Volcanic Hazards. Volcanoes. part 2

Volcanic Hazards Volcanoes part 2

Lava flows

Lava flows can usually be avoided by people. Often it is property that is damaged or destroyed

Remains of San Juan Parangaricutiro, Mexico

Aa flow moving over pahoehoe

Blocky basalt flow in Lassen NP This lava flow came from the base of a cinder cone.

Fissure Eruption Fissures are usually found in or along rifts and rift zones, such as Iceland and the Great Rift Valley in Africa, but examples can also be seen in Hawaii.

In 1973 a fissure eruption surprised the Icelandic island of Heimaey. The eruption began without warning just outside the town of Heimaey.

Townsfolk successfully used water to save the habor from being closed by lava flows, but around 400 homes were lost.

Ol Doinyo Lengai, Tanzania cool (500 deg. C) carbonate lava---very unusual

Gas easily escapes from low viscosity lava and escaping gas often propels lava into the air.

Explosive Eruptions Lava Dome Lava spine Mount Pele 1902 1993 Plinian eruption of Lascar volcano, Chile

Pelean Volcanic Hawaiian Plinian Strombolian Vulcanian Explosivity Index and Eruption Type Classifications

1991 Mount Pinatubo, Philippines

Volcanic Explosivity Index (VEI) Noticeable global atmospheric effects from dust. Average global temperature dropped about 0.4 C but many pretty sunsets observed. Global temperature dropped known as the year without a summer. Tens of thousands died from famine. This volcano caused the worst famine of the 19th century.

Mount Fuji, Japan

Mount Saint Helens (pre 1980)

Mount Saint Helens 1980

Mount Saint Helens is a stratovolcano with a lava dome growing in it s crater.

Mount St. Helens Lateral/Directed Blast

Pyroclastic Surge, Pyroclastic Flows and Lateral Blasts, Are extremely powerful and dangerous events. They can scour and scorch the surface of some areas and bury other areas under thick deposits of rock and ash.

Collapse of eruption column

A lethal pyroclastic flow and surge in progress at Mt. Merapi, Indonesia. 2009

Pyroclastic Flow Deposit

Pyroclastic Flow Disasters St. Pierre 1902 30,000 killed by Mount Pelee Mount Vesuvius wipes out Pompei, and Herculaneum

Pyroclastic flows descend the south-eastern flank of Mayon Volcano, Philippines. Maximum height of the eruption column was 15 km above sea level, and volcanic ash fell within about 50 km toward the west. There were no casualties from the 1984 eruption because more than 73,000 people evacuated the danger zones as recommended by scientists of the Philippine Institute of Volcanology and Seismology.

Tephra (Volcanic projectiles and ash)

Anak Krakatau in a vulcanian eruption, 23. November 2007. Note bombs or blocks near the ash plume. Photo Marco Fulle.

Volcanic Bombs and Blocks Volcanic bombs can be thrown many km s from an erupting vent, and often acquire aerodynamic shapes during their flight. The 1935 eruption of Mount Asama in Japan expelled bombs measuring 5-6 m in diameter up to 600 m from the vent.

Lapilli "little stones"

Volcanic Ash

Ash bed in San Francisco from Mt. Tehama (proto-mt. Lassen) over 200 miles away

Philippines 1991

Pinatubo Ash erosion---lahars from these ash deposits have killed many.

Lahars Mudflow/debris flow formed from volcanic materials. Lahars can be triggered by an erupting volcano melting snow and ice. Lahars can also form from wet weather mobilizing ash deposits after eruption activity has ceased. Lahars can have the consistency of wet cement.

Lahars are a major threat in volcanic regions. Tens of thousands of people have been killed by lahars. The town Armero was located in the middle of the photo. Over 20,000 people were killed by lahars from the volcano Nevado del Ruiz which was 30 miles away.

This view is along the Muddy River, southeast of Mount St. Helens.

Lahar deposit from Mount Pinatubo

Lahar deposits in Plymouth, Montserrat

Mazuku is a pocket of oxygen-poor air that can be lethal to any human or animal life inside. The term comes from Swahili and means "evil wind."

