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AND STILL MORE TYPES OF VOLCANOS!
We saw lots of volcanos in The Great Desert, but could not see every single different type (nor
might one really want to). Here are a few of the other types of landforms associated with volcanic
eruptions, but not necessarily a comprehensive list! An important one (possibly) for Mars is the
'tuya'
or table mountain landform, which forms when lava erupts into ice.
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Maar Craters |
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Maar craters form when molten lava, on its way to the surface, encounters lots of groundwater.
The resultant explosion makes a circular pit that resembles a meteorite crater. In fact, the first
geologist to investigate Meteor Crater (G.K. Gilbert) interpreted it as a maar. |
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| View from the rim of the Crater Elegante maar, across to the other rim. Looks a lot like an impact crater? In the background is part of the Pinacate shield volcano, dotted with cinder cones. Crater Elegante is in the Pinacate Biosphere Reserve in Mexico. Credit. |
This small deep maar is Ubehebe crater in
Death Valley National Monument.
Taken by Treiman many years ago, BWF (before wife and family). Credit.
Click here for other images,
including aerial views, of Ubehebe. |
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Flood Basalts |
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When huge volumes of basalt lava erupt rapidly, their flows spread out and no 'volcano' is formed
at all - just a huge flat plain of lava flow. Such huge effusions of lava are moderately common in
Earth's past, and apparently also on Venus and Mars. On Earth, these areas are commonly called "Large
Igneous Provinces." |
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This map (from the USGS) shows the extent of the Columbia River Basalts one of the smaller Large Igneous Provinces. The Columbia River Basalts cover 500,000 square kilometers, and are up to 2000 meters thick, for a total volume of near 170,000 cubic kilometers. Individual basalt flows can be followed for hundreds of kilometers. |
Aerial view of dry valleys cut into the Columbia River basalts, with the River itself in the far back right. All you see is basalt, and downwards for hundreds (or thousands) of meters. Image taken by Treiman in 1995 at the Mars Pathfinder conference. |
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Mid-Ocean Ridge Volcanism |
| Most of the Earth's surface is ocean floor, which forms at mid-ocean ridges and is carried away from them in the motions of plate tectonics. This, the most abundant form of eruption on Earth, forms broad flat plains and not the familiar cones of 'typical' volcanos. The lava flows on the seafloor have characteristic rounded lumpy masses, or 'pillows,' that form when the lava hits and flows into water." |
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Color topographic map of the Cleft mid-ocean ridge. Lava erupts along the highest portion of the rigde making pillow lava flows and piles of broken pillow debris. Map from web site link, from the NOAA. |
A road cut, about 10 meters tall, entirely of basalt pillows. They are the pill-shaped objects with light green cores and dark edges. This outcrop is in northern California. It is a piece of ancient seafloor that was scraped onto the North American continent in an ancient subduction zone (not subducting now). Credit. |
