Anonymous asked in Science & MathematicsEarth Sciences & Geology · 1 decade ago

What caused Mount Ruiz to erupt in 1985?

What's the geography behind it - What caused the small steam eruptions and minor earthquakes that led to the huge eruption?

1 Answer

  • 1 decade ago
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    Mount Ruiz is located in the Andes chain of mountains, within the Pacific Ring of Fire. On the Pacific Coast of South America, the Nazca plate is subducted beneath the continental South American plate. The Nazca plate slides beneath the South American plate, into the mantle where it starts to melt. The melting of the rock and crystals that make up the plate produces magma which rises beneath the South American plate, through cracks and reach the surface at various points which are volcanoes. Mount Ruiz is just one of these places where the magma produced from the melting of the Nazca plate erupts.

    The small steam eruptions are a result of the magma rising through the crust and coming into contact with water collected within it. As it is under pressure from the rock and the heat, it effectively explodes upwards and through the crust, creating the eruption.

    The minor earthquakes could be created for a variety of reasons. One reason could be because of the Nazca plate moving against the South American plate. Because this sliding action is a jerky, random motion, friction between the plates can produce earthquakes. However, this is usually at the ocean ridge where the two plates meet at the surface. Also, the earthquakes produced are usually a lot stronger than those recorded in the days running up to the eruption. Another reason could be rising magma meeting obstacles in its path as it rises. Magma rises at considerable speed and force and so when it meets an obstacle such as a rock blocking the path, it will slam into it. Sometimes it will break through without any recorded motion, but when the rock is hard enough to prevent the magma rising any further, the collision is sometimes strong enough to produce minor earthquakes. As an eruption nears, these earthquakes will become more frequent as there is more magma rising and potentially more producing collisions.

    The actual eruption was very gaseous and involved very little surface magma (lava). It was the pyroclastic flows and overall heat generated that combined with the loose material on the volcano's flanks that caused the devastating lahars.

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