"Are there volcanoes on Mars? Are there different kinds of volcanoes and what causes them? Are there active volcanoes in the Cascade Mountains? What happened to Mount St. Helens?"
Ash, Steam and Lava
The largest volcano in our solar system, Olympus Mons, is found in the Tharsis region on Mars. Olympus Mons (left) would cover the whole state of Washington and is 3 times higher than Mount Everest on Earth.
There are volcanoes on Venus and on one of the moons of Jupiter, Io.
Elysium Planitia is the second largest volcanic region on Mars. It is 1,700 by 2,400 km in size and is located on an uplift dome. The 3 large volcanoes, Hecates Tholus, Albor Tholus, and Elysium Mons, are smaller than those found in Tharsis but are still quite large. Elysium Mons is the largest volcano in this region, measuring 700 km across and rising 13 km above the surrounding plains.
We get the word "volcano" from the name of an island near Sicily in the Mediterranean Sea. People at the time thought that the steam, smoke and lava coming from the island was coming from the forge of Vulcan, the blacksmith of the Roman gods, who made the thunderbolts for Jupiter and weapons for Mars, the god of war. The term volcano now refers to an opening (vent) on the Earth's surface where lava and hot gases are released.
Volcanoes are grouped into types called cinder cones, composite volcanoes, shield volcanoes and lava domes.
Erupting volcanoes can be very violent because of the presence of extremely hot steam and gases or more stately with lava flowing slowly out of the vent. Cascade Volcanoes are found in the Cascade Mountains of Washington, Oregon and California. One of them, Mount St Helens, erupted in 1980 and several more are still somewhat active. Some volcanoes erupt under the ocean as vents open in the ocean floor. Explosive events sometimes occur because of hot lava mixing with sea water.
Scientists have developed a theory called "Plate Tectonics" to explain why volcanoes are usually found along the edges of continents and in mountains beneath the oceans. In this theory the continents float on the surface of the Earth on a continental plate and slide, collide or push other continental plates. The heat and pressure from this movement causes rock deep within the Earth to melt (magma) and force its way to the surface to create volcanoes. Plate movements are also believed to cause earthquakes. It is believed that at one time in the distant past all of the plates formed one huge continent called Pangea. In the diagram the yellow lines indicate plate boundaries and the red lines mark areas of volcanic action.
Click on image for a detail view of Main Continental Plates diagram.
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Here are some basic terms used in the tour. Find more geology terms in the Glossary.
- Fragments of less than 2 millimeters in diameter of lava or rock blasted into the air by volcanic explosions.
- Volcanic rock caused by partial melting of the Earth's crust.
- A large volcanic depression, commonly circular or elliptical when seen from above, caused by a volcano collapsing into itself.
- Cinder Cone
- A circular or oval cone made up of small fragments of lava from a single vent that have been blown into the air, cooled and fallen around the vent.
- Composite Volcano
- A steep-sided volcano composed of many layers of volcanic rocks, usually made from high-viscosity (thick like honey) lava, ash and rock debris (broken pieces).
- A steep-sided mound that forms when viscous (thick like honey) lava piles up near a volcanic vent (opening at the surface).
- A vent that releases volcanic gases and steam.
- A mixture of water and rock debris that forms on the slopes of a volcano. Also known as a mudflow or debris flow. The term comes from Indonesia.
- A light-colored volcanic rock containing lots of bubbles from trapped gases. This rock can sometimes float on water.
- Pyroclastic Flow
- A hot, fast moving and high-density (thick like a dust storm) mixture of ash, pumice, rock fragments and gas formed during explosive eruptions.
- Shield Volcano
- A volcano shaped like a bowl in the middle with long gentle slopes made by basaltic lava flows.
- An opening at the surface where magma, gas and steam erupt.
- A vent at the surface where magma, gas and steam erupt. Also, the landform constructed by volcanic material.
Kids' Cosmos… Expanding Minds Beyond the Limits of the Universe
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