Chapter 6 Volcanoes

Volcanoes & Plate Tectonics Volcanic Activity

Volcanoes in Idaho??? http://www.youtube.com/watch?v=bgRnVhbfIKQ

Student Objectives• Students will discuss where volcanoes

generally form, specifically name the three types of locations, be able to draw picture showing how they form, and how it ties into plate tectonics.

• Students will distinguish between magma and lava and the three types of volcanoes.

• Students will also discuss how early volcanism changed the landscape of Idaho and describe its features.

Volcanoes

• The Eruption of a volcano is among the most dangerous and awe inspiring events on earth!

• A volcano is a weak spot in the crust where molten magma comes to the surface.

• Magma is a mixture of molten rock-forming substance that includes gases, and water vapor from the mantle.

• When magma reaches the surface, it is called lava

June 1991 Philippines Mt. Pinatubo

Mt. Vesuvius – The Unexpected!• On August 23, 79 AD, Pompeii looked like any

other busy, prosperous city. People were moving about, trading goods, news, and friendly talk.

• Three days later, on August 26, all of these sounds had fallen silent, and the place itself had vanished. Almost nothing was seen of Pompeii for more than 1500 years. Now, more than 1900 years later, we are learning more and more about the last days of Pompeii.

What happened to Pompeii preserved a treasury of information about life in the ancient Roman Empire.

The ash and lava quickly ended their lives and preserved their day’s activities.

These people below died instantly. Their bodies decayed inside the rock and ash tombs. Later, the

hollowed areas were filled in with minerals.

Other Famous Volcanoes

• 1883 Indonesia – Krakatau• 1902 Martinique – Mt. Pelee (29,000 killed)

• 1912 Alaska – Mt Katmai• 1991 Philippines – Mt Pinatubo• 1980 Washington – Mt St. Helens• Present - Kilauea - formed Caldera 1790• Japan – Mt Fuji – erupted 16 times since

781 ad, most recent in 1708

Location of VolcanoesThere are about 600 active volcanoes on land.

Many more lie beneath the sea.

Volcanoes occur in belts

that extend across

continents and oceans, such as

the Ring of Fire

in the Pacific Ocean.

Volcanic Destruction!

Several Different Locations of Volcanoes

Volcanoes can be found at • Convergent plate boundaries

• Divergent plate boundaries ● Hot spots

FIRST TYPE LOCATION

Volcanoes at Convergent

Plate Boundaries

Subduction causes slabs of ocean crust to be thrust down through a deep-ocean trench into the mantle. The crust melts and forms magma, which rises back toward the surface, erupting as lava.

SECOND TYPE LOCATION Volcanoes at

Diverging Plate

Boundaries• Volcanoes form along the mid-ocean ridge,

where new ocean crust is being formed and pushed in opposite directions.

• Only in a few places, such as Iceland and the Azores do the volcanoes of the mid-ocean ridge rise above the ocean’s surface.

Iceland is one the very few places where

the mid-oceanic ridge rises above

ocean’s surface.

This is a common

sight there!

THIRD TYPE LOCATION Hot Spot

Volcanoes

A hot spot is an area where magma from deep within the mantle melts through the crust like a blow torch. Hot spots often lie in the middle of continental or oceanic plates far from any plate boundaries.

Yellowstone marks a major hot spot. The last major eruption in Yellowstone was 75,000 years ago.

Volcanic Activity

• Just like CO2 trapped in a can of pop, the dissolved gases are under lots of pressure.

• A volcano erupts when an opening develops in weak rock on the surface. The gases dissolved in the magma rush out, carrying the magma with them in an explosive display.

8:30am May 18,1980 Mt St Helens

Mt St. Helens

• Movie: http://www.youtube.com/watch?v=vBJ9xZws7ro

This is the volcano named

after me! (after an episode a few

years ago where students didn’t study for

an important test!!!)

Late March, 1986

Mt. Augustine

Late March, 1986 Mt. Augustine

Volcanism in Idaho??? Yellowstone Snake River

The Snake River Plain extends 400 miles (650 km) westward from northwest Wyoming to the Idaho-Oregon border. The Snake River Plain is a broad, flat depression, which covers one quarter of the state of Idaho.

The heat is from a hot spot beneath Yellowstone that causes all the sensational features in Yellowstone.

This hot spot used to be under Idaho!!

The geysers, hot springs, and bubbling mud pots of Yellowstone National Park indicate there is extra heat beneath this corner of Wyoming.

Yellowstone's Rocky Mountain splendor Thousands of steaming geysers, shimmering

thermal pools, and bubbling mud pots are evidence of this hot spot activity

But the greatest wonder of all goes mostly unnoticed.

