in aVOLCANIC ERUPTION

Pyroclastic flows / surges• They are mixtures of pulverized

rock, ash, and hot gases from the volcano, formed when magma interacts explosively with water.

• Pyroclastic flows can move at speeds of hundreds of miles per hour (650mph) and are hundreds of degrees (400°c)

• They destroy everything in their path by crushing or burning – they cannot be escaped.The 1980 Mount St Helens (Washington, USA) eruption killed 57 people. Those closest to the eruption fell victim to the landslide and pyroclastic blast that was triggered by an earthquake. The pyroclastic flow of very hot volcanic gases, ash and pumice formed from new lava, while the pulverized old rock hugged the ground reached speeds as high as 670 mph (and may have even broken the sound barrier). It spread outward, devastating a fan-shaped area 23 miles across by 19 miles long; 230 square miles of forest was knocked down.

Lava flows• Lava is molten rock that flows out

of a volcano or volcanic vent. • Can have a high or low viscosity -

fluid flows are hotter and move faster than viscous flows, which are cooler and travel shorter distances.

• Lava flows generally travel slowly and can be easily avoided by a person on foot, but cannot be stopped or diverted.

• Lava flows are extremely hot - between 1,000-2,000°C – so can cause severe burns and burn down vegetation and structures. The volcano is monitored by the United States Geological

Survey(USGS) who have an observatory on the Kilauea crater rim. Lava flows are the main volcanic hazards and VOG- volcanic gases mixing with clouds or steam. Lava flows are currently flowing from Kilauea but it is Mauna Loa which poses the biggest risk to the largest settlement in the South- Hilo. Currently lava flow hazard areas are mainly on the south

Volcanic ash & tephra• Made up of a range of rock

particles; different shapes sizes and types - combinations of pumice, glass shards, crystals, minerals, and shattered rock.

• Ash falls cover everything, infiltrates most openings, and is highly abrasive.

• Airborne ash can obscure sunlight, creating zero visibility.

• On roads can become slippery when wet, posing risk to vehicles.

• Automobile and jet engines may stall from ash-clogged air filters, and moving parts can be damaged from abrasion.

• Roofs may collapse under the weight of deposited ash

• Farmland covered and plants smothered

• Power systems may shut down and waste water clogged

May 18, 1980 eruption of Mount St. Helens covered areas in ash 180 miles from the volcano. Ash covered homes, farms, and roads to a depth up to four-inches.

Volcanic gases• Magma contains dissolved gases

that are released into the atmosphere during eruptions.

• Gases are also released from magma that either remains below ground rising toward the surface, like volcanic vents, fumaroles, and hydrothermal systems.

• Vog contributes to breathing problems and acid rain damages crops and corrodes facing stones on buildings and damages metal.

• C02 emissions and sulphur dioxide can also affect the ozone layer. Whilst most of the time lava merely oozes out of volcanic vents in Hawaii, Sometimes clouds of steam and sulphur dioxide rise from Kilauea volcanic system. The regular release of gas since 1983 has created volcanic smog, ‘vog’ and acid-rain conditions on the Big Island of Hawaii.

Seismic activity• Areas of volcanic activity are

usually in areas of earthquakes, or are prone to earthquakes triggered by volcanic eruptions.

• This could lead to general impacts of earthquakes, such as building collapse, land deformation and cracks.

• Earthquakes tend to happen before a volcanic eruption, so could be taken as an early warning to evacuate the area.

Chances Peak in Monteserrat, a small Caribbean island, had been dormant for over 300 years. It erupted in 1997, preceded by earthquakes – these were recognised as a sign of volcanic pre-eruption the small population of the island (11,000 people) was evacuated in 1995 to the north of Montserrat, neighbouring islands and the UK. However 19 people died, who had riskily decided to stay. In many other cases, the earthquakes that come before volcanic eruptions have acted as a warning indicator and allowed people to get to safety.

Debris, avalanches & landslides• Caused by intrusive magma

chamber collapse, earthquakes, or explosive volcanic erruptions.

• Landslides commonly originate as massive rockslides or avalanches which disintegrate during movement If the moving rock debris is large enough and contains a large content of water it could lead to the formation of mudslides and lahars.

• The obvious hazards of landslides are the enormous power and speed at which the material will travel – covering or destroying everything in its path. Landslides into the sea may also cause tsunamis.

The landslide at Mount St. Helens on May 18, 1980, had a volume of 2.5 km3, reached speeds of 50-80 m/s (180-288 km/hr), and surged up and over a 400 m tall ridge located about 5 km from the volcano.

Jokulhlaup• Sudden, violent discharge of

glacial meltwater. Jökulhlaups occur when glacier ice dam bursts creating a large but quick flood, usually triggered by volcanic eruptions. 

• Risks of Jokulhlaups are roughly similar to severe flash flooding risks – flooding settlements, carrying debris, and damaging roads etc.On the 14th of April in Iceland, Eyafjallajökull’s explosive eruption caused melting through the 200 m thick ice cap within hours. The rapid melting of the ice cap produced volcanogenic jökulhlaups that cascaded on the northern and southern flanks of the volcano. The flood reached damaged Iceland’s ring road, and the town Markarfljót was evacuated.

Lahar• A lahar is a mudflow of debris

containing pyroclastic material, rocky debris, and water flowing down from a volcano. It can carry sediment as large as boulders, and tears through vegetation and the land and can grow to 10 times their original size.

• Lahars are triggered by volcanic eruptions quickly melting snow / ice on a volcano, ejecting water from a crater lake, but more often are due to intense rainfall that loosens material on volcanic hillsides

An explosive eruption from Nevado del Ruiz, Colombia, in 1985 sent a series of pyroclastic flows and surges across the volcano's broad summit. The pyroclastic flows and surges quickly eroded and mixed with Ruiz's snow and ice. Flowing mixtures of water, ice, pumice and other rock debris then poured from the summit and sides of the volcano into rivers draining the volcano. lahars had travelled 100 km and left behind a wake of destruction: more than 23,000 people killed, about 5,000 injured, and more than 5,000 homes destroyed.