SkillBuilder discussion Geographical inquiry 1. Describe the different types of materials that can be erupted from a volcano. 2. Evaluate which type of eruption would be the most dangerous. 3. Explain why lahars would be linked to ice-covered volcanic peaks.
FIGURE2 The anatomy of a volcano
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A A fragment of lava greater than 64 millimetres in diameter is called a volcanic bomb. They are often solid pieces of lava from past eruptions that formed part of the cone. B A pyroclastic flow is a superheated avalanche of rock, ash and lava that rushes down the mountain with devastating effects. The flow can travel at up to 240 kilometres per hour and reach temperatures of 800 ° C. When Mount Pelée erupted in 1902, on the island of Martinique in the Caribbean, a pyroclastic flow covered the town of Saint-Pierre, killing all but two of the town’s 30 000 inhabitants. C Lightning is often generated by the friction of swirling ash particles. D As rock is pulverised by the force of the eruption, it becomes very fine ash, and is carried by wind away from the crater as an ash cloud. Volcanic ash may blanket the ground to a depth of many metres. In the eruption of Mount Vesuvius in 79 CE, volcanic ash completely covered two large towns: Pompeii and Herculaneum. E A volcanic cone is made up of layers of ash and lava from previous eruptions. If the volcano has not erupted for thousands of years (i.e. is dormant), these layers will be eroded away. F Lava may be either runny or viscous, and can flow for many kilometres before it solidifies, thereby building up the Earth’s surface. G Pressure may force magma through a branch pipe or side vent. In the eruption of Mount St Helens in Washington in the United States, in the 1980s, the side of the mountain collapsed and the side vent became the main vent. H Where two plates move apart, molten rock from the mantle flows upward into a magma chamber. More rock is melted and erupts violently upwards. Magma is generally within the temperature range of 700 – 1300 ° C. I When pyroclastic flows melt snow and ice, and mix with rocks and stones, a very wet mixture called lahar can form. Lahars can flow quickly down the sides of volcanoes and cause much damage. One lahar that formed in 1985 on the Nevado del Ruiz volcano in Colombia travelled at up to 50 kilometres per hour and was up to 40 metres high in some places. A wall of mud, water and debris travelled 73 kilometres to the town of Armero, devastating it. More than 23 000 people died that night and 5000 homes were destroyed.
404 Jacaranda Humanities Alive 8 Victorian Curriculum Third Edition
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