Volcanoes Lava Lava Molten rock outside the earth

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

Aa

Pahoehoe

Pillow

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 24 th – 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 20 th 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 7 th, 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.