A mountain that forms when magma reaches the surface.
Under certain conditions, small amounts of mantle rock can melt, forming liquid magma. The magma rises upward through the crust, erupting at the surface as a volcano.
Magma rises because it is less dense than the solid rock around and above it.
Structure of a Volcano
Before an eruption magma often collects in a pocket called a magma chamber.
Magma rises to the surface in a narrow, vertical channel – pipe.
Vent- opening in ground where magma escapes to surface.
Crater- top of the central vent in most volcanoes is a bowl-shaped pit.
Caldera- chamber and main vent when empty may fall in creating a huge depression.
Location of Volcanoes
Most occur along plate boundaries or at hot spots in the crust.
Hot Spot- region where hot rock extends from deep within the mantle to the surface.
3 major types of Volcanoes
Shield volcanoes- quiet eruption of low-viscosity lava and produces a wide, flat volcano.
Cinder cones- Eruption that is entirely ash and cinders and results in a small, steep-sided volcano.
Composite volcanoes- Explosive eruptions that produce a combination of lava and ash.
How a Volcano Erupts
Magma is under pressure and contains dissolved gases (Carbon dioxide and water vapor).
As magma approaches the surface, lower pressure allows the gases in magma to expand rapidly.
Eruption occurs when the gases bubble out through a crack in the crust.
Quiet and Explosive Eruptions Quiet- very hot, low-silica magma
generally erupt quietly. Lava erupts in a stream of low-viscosity
lava called a lava flow.
Explosive- high-silica magma. Thick magma can clog a volcanic pipe causing enormous pressure to build up.Trapped steam inside the volcano adds to the pressure.
- Lava solidifies quickly
Significant Eruptions and Environmental Impacts Mount St. Helens (1980)- Washington State, killed
57 people and large numbers of wild animals. Large areas of forests were obliterated. Through succession some vegetation has returned.
A positive from volcanoes is highly fertile soils from weathering of lava.
Tambora 1815- Indonesia, largest in recorded history. 71,000 people died from impact alone or starvation and disease afterwards. Ruined agriculture and livestock- lead to worst famine in 19th century.
Krakato 1883- Indonesia. Produced tsunami with waves reaching 120-140 ft. 40,000 people killed. Loudest explosion- heard 3000 miles from origin.
Mt. Vesuvius 1979- Italy. Wipes out entire town. Hundreds of years later everything and everyone was found by archaeologists, perfectly preserved in ash. 13,000 people died.
Yellowstone-super volcano. Researchers report the super-volcano
underneath the state of Wyoming has been rising at a record rate since 2004. Its floor has gone up three inches per year for the last three years indicating the fastest rate since records began in 1923
Movement of Earth’s lithosphere that occurs when rocks in the lithosphere suddenly shift, releasing stored energy.
Small portion of this energy is carried by vibrations called seismic waves.
Stress in Earth’s Crust
Stress- force that squeezes rocks together, stretches or pulls them apart, or pushes them in different directions.
As tectonic plates move, they cause stress in the crust, which in turn produces faults and folds.
Fault- break in a mass of rock along which movement occurs
Fold- bend in layers of rock
Faults and Folds
San Andreas Fault Earthquake Fold in California
Earthquakes and Seismic Waves Earthquakes occur because stress forces
have exceeded the strength of rock. The location beneath Earth where an
earthquake begins is called the focus. Epicenter- location on Earth’s surface
directly above the focus. As earthquake occurs, seismic waves
move out in all directions from the focus.
Types of Seismic Waves
Longitudinal waves similar to sound waves.
Compress and expand the ground like an accordion. Particles move in direction of waves.
Fastest seismic waves and first to be detected at a distance.
Travel in solids and liquids.
Transverse Waves like light.
Particles move at right angles to the direction of the waves.
Cannot travel through liquids.
P Waves- Primary Waves S Waves- Secondary Waves
P and S Waves
Waves that develop when seismic waves reach Earth’s surface.
Move more slowly than P waves and S waves, but usually produce larger ground movements and greater damage.
Some are transverse waves and others have a rolling motion similar to ocean waves.
Seismograph- record seismic waves to measure and pinpoint their epicenters.
Richter Scale- rates earthquakes based on measurements of the times and amplitudes of seismic waves by certain seismographs.
Moment Magnitude Scale- most useful, gives a measure of the amount of energy released.
Modified Mercalli Scale- ranges from 1-12 and is based on observations in the areas affected.
Significant Earthquakes and Environmental Impacts Permanent vertical or horizontal
displacement of the ground affects people, buildings, bridges, freeway overpasses, dams, pipelines.
China 1976- 655,000 deaths Haiti 2010- 316,000 deaths Peru 1970- caused massive landslide
that buried the town of Yungay killing 17,000 people.
Large sea wave generated by an underwater earthquake, volcano, or landslide.
Significant Tsunamis and Environmental Impacts March 11, 2011- Japan, earthquake that
led to a tsunami. Dead/missing is 22,000. Radioactive material released into atmosphere.
2004 Indian ocean earthquake that led to tsunami. The earthquake was the result of the sliding of the portion of the Earth's crust known as the India plate under the section called the Burma plate. 228, 000 people died. Devastated many coastal areas.
Intact mangrove forests helped protect buildings and people.
In Sri Lanka, greatest damage occurred where illegal coral mining and reef damage had caused severe beach erosion.
Areas affected by 2004 tsunami
Asia Tsunami Timeline
1. The hypothesis that the continents move slowly over Earth’s surface is called?
2. New ocean crust is formed along?3. What is a break in a rock mass along
which movement occurs?4. The location where earthquake begins?5. Cause Earth to vibrate in the direction of