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 Pyroclastic Flow Lahars Caldera 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. Last eruption of any kind was 1944.

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. Eruption lasted 18-20 hours Pyroclastic flow followed Lava and ash flows buried people…suffocating them to death.

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.

1944 Eruption

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 Prior to 1991 last major eruption was 450 years ago Earthquake in July 1990 (very large) with epicenter about 50 miles from pinatubo started the events that lead to an eventual eruption. Two weeks after the EQ locals noticed steam starting to escape from Pinatubo March 15, 1991 many small EQ felt on the west side of the mountain. Lots of steam and ash were released over the course of a few days.

1991 Eruption 40,000 People were evacuated Series of 4 large eruptions 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 Everyone within 15 miles of the volcano was asked to leave…not everyone did People could see the dome get larger as the volcano got closer to eruption Ash in the air decreased the amount of sunlight reaching earth by 10% over the next 6 months. Last Eruption Lasted 9 hours At the same time a tropical storm (hurricane) was passing north of the region. This caused lots of rain and made a “muddy” ash-water mix that was about 13 inches thick and covered an area of about 10 miles surrounding the volcano. 100,000 + left homeless

Prior to eruption

Ash that blocked the sunlight caused the temp of earht to decrease by ½ a degree for about a year.

After eruption the volcano was about 200 feet shorter…lost in eruption.

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

Before and after the eruption

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 83 year old Harry Truman (not president) refused to evacuate…body never found.

Kilauea Active Volcano Shield 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 Active Most famous eruption in 1883 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 Caused earthquakes and tsunamis 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. Esplosions heard in australia