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Volcanism on the Earth
Questions.
 What is volcanism (volcanic activity)?
 Where does volcanic activity occur?
 Some interesting or important volcanoes.
Volcanic activity could be described as any place where material
from within the Earth reaches the surface.
Not all are explosive mountains. Some places are slow and
steady flow of material.
Probably the most common volcanism on Earth
we rarely see – it’s underwater at mid-ocean ridges!
Lava is not the only material to be ejected or released from
volcanic activity. What else might?
 Lava
 Ash
 Gases
 Pumice
 Steam
What is the difference between lava and magma?
Some volcanoes eject enormous amounts of
material.
Where does volcanic activity occur?
 Plate Boundaries
(usually)
 Convergent
 Divergent
 Transform
 Which ones have volcanic activity?
Convergent Boundaries
 Continental-continental? (Not usually.)
 Oceanic-oceanic? (Oh yeah. Subduction Zones!
Volcanic island chains formed.)
 Oceanic-continental? (You bet. Subduction
zones again! Volcanic mountains formed.)
Subduction zones are where we find typical volcanic
mountains, either on land or in the oceans.
Divergent Boundaries
 Mid-ocean Ridges
 Rift Valleys (like in Africa)
Mid-ocean ridges are divergent boundaries
but can also be places of volcanic activity.
Notice the volcanoes in the African Rift Valley,
also a divergent boundary
What about volcanoes that are not near plate boundaries,
like the Hawaiian Islands?
These are called “hotspots”.
Hotspots, like Hawaii. are places where heat from deep
within the Earth can penetrate through a plate.
Hotspots are believed to originate from very deep within
the earth, from the core itself.
Because the Pacific plate is slowly moving over the hotspot, the row of islands
represent the formation of them over many millions of years. So which island is
the youngest and which is the oldest?
There have been many hotspots identified on the Earth. A few
are actually on plate boundaries, but they can occur anywhere.
Some important or otherwise
interesting volcanoes.
Mount Saint Helens
May 18, 1980
 Washington State, USA.
 Largest volcano in North America in
modern times.
 57 people killed in spite of months of
warnings.
 How do volcanologists know when a
volcano might be ready to erupt?
 Click for video 3:33
 Largest volcanic eruption in recorded
history (the last 5,000 years or so).
Krakatoa
August 22, 1883
 Loudest sound recorded history.
 Sound reverberated around the world for
seven days.
 Over 6000 people killed.
 Most died from the incredible tsunami it
created (100’).
 Made water slosh as far away as the
English Channel.
Even bigger?
If the amount of stuff ejected from Mt. Saint Helens
was the size of a pea, then the stuff ejected from
Krakatoa would be the size of a golf ball.
For this next volcano, the last time it erupted the
amount of stuff would have been equal to a ball with
a six foot diameter…
So where is the LARGEST,
MOST DANGEROUS
active volcano known in the world today?
It’s closer to us than even
Mount Saint Helens…
Believe it or not…
It’s Yellowstone National Park
in
Wyoming.
Yellowstone is known as a
SUPERVOLCANO.
What is a SUPERVOLCANO?
(Exactly what the name implies.)
When was the last supervolcano to
erupt?
 Toba is in Sumatra. This is what it
looks like today – the caldera is a
massive lake called Lake Toba.
 It was the last time a
supervolcano erupted on Earth,
and that was 74,000 years ago.
 This eruption brought humans to
the brink of extinction (only a few
thousand people on Earth
believed to survived).
 Caused at least six years of
“volcanic winter”.
 It was a whopper. A supervolcano
is practically inconceivable.
Toba
And Yellowstone is even more dangerous.
 The entire park is the crater
(caldera) – 1500 sq. miles, 40
miles across, 8 miles thick.
 A massive magma chamber
rests directly underneath the
park. It is one giant
HOTSPOT. (The only
hotspot found on land.)
 That explains the
spectacular geysers and hot
springs.
Yellowstone is a beautiful place, even if it is the world’s
most dangerous volcano.
What might be going on under the park?
History of eruptions.

Last eruption was 640,000 years
ago.

(It was 1000x bigger than Mount Saint Helens.)

The one before that was 1.3 million
years ago.

(It was 280x bigger than MSH.)

The one before that was 2.1 million
years ago.

(That one was 2500-8000X bigger than MSH,
which is unbelievable.)
Yellowstone has erupted at least 100 times in
the last 16.5 million years.
When will be the next one?
Any time.
Yellowstone erupts, on average, every
600,000 years. The last eruption was 640,000
years ago.
It appears that Yellowstone is overdue...
(Click for video 1:25)
I don’t think anybody wants to be around when the next
supervolcano erupts…