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VolcanoesFormation, Risks and Opportunities
Volcanoes• Why do some places
have volcanoes and not others?
• Are all volcanoes the same? What are the
differences?• Are all volcanoes deadly?• Despite the risks, why do
so many people chose to live near to volcanoes?
Definition:
A conical mountain or hill, having a crater through which lava, rock fragments, hot vapor, and gas erupts.
Three volcanoes of southern Chile from the air: Villarrica (prominent peak in the foreground), Quetrupillan (snow-covered region in the middle ground) and Lanin (snow capped peak in the distance).
Japan Self-Defense Force soldiers and firefighters work among mountain lodges covered with volcanic ash near the peak of Mount Ontake on September 28, 2014.
An undersea volcano is seen erupting off the
coast of Tonga, March 18, 2009
The Aleutian Islands are a chain of 14 large volcanic islands and 55 smaller ones belonging to both the United States and Russia.
The Aleutian Islands, aerial view
Describe the distribution of volcanoes around the world
Why so many?• Majority of the plate
boundaries here are CONVERGENT boundaries.
• COMPRESSIONAL and DESTRUCTIVE nature of the plate movements here
• = more fractures found along the crust
• + the crust here is more BRITTLE (see explanation next slide)
SubductionOceanic Continental
When one oceanic plate meets another, the denser plate is forced downward into a deep ocean trench.
This plate, as it is subducted, releases water into the base of the over-riding plate, and this water mixes with the rock, thus changing its composition causing some rock to melt and rise.
Indonesia has the most volcanoes in any one country. 127 active and 23 inactive.
Refer to Fig. 1.38, p.26
Refer to p.27 to 28• Compare and contrast Figure 1.41 and Figure 1.43• Slope/gradient?• Materials?• Eruption intensity?• Openings?• Example?
Shield VolcanoMauna Loa Volcano, Hawaii
Less violent eruption
Gently sloping
Broad base
Formed by lava low in viscosity= Lava spreads over a large area= Lava cools and solidifies slowly
Hawaiian Eruption
Steep slopes at the top
Formed by lava high in viscosity= Lava spreads over a small area before solidifying
Gentle slopes towards the bottom
CONCAVE PROFILE
Composite VolcanoMt Rainier, Washington
Erupts violently• Pyroclastic flows• Lahars / mudflows• Huge ash clouds• Lava flows
Aniakchak Caldera, Alaska, United States
Formation of a Caldera1
2
3
4
5
See: https://www.youtube.com/watch?v=gQRt2NCmEw8
Mount Katmai, Alaska, United States
What about hotspots?
Hotspot Volcanoes
Hotspot at Hawaii
Places known as hotspots or hot spots are volcanic regions thought to be fed by
underlying mantle that is anomalously hot compared with the surrounding mantle.
They may be on, near to, or far from tectonic plate boundaries.
Difference betweendivergent plate boundary?
• The magma plumes found at a hotspot stay ‘fixed’ and do not move, regardless of the movement of the plates.
• The magma plume found at a divergent plate boundary is tied to the movement of the plates and moves along side it.
Divergent Boundary
Hotspot
Despite the risks…Why do millions of people continue to live near volcanoes?
Living with Volcanoes (p.39-42)Risks Benefits Destruction and death
by: Volcanic materials Landslides
Disruption of way of life
E.g. air planes grounded for days/weeks
Villages wiped
Fertile soils Minerals and
precious stones Tourism Geothermal energy
2010 Eruptions of
Mount Merapi
353 people were killed during the eruptions, many as a result of pyroclastic flows.
Rescuers search for victims of the Mount Merapi eruption
Yet despite the risks…
Others: Tourists at Kilauea on the Big Island of Hawaii
Others: Volcanic diamonds – not just jewellery!
The applications for diamonds are diverse and plenty
Others: Geothermal plants in Iceland
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