Volcanic Hazards PDF

Volcanic Hazards What should you expect from this lesson? In this lesson we will: list and define the effects of volcanic gases, ash clouds, lava flows, pyroclastic flows and lahars on people and the environment describe the measures that can be taken to lessen the hazards of a volcano...

Volcanic Hazards What should you expect from this lesson? In this lesson we will: list and define the effects of volcanic gases, ash clouds, lava flows, pyroclastic flows and lahars on people and the environment describe the measures that can be taken to lessen the hazards of a volcano Volcanic Eruptions Volcanic eruptions are among the most spectacular and destructive natural events. They alter the environment, the weather as well as global climate, and they also affect millions of people who live close by. Boiling and bubbling lava is emitted from deep cracks in the rock and covers the land. Ash, smoke, steam and poisonous gases fill the air and pieces of rock are ejected from the crater causing serious damage wherever they fall. When volcanoes erupt suddenly, they can leave much destruction. The impact will be devastating on the people and the environment nearby. More than 200,000 people fell victim to volcanic eruptions in the past 500 years. An estimated 580 people perish from volcanic eruptions each year. There are several hazards produced by volcanic activity. Some of these include lava flows, lahars, pyroclastic flows, tephra, poisonous gases and tsunamis. Lava flows Lava flows. Large quantities of molten lava can be thrown out of the volcanic crater during an eruption. This flows down the slope of the volcano burning everything in its path, burying buildings and entire settlements and farmland. As can be seen in the next slide, lava from Mount Etna in Sicily forms a flow which moves down the slope of the volcanic mountain. These flows rarely leave victims but they bury and burn whatever lies in their path. In 1983, millions of tonnes of lava destroyed hotels, restaurants, sports facilities, houses and fields. The lava flowed at 15 km/hour and it was feared that it might destroy three hamlets that were in its course. To avoid this from happening, retaining walls were built and canals were dug. These successfully diverted the course of the lava flow away from inhabited areas. Lava flow from Mount Etna, Sicily The video below shows a lava flow on Mauna Loa volcano in Hawaii. Watch the lava flowing slowly and destroying everything in its path. https://www.youtube.com/watch?v=Hm8LQSoi0lI&t=1s Pyroclastic Flows Pyroclastic flows. These are superheated clouds of gas mixed with ash and rocks that flow down the sides of volcanoes at speeds of up to 200 km/hour. The gas can reach temperatures of about 1,000°C. They are a common and devastating result of certain explosive volcanic eruptions and are able to destroy everything in their path. The eruption of Mount Vesuvius in 79 AD is famous for the destruction of the two Roman cities that were buried under many tonnes of ash. The cities of Pompeii and Herculaneum were destroyed by a pyroclastic cloud of gas, ash and rocks with a temperature of over 200°C. The cities were totally buried and were forgotten until they were accidentally discovered in the 18th century. The pyroclastic flow from the Mount Pelée eruption on Martinique in 1902 killed 28,000 people. A pyroclastic flow can travel at a distance of 200 km/hour The video below shows how deadly pyroclastic flows can be. https://www.youtube.com/watch?v=N4-5kLbHY2Y&t=1s Lahars Lahars. These consist of volcanic mudflows of ash deposits, rock fragments and mud mixing with water. The water can originate from heavy rainfall or melting snow and ice on, or above, a volcano. Lahars can travel at speeds of up to 50 km/hour on a steep slope. Lahars can consume everything in their path, either destroying it or burying it under layers of debris. In 1985, the volcano Nevado del Ruiz in Colombia erupted suddenly. The hot gases and ash erupted from the volcano melted the ice which flowed rapidly downslope. This mud and ash avalanche buried the city of Armero where more than 23,000 people perished. Watch this short video clip of a lahar. Find out what they are, how quickly they move and what it is that makes them so dangerous. https://www.youtube.com/watch?v=xJriWzxBa_Q Tephra Tephra. Tephra is any material ejected by a volcano into the air. This can be anything from fine ash to large volcanic bombs. A volcanic bomb is a fragment of molten rock between 60 mm and 5 m in diameter which is ejected into the air during an eruption. Ash is the remnants of pulverised lava that measures less than 2 mm in diameter. Ash can be transported thousands of kilometres away by the wind. Ash fall can cause buildings to collapse and disrupt economic activity over a whole area. Tephra is hazardous as it can cover agricultural land, destroying crops. It can also cause airspace to be closed. The 2010 eruption of Eyjafjallajökull led to the cancellation of 100,000 flights. Ash-covered houses in Iceland Watch this short clip showing plumes of rock and ash thrown into the air by Mount Ontake in Japan. Hundreds of hikers were on the volcano at the time of the eruption. Most walked down to safety but others were trapped and 31 people died. https://www.youtube.com/watch?v=aQtkoLxqUNQ&t=3s Poisonous Gases Poisonous gases. Volcanic eruptions release a wide range of toxic gases that include carbon dioxide, carbon monoxide, and sulphur dioxide. These pose a silent and deadly threat to human life. When sulphur dioxide combines with water in the atmosphere acid rain is produced. This pollutes surface water, enhances weathering and can damage crops and forests. In 1986, an invisible cloud of carbon dioxide suffocated 1,742 people and 3,000 cattle in Cameroon. Volcanic Eruption Prediction Volcanologists attempt to forecast volcanic eruptions with the help of satellites, lasers and computers. Very often a volcano that is about to erupt may produce a sequence of earthquakes. Volcanologists use seismographs to record such earthquakes to try to determine if an eruption is imminent. Most volcanoes tend to swell close to an eruption. However, ground deformation can only be observed by special instruments. Increase in the emissions of gases indicate that a volcano is about to erupt. Scientists regularly measure gas emissions in vents and around the volcano to help predict eruptions. The build-up of magma inside the volcano causes the ground surface temperature to rise. This is monitored using satellite technology and if it rises considerably it will be evident that an eruption is likely to occur. Nothing can be done to prevent a volcanic eruption. A range of methods are available to give an early warning and reduce the impact of volcanic hazards. The video below explains the different ways volcanologists are able to record warning signs of a possible eruption. https://www.youtube.com/watch?v=Zkbnn7SVATE&t=1s