Volcanoes

Volcanoes11.1

What Causes Volcanoes?

I. Volcanoes and YouA. Volcano – opening in Earth’s surfaceB. Often forms a mountain from layers of lava

and volcanic ashC. Most are dormant, not currently activeD. More than 600 currently activeE. Mount St. Helens

a. http://volcanoes.usgs.gov/volcanoes/st_helens/st_helens_geo_hist_102.html

b. http://www.history.com/videos/mount-st-helens-erupts

c. http://volcanoes.usgs.gov/volcanoes/st_helens/st_helens_geo_hist_100.html

F. Active Volcanoesa. Kilaua volcano in Hawaiib. www.cbsnews.com/video/watch/?id=50133863nc. www.youtube.com/watch?v=GX0yPGCEtLkd. Iceland known for active volcanoese. http://www.cbsnews.com/video/watch/?id=63390

52nG. Eruptions of the Century

a. Mount Katmai, June 6, 1912 on the Alaska Peninsulai. 30 times greater volume than Mount St. Helens

b. Mount Pinatubo, June 1991, Philippinesi. Killed nearly 900 peopleii. Millions of tons of sulfur dioxide and ash into

Earth’s upper atmospherec. Mount Unzen, June 1991, Japan

i. 44 people died

II. How do Volcanoes Form?A. Heat and pressure cause rock to melt and

form magma.B. Magma Forced Upward

a. Magma is less dense than rock, so it is pressed upward.

b. Vent – opening through which magma flows out

c. As lava flows out, it cools quickly and becomes sold, forming layers of igneous rock

d. Crater – steep-walled depression around a volcano’s vent

III. Where do Volcanoes Occur?A. Volcanoes are directly related to Plate

movement and hot spots.B. Plates Moving Apart

a. Iceland has volcanic activity because it sits on top of the Mid-Atlantic Ridge.

b. Mid-Atlantic Ridge – plates moving apart forming rifts

c. Magma flows from rifts and is cooled by seawater

d. As more lava flows, it builds upe. It can form islands such as Iceland

C. Plates Moving Togethera. Soufriere Hills volcano on the island of

Montserratb. Formed because North American and South

American Plates are being forced under the less dense Caribbean plate

c. Magma forms because the forced under plates get hot enough to partially melt

d. Magma is forced up forming the volcanoes of the Lesser Antilles

D. Hot Spotsa. Hawaii, not at a plate boundaryb. Some areas of mantle are hotter than othersc. Hypothesis is that hot spot magma forms at

the boundary between the mantle and the outer core

d. Magma rises carrying heat from Earth’s core

e. Hawaii formed when volcanoes rise above the water.

f. Islands in a straight line because plate is moving over the stationary hot spot.

g. Kauai is the oldest island.

h. As plate move, Kauai moved away from hot spot and became dormant.

i. Islands formed over about 5 million years.

Chapter 11Types of Volcanoes

11.2

I. Styles of EruptionA. Trapped Gases

a. Water vapor and carbon dioxide are trapped in magma by the pressure of surrounding magma and rock

b. As magma nears surface, there is less pressure.

c. Gas escapes easily during quiet eruptionsd. Gas that builds up to high pressures

eventually causes explosive eruptionsB. Magma Composition

a. Low in silica means fluid lava, and quiet eruptionsi. Kilaueaii. Lava pours from vents, down the sides of a

volcanoiii. Trapped gasses can escape easily

b. Silica-rich magma produces explosive eruptionsi. Sometimes forms where plates are moving

togetherii. Silica-rich magma is thick, and gases get

trappediii. When an explosive eruption occurs, gases

expand rapidly, often carrying pieces of lava in the explosion

C. Magma Water Contenta. High water content causes explosive eruptions

II. Forms of VolcanoesA. Depends on type of explosion and type of

lava

B. Shield Volcanoa. Quiet eruptionsb. Silica-poor lavac. Flat layersd. Shield Volcano –

broad volcano with gently sloping sides

e. Hawaiian Islands

C. Cinder Cone Volcanoa. Explosive

eruptionsb. Tephra – rock or

solidified lava dropped from the air

c. Varies in sized. Cinder Cone

Volcano – steep-sided volcano formed by loosely packed tephra

D. Composite Volcanoa. Varies in

explosionsb. Composite

Volcano (Stratovolcano)– volcano formed from cycle of lava and tephra

c. Mostly found where plates come together

d. Mount St. Helens

VolcanoesIgneous Rock Features

11.3

I. Intrusive FeaturesA. Igneous rock – rock formed from fast cooling

lava at or near Earth’s surface (extrusive igneous rock) and from slow-cooling magma deep inside Earth (intrusive igneous rock)

B. Batholithsa. Batholiths – largest intrusive igneous rock

bodiesb. Hundreds of kilometers wide and long, and

several kilometers thickc. Can be exposed by erosiond. Granite domes of Yosemite National Park are

the remains of a huge batholith that stretches across much of the length of California

C. Dikes and Sillsa. Magma can squeeze into cracks in a rock

below the surfaceb. Dike – magma squeezed into a vertical crackc. Sill – magma squeezed into a horizontal crackd. Run a few meters to hundreds of meters long

II. Other FeaturesA. Volcanic Neck – solid igneous core left after

cone erodes awayB. Caldera – large opening made when the top

of a volcano collapses after an eruptionC. Igneous Features Exposed

a. Process of erosion wear down rock at the surface exposing features like batholiths, dikes, and sills.