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8. Volcano hazards
Material expelled with the eruption is the most direct hazard associated with volcanoes. This includes ash and lava itself. If the volcano explodes outward (rather than upward) a dense cloud of fiery gases, molten and solid rock will descend the hillside as a pyroclastic cloud, eliminating all in its path. If the mountain top is covered in snow, eruptions will cause rapid melting and the mixture of ash, soil and water moves downhill as a mudslide or lahar.One of the most dramatic effects of a volcano occurs in the ocean. If a volcanic island explodes the effects of the explosion are transmitted though the ocean basin as a wave. In 1883 an uninhabited island in Indonesia called Krakatoa erupted. It was the biggest eruption in recorded history and was heard from almost 5000 km away, in Australia. The north part of the island that stood 600 m above sea level disintegrated. The tidal waves that resulted killed more than 36,000 in Java and Sumatra. Recently a scientist has warned that an eruption and accompanying landslide on the island of La Palma in the Canaries would produce a massive wave in the Atlantic basin. This tidal wave would be 40-50 metres high when it reaches the eastern American coast. In low-lying areas the sea would move 10-12 km inland.
Finally, volcanoes effect the world's weather. Ash, suspended in the atmosphere, can block out sunlight from the surface. If a large number of eruptions were to occur simultaneously a blanket of ash could surround the earth, causing a dramatic decrease in temperatures.
Learning more
Again, there are many sites dedicated to natural disasters in general and vulcanology in particular. Here is an excellent volcano site that has information on specific volcanoes from around the world.