What’s going on in Yellowstone?Hidden underground, powerful volcanic, tectonic, and

hydrothermal forces are continually reshaping the landscape of Yellowstone.

Symptoms of the underground turmoil include numerous earthquakes (most too small to be felt), uplift and subsidence of the ground surface, and persistent but ever-changing hydrothermal activity.

Eventually, the unrest will culminate in another large earthquake or volcanic eruption, both of which have occurred many times before in Yellowstone's geologic past.

Calderas

The largest and most explosive volcanic eruptions eject tens to hundreds of cubic kilometers of magma onto the Earth's surface. When such a large volume of magma is removed from beneath a volcano, the ground subsides or collapses into the emptied space, to form a huge depression called a caldera. Some calderas are more than 25 kilometers in diameter and several kilometers deep.

Craters of the Moon is a volcanic field of old calderas. Craters of the Moon had 8 eruptive episodes from 15,000 to approximately 2,000 years ago.

Craters of the Moon lava field lies along the northern border of the Snake River Plain.

Eight times in the past 15,000 years lava poured from cracks which opened along this weak spot in the earth's crust.

Expanding gases in the lava ejected rocks hundreds of feet into the air.

The tops literally were blown off (and the ash landed in Nebraska and Wyoming) resulting in the Idaho smiley face.

– Beneath the crust of the Snake River Plain and into Yellowstone lies a "hot spot" or localized heat source.

– The hot spot does not move but rather remains in a fixed position.

– The crust of the earth moves over it; as the North American plate slides southwestward over the hot spot.

– As the plate moves over the hot spot volcanic eruptions occur on the surface.

This picture shows how the plate moves over the hot spot producing island arcs. Idaho’s caldera were formed in a similar manner!

Initially these eruptions were very violent.

Huge calderas of up to 30 miles in diameter were formed when these devastating eruptions took place.

Later a more fluid lava flowed onto the surface and covered the crater, giving it the smoother texture that we see in the satellite photos.

As you drive along the highway in southern Idaho, you are driving through these huge ancient Caldera!

Idaho’s Calderas

Calderas become progressively younger from west to east. The Yellowstone calderas are they youngest and mark the approximate location of the hotspot.

• http://www.youtube.com/watch?v=ESXWanLH7mU&feature=related

Video 4 minutes long:

Watch all the different kinds of lava flows

Notice how the houses instantly ignite when the lava comes close

Witness what happens to the highway when the lava creeps across

Why do you think the song may be appropriate for the name “Ring of Fire?”

Do you know the answer?

• Where do volcanoes generally form?

• What are the three types of locations?

• How do volcanoes ties into plate tectonics?

• What is the difference between magma and lava?

• What are the three types of volcanoes?

• How do we know that Idaho had ancient volcanoes?

• What kind of “volcano in the making” is found under Yellowstone National Park?

• A Volcanic Landscape The shallow arc of Idaho's Snake River Plain spans southern Idaho, gently rising from west to east. Current theories suggest that the plain marks the path of continental movement over a deep hotspot now lying beneath the Yellowstone Plateau. As the continent drifted southwestward over millions of years, calderas—super-volcanoes 10 - 40 miles (15 - 64 km) wide—erupted over the hotspot. When Yellowstone Caldera erupted 640,000 years ago, it released about 240 cubic miles (1,000 km3) of material, covering half of North America in 6 feet (2 m) of debris.

• In the past 17 million years, there have been about a dozen catastrophic eruptions releasing huge volumes of rhyolitic magma and ash. Between these super-eruptions were long periods when more fluid basaltic lava flowed from more than 8,000 shield volcanoes and numerous lava cones. Remnants of these dot the Eastern Snake River Plain today. Layer upon layer of basalt flows extend 3,000 - 6,000 feet (1,000 - 2,000 m) below the surface, completely covering the rhyolite "basement."

• 1. Sinking Rivers and a Flowing Aquifer Streams that flow here are indirect tributaries to the Snake River. The aptly named Lost River flows to an area known as "the sinks" where it soaks into the ground, becoming part of an aquifer the volume of Lake Erie. The aquifer flows through pores and fractures in the rock hundreds of feet beneath the surface, eventually emerging from springs along the Snake River Canyon at Thousand Springs about 100 miles (160 km) to the southwest.

• 2. Big Southern Butte Big Southern Butte, rising 2,500 feet (760 m) above the Eastern Snake River Plain, is a prominent reminder of the region's volcanism. About 300,000 years ago, the butte intruded through surrounding layers of basalt, rising to an elevation of 7,560 feet (2,300 m). It is one of the largest composite rhyolite domes in the world.