Volcanic Gases

Volcanic gases Volcanic gases were directly responsible for approximately 3% of all volcano-related deaths of humans between 1900 and 1986. Some volcanic gases kill by acidic corrosion; others kill by asphyxiation. water vapor (H2O), carbon dioxide (CO2), sulfur either as sulfur dioxide (SO2) (high-temperature volcanic gases) or hydrogen sulfide (H2S) (low-temperature volcanic gases), nitrogen, argon, helium, neon, methane, carbon monoxide and hydrogen. Some volcanic gases including sulfur dioxide, hydrogen chloride, hydrogen sulfide hydrogen fluoride react with other atmospheric particles to form aerosols.

3 MAIN GASES: CO 2 (carbon dioxide) H 2 O (water) SO 2 (sulfur dioxide)

Horseshoe Lake tree kill near Mammoth in Long Valley Caldera Carbon dioxide poisoning caused the deaths of 3 ski patrolman who fell into a low spot.

Volcanic Landslides and debris avalanches Hydrothermally altered areas can be areas of weakness and can fail. Lava domes can build up until unstable slope are developed. Lava dome frequently have large spines surface. These spines can be unstable. Volcanoes can bulge from internal pressure and become unstable. Fissures can develop on the flanks of some large volcanoes suggesting possible structural collapse. Hawaiian lava flows that flow into the ocean are quenched and create unstable benches that often eventually collapse. The collapses can be explosive when a large volume of lava suddenly enters the ocean.

Volcano related tsunami Flank collapse on Hawaii is thought to present a danger for creating a megatsunami in the Pacific Ocean. There is evidence that this has occurred in the past. The western half of the Cumbre Vieja in the Canary Islands has developed fissures and presents a danger of collapsing into the Atlantic Ocean. If this 500 cubic Km mass of land catastrophically collapses it could generate massive wave that could devastate the east coast of the U.S. and the Caribbean. Krakatoa eruption generated a devastating tsunami. The island exploded in 1883, killing approximately 40,000 people--most deaths are due to the tsunami waves. The explosion is still considered to be the loudest sound ever heard in modern history, with reports of it being heard nearly 3000 miles from its point of origin. The shock wave from the explosion was recorded on barographs around the globe.

What type of volcano is this?

Crater Lake, OR

Caldera Examples: Long Valley, Yellowstone, Aso, Crater Lake, Toba, La Cumbre.

Long Valley Caldera Eastern California

Nevada Mono Lake Long Valley Caldera Death Valley 20 mi

Maar Ground water explosively flashes to steam when magma comes in contact (Phreatic eruption). Examples: Ubehebe Crater, Zuni Salt Lake

Viti maar at Askja, Iceland; Öskjuvatn caldera in background. Note person (P. Alean) on crater rim. Photo: J. Alean

Little Ubehebe Ubehebe Crater (maar) in Death Valley

Asosan is the largest active volcano in Japan, and is among the largest in the world. One of the largest caldera in the world Aso Caldera, Kyushu Japan

A cinder cone in Aso caldera

Naka-dake volcano in Aso

Lateral Blasts/landslide

Hazard Definition Speed Distance travelled Dangers Dust, ash, and pyroclastic bombs Material thrown from the vent of a volcano Ash: as fast as wind (20-80 km/h) Ash: All over world, potentially Ash: Roof collapse, Asphyxiation, clogged machinery, lost crops, breathing problems increased for asthmatics, Bombs: bodily injury or death Lahar Mudflow: ash + water (rain or melted glacier) Pyroclastic flows Lava flows Gas clouds Acid rain Ash, gas, lava, rocks Flowing molten rock High density rolling CO2 gas. SO2 gas + H2O creates sulfuric acid. Up to 40-50 km/h Up to 200 km/h 100s of km from vent (along river valleys) 10s of km from vent 2-4 km/h 10s of km from vent (if basalt), 1 km if rhyolite?? 10s of km from vent Same as wind 10s of km from vent Drowning, destruction of all bridges and buildings near water s edge Death and destruction to any and all in its path. Destruction to property and vegetation. Little hazard to human life. Asphyxiation of all life. Temporary lull in growth of vegetation and contamination of water.

What type of volcano is this? Volcano Skjaldbreiður, National Park of Þingvellir, Iceland.

Mauna Kea

Arenal Volcano Costa Rica

Mount Rinjani eruption in 1994, in Lombok, Indonesia