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Which natural phenomena do you think present the greatest challenges to humans? About 240 millions years ago, all the land on the earth’s surface was joined together in one vast supercontinent that extended from pole to pole. But by 18,000 years ago, the earth had been transformed; the continents as we know them today had been created and had moved into their present positions. But the Erath’s surface has not stopped moving and the process continues today. Why does this movement occur? Deep within the earth, pressure and heat cause rocks of the mantle to become partly molten, but near the surface a thin layer of solid rock forms the crust. As currents of heat rise and fall within the mantle, the crust breaks up into large pieces, called plates, which move about very slowly on earth’s surface. The movement of the plates creates powerful forces that continually create and destroy land features and reshape the earth’s surface. Most of the action takes place at the plate edges, or boundaries, where plates move against or over each other, or dive back below the surface. As the plates move, mountains are uplifted, the sea floor cracks and spreads, volcanoes erupt, and new land is formed. I think that volcanoes present the greatest challenges to human. And I will try to explain my point of view. As I have already mentioned volcanoes can form a new lands, without them we would not have Hawaii Iceland and many other most magnificent places in the world. On the other hand, volcanic eruptions are one of the most destructive natural disasters, which endanger human life and cause significant changes in the atmosphere. A large eruption can be extremely dangerous for people living near a volcano. Flows of searing lava, which can reach 2,000 degrees Fahrenheit (1,250 degrees Celsius) or more, can be released, burning everything in its path, including whole towns. Boulders of hardening lava can rain down on villages. Mud flows from rapidly melting snow can strip mountains and...