Transcript WHAT IS SO BIG IT IS HARD TO FIND?

Introduction to “supervolcanoes”
• Watch the short clip about supervolcanoes.
• Take particular note of how they are created.
• http://www.youtube.com/watch?v=LWZSDi1T
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Distribution of supervolcanoes
Formation of a supervolcano at a hotspot
1) Number the statements on your sheet in the
correct order to explain how a supervolcano forms.
2) Split the explanation into three parts
a) Before the eruption
b) During the eruption
c) After the eruption
Extension: If you finish have a go at drawing some
……. ….diagrams to accompany the explanation.
Before an eruption…
• Magma rises up through cracks in the crust to
form a large magma basin below the surface.
• The pressure of the magma causes a circular
bulge on the surface several kilometres wide.
During an
eruption…
• The bulge eventually cracks, creating vents for lava
to escape through.
• The lava erupts out of the vents causing
earthquakes and sending up gigantic plumes of ash
and rock.
• As the magma basin empties, the bulge is no longer
supported so it collapses – spewing up more lava.
After an eruption…
• When the eruption is finished there’s a big
crater (called a caldera) left where the bulge
collapsed.
• Sometimes these get filled with water to form
a large lake (e.g. Lake Toba in Indonesia).
Characteristics of a supervolcano
TASK: Copy down the correct characteristics
• Emit at least 1000km3 of material
• Looks like a typical volcano with characteristic
cone shape
• Flat
• Cover a large area
• Erupt regularly
• Have a caldera (depression marking the collapsed
magma chamber)
Yellowstone
• Known to have
erupted 630,000,
1.3 million and 2
million years ago
• 1,000 times
bigger than Mt St
Helens eruption
• Popular with
tourists due to its
unique landscape
Another eruption at Yellowstone?
• There is evidence that the magma beneath
Yellowstone is shifting.
• The caldera is bulging up beneath Lake
Yellowstone.
• Signs of increasing activity in some geysers
(geothermal feature where water erupts into
the air under pressure).
• Ground has risen 70cm in some places.
• Scale:
• 450km N-S
• 600km wide
Effects of a supervolcano
Thousands of km3 of
rock, ash and lava
spewed out
Possible global
famine
Mini ice age
triggered
Thick cloud of super heated
gas and ash flow out at high
speed, killing, burning and
burying everything it touches
TASK: Which of
these do you think
are real? Why?
Why not?
Ash shoots out
kilometres into the
air blocking sunlight
over whole
continents
Ash settles over
hundreds of km2
Flooding
Extent of Yellowstone ash from last
eruption…
Effects of Yellowstone timeline
- Create a timeline in your exercise book.
- As you watch the video clip add predicted
impacts of the potential eruption to your timeline.
Immediate
• Everything in 100 mile radius incinerated
• Cloud of poisonous gases races across US – 30 mins to
cover Wyoming and cross into S. Dakota
• Evacuation impossible once cloud of ash has hit
• Ash 8ft deep and heavier than snow
• Ash clogs internal combustion engines and people are
stranded
• Emergency services unable to reach people
• People outside suffocated almost immediately by toxic gas
• Buildings collapse due to weight of ash
Within 1 week
• Ash would immobilise entire country
• 2/3rd USA covered by ash
• Ash washed into rivers turns to mud, blocks
channels and causes massive flooding in midwest
• Planes couldn’t fly and vehicles couldn’t drive
• Looting
• ‘dog eat dog’ post-apocalyptic situation
A few weeks later
• Temperatures plummet as gas and ash block
incoming sunlight
• Sulphuric gases & ash spread around world
Long term
• Mini ice age
• Global harvest failure  famine?
• Civilisation greatly changed
Your task
• Log on to this site – it is the story of Yellowstone.
• http://www.windowsintowonderland.org/hotspots
/high/index.html
• Read the story (I recommend switching off the
sound!) & add to your notes any key facts about
the tectonic aspects of the caldera.
• E.G, what is happening to the lake & why? What is
a hotspot, a fumarole, a geyser?