VOLCANOES OUTSIDE EARTH
Olympus Mons
When people think or talk about volcanoes we tend to relate to familiar names or incidents such as Mt. St. Helen's and the eruption of 1980. Historians as well will note past incidents such as Vesuvius and the burying of Pompeii or other older events. In fact, information has been compiled and documented quite thoroughly over the years around our planet. But we must ask ourselves if that is where it ends. Are volcanoes exclusively an earthly geographic phenomenon ? Or may vulcanologists and amateur observers look elsewhere for evidence ? Perhaps to the heavens.
In fact with the aid of satellites and more powerful observation equipment scientists have been able to determine that the properties and characteristics we have come to associate with our own planet are often found on other bodies of the solar system. For example Venus and Jupiter also have thick atmospheres though they do consist of differing gas mixtures. Venus also holds water vapour in its atmospheric mix like Earth and Mars has canals. Other planets receive meteor showers similar to Earth as well. But what about volcanoes. Have they been discovered elsewhere.
Indeed they have. It was once assumed that Mauna Loa, the mountain that partly makes up the island of Hawaii, was the largest and most imposing example of a volcano known to man. However, the dimensions of that fearsome natural wonder have been surpassed by the discovery of Olympus Mons, a gigantic shield volcano similar to Mauna Loa, on the planet of Mars.
This image shows the volcano Olympus Mons. With a diameter of more than 600 kilometers (the size of Arizona) and a height of nearly 25 kilometers above the surrounding plains, it is the tallest volcano known to exist in the solar system. When clouds are present, it is sometimes even visible above the clouds.
The relative ages of the surface in various parts of Mars can be estimated from the number of impact craters present in a given area, with young regions having fewer craters than old regions. Only two craters are visible here,indicating that Olympus Mons is young, probably the youngest volcanic feature on Mars. By some estimates, the most recent large volcanic eruption at Olympus Mons occurred only 25 million years ago. The oldest activity at Olympus Mons could be much older than this and would have been buried by younger lava flows.
The caldera of Olympus Mons is the depression near the top center of the image. The caldera is about 65 x 80 kilometers across (the size of Rhode Island) and occurs near the maximum elevation of the volcano. It formed when magma within the volcano either erupted out of vents on the side of the volcano or temporarily drained deeper into the planet. In either case, the removal of this magma allowed part of the overlying surface to collapse, producing a topographic depression that is termed a caldera. The overlapping series of structures in the Olympus Mons caldera demonstrates that this magma withdrawal occurred a number of different times. Similar calderas are seen on other volcanoes both on Mars and on Earth. (Viking Orbiter image 641A52.)
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