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 HelensMay 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

KrakatoaAugust 22, 1883

Largest volcanic eruption in recorded history (the last 5,000 years or so).

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.

There are no pictures of it…because it is literally gone.

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 evenMount Saint Helens…

Believe it or not…

It’s Yellowstone National Park

inWyoming.

Yellowstone is known as a SUPERVOLCANO.

What is a SUPERVOLCANO?(Exactly what the name

implies.)

When was the last supervolcano to erupt?

Toba 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.

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…