyroclastic flow is converted to a fast
  moving heated mud-flow. These flows generally follow river valleys and other topographic lows.
• Speed up to 200 km/h, temperature <100°C
• Distance travelled between kilometres to 10s of
  kilometres

Question 22

explain lahars due to glacial bursts

Answer 22

Melting of glaciers or snowfields by hot lava, ash or gases can result in highly fluidized hot mud flows.
* Such glacier bursts are associated with high altitude volcanoes and those at high latitudes.
* Example: Nevado del ruiz, colombia

Question 23

what are the impacts of lahars?

Answer 23

• destroy directly
• block tributary streams
• increased deposition of sediments
• bury communities

Question 24

Eyjafjallajokull eruption, Iceland April 2010

Answer 24

Eyjafjallajökull eruption, Iceland April 2010
* Seismic activity (1000s small eathquakes, 1-2 Mw, 7-10 km beneath volcano) commenced in December 2009 and led to a fissure eruption on 20 March 2010
* The eruption on 14 April 2010 resulted in ~110 million cubic meters of ejected tephra during explosive eruption, and the plume rose to ~9 km into the atmosphere..
The eruption penetrated the icecap
(April 17th 2010); note ash covering
the glacier.
Ash from 14 April eruption led to widespread disruption of air travel from
15 April, with much of the airspace in Europe closed until 20 April.
* About 500 farmers and their families from the
areas of Fljótshlíð, Eyjafjöll, and Landeyjar
were evacuated
* The thick layer of ash that fell on farms and
pastures (at Raufarfell) became wet and
compact, making it very difficult to continue
farming, harvesting or grazing livestock
Main eruption triggered meltwater floods that rushed

Question 25

explain, Tsunami – Hunga Ha’apai underwater volcano eruption 15 January, 2022

Answer 25

Hunga Ha’apai, is part of the Tonga-Kermadec volcanic arc, and rises 2,000 m from sea floor.
* Unusual high eruption plume -> 30 km into the upper atmosphere
* Combination of underwater eruption (water magma interaction) and high eruption plume -> new eruption style?
* Eruption triggered pressure and gravity waves in the atmosphere and tsunami waves all around the Pacific Ocean.
* Combined effect of tsunami and extensive ash fall
* ~US$90.4M damage
* ~600 buildings (300 residential ones) destroyed -> US$43.7M
* 85% of Tonga’s agricultural households affected by crop lost, damage to reef fisheries -> US$20.9M damage
* Infrastructure damage (roads, causeways, power supply, submarine cables etc.) -> US$20.9M
* Ash clean-up cost ~US$

Question 26

what are the climatic effects of volcanoes

Answer 26

Ash in upper atmosphere reduces amount of radiation reaching the ground.
(Krakatoa reduced T worldwide by 0.5 oC for
10 years).
Some speculation that chlorine flux from
volcanoes must be considered with CFCs as a potential contributor to stratospheric ozone
depletion

Question 27

Key questions

Answer 27

Key Questions
* What are the main direct hazards of volcanic eruptions?
* What are the main indirect hazards of volcanic eruptions?
* What type of volcanism produces pyroclastic flows?
* What are lahars and how do they form