Презентация на тему: Volcanic Eruptions and Hazards

A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth’s crust to the Earth's surface. A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth’s crust to the Earth's surface. The volcano includes the surrounding cone of erupted material.

Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface. Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface. Same principle as hot air rising, e.g. how a hot air balloon works When magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it as to how it erupts. Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption! Think about shaking a carbonated drink and then releasing the cap. Small amounts of gas and (or) low viscosity (runny) magma will form an effusive eruption Where the magma just trickles out of the volcano (lava flow).

Explosive volcanic eruptions can be catastrophic Explosive volcanic eruptions can be catastrophic Erupt 10’s-1000’s km3 of magma Send ash clouds >25 km into the stratosphere Have severe environmental and climatic effects Hazardous!!!

Three products from an explosive eruption Three products from an explosive eruption Ash fall Pyroclastic flow Pyroclastic surge

Effusive eruptions are characterised by outpourings of lava on to the ground. Effusive eruptions are characterised by outpourings of lava on to the ground.

92,000 Tambora, Indonesia 1815 92,000 Tambora, Indonesia 1815 36,000 Krakatau, Indonesia 1883 29,000 Mt Pelee, Martinique 1902 15,000 Mt Unzen, Japan 1792

Pyroclastic flow Pyroclastic flow Lahars/Mud flows Pyroclastic fall Lava flow Noxious Gas Earthquakes

For example, eruption of Vesuvius in 79 AD destroyed the city of Pompeii For example, eruption of Vesuvius in 79 AD destroyed the city of Pompeii

On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas. On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.

Pyroclastic flows of poisonous gas and hot volcanic debris engulfed the cities of Pompeii, Herculaneum and Stabiae suffocating the inhabitants and burying the buildings. Pyroclastic flows of poisonous gas and hot volcanic debris engulfed the cities of Pompeii, Herculaneum and Stabiae suffocating the inhabitants and burying the buildings.

The cities remained buried and undiscovered for almost 1700 years until excavation began in 1748. These excavations continue today and provide insight into life during the Roman Empire. The cities remained buried and undiscovered for almost 1700 years until excavation began in 1748. These excavations continue today and provide insight into life during the Roman Empire.

Vesuvius remains a hazardous volcano with heavily populated flanks: Vesuvius remains a hazardous volcano with heavily populated flanks: around 1.5 million people live in the city of Naples alone Naples is situated approx. 30 km from Vesuvius Pyroclastic flows can flow up to 100 km from source!

An eruption of Mt Peleé in 1902 produced a pyroclastic flow that destroyed the city of St. Pierre. An eruption of Mt Peleé in 1902 produced a pyroclastic flow that destroyed the city of St. Pierre.

Hot volcanic activity can melt snow and ice Hot volcanic activity can melt snow and ice Melt water picks up rock and debris Forms fast flowing, high energy torrents Destroys all in its path

It is not just explosive volcanic activity that can be hazardous. Effusive (lava) activity is also dangerous. It is not just explosive volcanic activity that can be hazardous. Effusive (lava) activity is also dangerous.

Iceland, January 23,1973. Iceland, January 23,1973. Large fissure eruption threatened the town of Vestmannaeyjar.

The lava flows caught the inhabitants by surprise The lava flows caught the inhabitants by surprise Before the eruption was over, approximately one-third of the town of Vestmannaeyjer had been destroyed

However, the potential damage was reduced by spraying seawater onto the advancing lava flows. However, the potential damage was reduced by spraying seawater onto the advancing lava flows. This caused them to slow and/or stop, or diverted them away from the undamaged part of the town.

So…. So…. How do we minimize the risk of active volcanoes?

Seismicity Seismicity Deformation Gas Output (on volcano and remote sensing techniques)

Earthquake activity commonly precedes an eruption Earthquake activity commonly precedes an eruption Result of magma pushing up towards the surface Increase volume of material in the volcano shatters the rock This causes earthquakes

“Tiltmeters” are used to measure the deformation of the volcano “Tiltmeters” are used to measure the deformation of the volcano The tiltmeters measure changes in slope as small as one part per million. A slope change of one part per million is equivalent to raising the end of a board one kilometer long only one millimeter!

Tilltmeters can tell you when new material enters the magma chamber. Tilltmeters can tell you when new material enters the magma chamber.

Commonly gas output from a volcano increases or changes composition before an eruption. Commonly gas output from a volcano increases or changes composition before an eruption. As magma rises to the surface it releases (exsolves) much of its gas content. This can be measured

Gas samples are collected from fumaroles and active vents. Gas samples are collected from fumaroles and active vents. Gas levels may also be monitored by remote sensing techniques

Volcanoes are extremely hazardous. Volcanoes are extremely hazardous. However, the volcano can be studied, monitored and understood. Each volcano is different, and offers a unique set of dangers Plans may be emplaced to help control potential damage.

What should geologists do about volcanic eruptions in the future? What should geologists do about volcanic eruptions in the future?

1,700 people living in the valley below Lake Nyos in northwestern Cameroon mysteriously died on the evening of August 26, 1986. 1,700 people living in the valley below Lake Nyos in northwestern Cameroon mysteriously died on the evening of August 26, 1986.

Lake Nyos is a crater lake inside a dormant volcano. Lake Nyos is a crater lake inside a dormant volcano. The lake had become laden with carbon dioxide gas. This gas had suddenly bubbled out of the lake and asphyxiated nearly every living being in the surrounding valley.

A management plan has been developed to remove gas from the lake to prevent a further tragedy. A management plan has been developed to remove gas from the lake to prevent a further tragedy. An artificial vent to the lake surface was created with pipe. Water is pumped from the bottom of the lake to the surface through the pipe, where it can degas.

The Lake Nyos incident was not unique. The Lake Nyos incident was not unique. Two years earlier, Lake Monoun, 60 miles to the southeast, released a heavy cloud of toxic gas, killing 37 people. A third lake, Lake Kivu, on the Congo-Rwanda border in Central Africa, is also known to act as a reservoir of carbon dioxide and methane, which is a valuable natural gas that is gathered from the lake and used locally.

Large volumes of magma moving through the shallow crust can cause large earthquakes. Large volumes of magma moving through the shallow crust can cause large earthquakes. This can lead to building collapse, slope failure and avalanches