A volcano is an opening on the surface of a planet that allows material warmer than its surroundings to escape from its interior. When this material escapes, it causes an eruption. An eruption can be explosive, sending material high into the sky. Or it can be calmer, with gentle flows of material. However, volcanoes are just an opening usually on a mountain in the Earth surface from which gas, hot magma, and ash can escape but volcanoes are formed because of the movement of plates (convergent boundary to be exact).
Mount Ruapehu
Mount Ruapehu is one of the world's most active volcanoes. Recent major eruptions occurred in 1895, 1945, 1995, 1996 and 2006.
The 1945 eruption had far-reaching effects, resulting in the loss of 151 lives on December 24th, 1953. When the eruption occurred the crater lake was emptied, and the outlet dammed. Over time the crater refilled and the dam collapsed causing a lahar (mudflow and water) in the Whangaehu River. The lahar undermined the Tangiwai railway bridge piers, and the bridge collapsed when an express train crossed it.
Through 1995 and 1996 Mount Ruapehu erupted several times closing the ski fields and occasionally the airports. The possibility of a major lahar occurring again was recognised as the crater lake outlet became blocked once more in 1996 by volcanic ash. Authorities are constantly monitoring the volcano and determining measures of safely controlling the situation, should the dam brake again.
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