volcanoes
DESCRIPTION
Volcanoes. Lava. Lava: Molten rock outside the earth Magma: Molten rock inside the earth Types of Lava Aa Rough and Stone Like Looks like angular rocks Made of liquid lava and pieces of solid, cooled lava Pahoehoe Smooth surface Looks like one continuous flow of lava - PowerPoint PPT PresentationTRANSCRIPT
Volcanoes
Lava• Lava: Molten rock outside the earth• Magma: Molten rock inside the earth• Types of Lava
– Aa• Rough and Stone Like• Looks like angular rocks• Made of liquid lava and pieces of solid, cooled lava
– Pahoehoe• Smooth surface• Looks like one continuous flow of lava• Can resemble a rope
– Pillow• Formed when lava is cooled in water• Smooth and spherical
Volcano Terminology
• Tephra– A mix of gas, rock that are emitted from a volcano– Rock can be small (ash) or large (6 inches)
• Pyroclastic Flow– Tephra that flows along the ground quickly (450 mi/hr)
• Lahars– Mudflows made of dirt, tephra, and water. – Flow down the mountain often in riverbeds.
• Caldera– The crater left at the top of a mountain after an eruption.
What Volcanoes Look Like Underground
Vesuvius
• Only volcano on the European mainland.• First Eruption was 17,000 years ago.• Last major eruption was 100’s of years ago.– AD 79
• Composite Volcano• At a convergent Boundary between the
Eurasian and African plates.
AD 79 Eruption
• Buried the Roman towns of Pompeii and Herculaneum.
• 7 years prior to eruption there was a powerful earthquake that disturbed the volcano
• Small earthquakes became common leading up to the eruption.
• Erupted on August 24th – a day the Romans honored their god of fire.
AD 79 Eruption
• The site has been uncovered and studied• Most bodies were found in homes and
thought to have died of roof collapses.• Herculaneum was buried with 75 feet of ashes
and rocks. • Neither town was rebuilt after the explosion,
but new towns have grown and the mountain is again densely populated.
Pinatubo
• Active Volcano– Last major eruption was in 1991– First eruption was about 45,000 years ago
• Part of a chain of volcanoes in the Philippines• Many small eruptions since 1991• Composite Volcano• At a convergent boundary between two small
plates.
1991 Eruption
• The second largest volcanic eruption of the 20th century.
• Started with small eruptions and hundreds of small earthquakes daily.
• For two months steam and ash escaped the volcano.
• The escape for steam was blocked causing a buildup of pressure inside the volcano and an eventual eruption of lava on June 7th, 1991
1991 Eruption
• 40,000 People were evacuated– 800 people died
• Series of 4 large eruptions• Pyroclasitc flow and lahars followed• Ash covered everything within a hundred
miles– The roofs of about houses collapsed due to the
weight of the ash
Mt. St. Helens
• Last Major Eruption in 1980• First Erupted 40,000 years ago.• Largest Mt St Helens eruption of all time was
in 1480
1980 Eruption
• Started with an earthquake in March, steam started to be released, and then the side of the mountain started to bulge.
• Second earthquake in May caused the eruption to start.
• Lahars flowed down the many rivers in the area.• Plume of ash and steam reached Idaho in 3
hours.
1980 Eruption
• Explosion reduced the height of the mountain by 1300 feet.
• Damage was extensive– 57 people died– 7000 + big game animals died– 12 million fish in a nearby hatchery died– 200 homes damaged
• Whole area in now a national park
Kilauea
• Active Volcano– Continually erupting since 1983– Non-Explosive Eruptions
• Shield Volcano• One of 5 volcanoes on the Big Island in Hawaii– Hawaii Island
• Located at a “hot spot” not a plate boundary.– Thin area in the plate where magma can get through
the crust
Kilauea
• Erupted enough lava to pave a road around the earth 5 times.
• Destroyed multiple towns.• Creates fog when hot lava hits the ocean. • Lava explodes when it hits the ocean.• Native Hawaiians believe that it is the home of
Pele – the volcanic goddess.
Yellowstone
• Most of Yellowstone is located within a volcanic caldera.
• The volcano erupted 640,000 years ago.• There is evidence that it will erupt again, but
not in the near future.• HUGE!– Called a “super volcano”
• Located at a “hot spot” like Hawaii
Krakatoa
• In Indonesia– Between three separate islands.
• Active• Most famous eruption in 1883– Whole island destroyed– New island called Anak Krakatoa – “Child of
Krakatoa”• Small eruptions almost every year since.– April 2008 – Hot gas an lava were released
1883 Eruption
• Very violent explosions– Shockwaves were felt around the whole earth.
• Caused earthquakes and tsunamis• Killed 120,000 people total– Human skeletons found in Africa months afterwards.
• The temperature of the earth droped by 1.5 degrees for a whole year because of all the ash in the atmosphere.
