However, the most impressive volcanic landforms are associated with the extensive, hotspot-related uplifts of Tharsis and Elysium plateaus. The volcanic features described below include the giant central volcanoes, peterae, tholi, and rootless cones. The most spectacular volcanic features on Mars are the isolated, giant basaltic shield volcanoes called Montes singular Mons , Latin for mountain.
The largest of these are four giant shield volcanoes associated with Tharsis uplifted region for a close-up view of two of these, double-click Tharsis Shields. All four dwarf the Mauna Loa shield volcano , the largest mountain on earth. The largest of the four is Olympus Mons , shown in the image here. These large basaltic shield volcanoes contain large central calderas and gentle slopes that extend outward at angles usually less than five degrees.
The volcano flanks have radial surface textures formed from lava channels and long narrow flows. The slopes of Olympus Mons dip gently away from its central caldera The flanks of Olympus Mons are composed of radial lava channels and long, narrow lava flows The large scale of the Tharsis shield volcanoes suggests that they formed from massive eruptions of fluid basalt over prolonged periods of time.
Similar eruptions on earth are associated with flood basalt provinces and mantle hotspots. However, on earth the source region for hotspot volcanism moves laterally as lithospheric plates travel across the stationary mantle plumes beneath them.
Without this mechanism of lateral movement, the Martian surface remains above the plume source so that huge volumes of lava will erupt from a single central vent over many millions of years of activity, thus generating a single shield volcano of enormous volume.
With this in mind, it is interesting to note that the volume of Olympus Mons is roughly equivalent to the total volume of basalt in the Hawaiian-Emperor seamount chain.
Compared with the Mons volcanoes, Tholi and Peterae are much smaller volcanic vents. A Tholus volcano is an isolated domal mountain with a central crater, having slopes that are usually steeper than those associated with both Mons and Peterae volcanoes.
A Patera volcano is dominated by an irregular or complex caldera with scalloped edges, surrounded by very gentle slopes of usually less than one degree. By studying six nakhlite meteorites from Mars previously established as volcanic, scientists confirmed the extensive lifetime of Martian volcanoes. We found that the nakhlites formed from at least four eruptions over the course of 90 million years," Benjamin Cohen, a planetary scientist at the University of Glasgow in Scotland, said in a statement.
The meteorites were blown into space when a massive rock crashed into the planet 11 million years ago. Another group of 11 Martian meteorites revealed that the volcanoes were active even longer. While 10 were only million years old, an eleventh, NWA , was found to be 2.
The volcanoes in Tharsis Montes are so large that they tower above the seasonal Martian dust storms. Italian astronomer Giovanni Schiaparelli , who studied the Martian surface intensively in the late 19th century, observed the enormous features from Earth using an 8-inch 22 centimeter telescope.
When NASA's Mariner 9 arrived at the red planet in , it was able to pick out the tops of the volcanoes above the storms. While no rovers have yet made the trek to the Martian mountains, that hasn't stopped many from dreaming about exploration. So while it might be awhile before you can physically climb the massive volcano, you may be able to at least explore it visually. In fact, some scientists have used the High Resolution Stereo Camera installed on the European Mars Express orbiter to create a mosaic and terrain model of the volcano.
Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community space. Nola Taylor Tillman is a contributing writer for Space. She loves all things space and astronomy-related, and enjoys the opportunity to learn more. In her free time, she homeschools her four children.
Follow her on Twitter at NolaTRedd. Nola Taylor Tillman. The explosions happen because as magma rises near the surface, the pressure keeping the water and gases dissolved goes away. Lowered pressure causes the gases to form bubbles in the magma. If enough gas is dissolved in the magma, this can cause a runaway effect.
At that point, the superheated water vapor and gases burst out of the lava like popping the top of a soda can after shaking it. The eruption of Mount St. Helens occurred in this way, after an earthquake shook off the volcano's upper part and exposed gas-rich magma. Most Earth volcanism is basaltic. Basalt bah-SALT is an igneous rock rich in iron and magnesium minerals.
It is usually dark gray or black. The most iron-rich basalts erupt at high temperatures and flow easily, like maple syrup. When magma has more silica in its composition, however, it moves stiffly, like cookie dough or peanut butter. Being thicker and stickier, high-silica magmas make it difficult for gas bubbles to escape smoothly once they form.
Again, this makes explosive eruptions more likely. Volcanic eruptions on Mars have built numerous kinds of features. The main types of features are what scientists call shield volcanoes and flood basalts. These volcanic features also occur on Earth, although the Martian versions have some differences.
Basalt flows are the most common kind of flow on Earth, and they are widespread on Mars as well. But because Mars is a smaller planet with less gravity and a thin atmosphere, its volcanic activity does not exactly match that of Earth. Flows also tend to go farther because the thinner atmosphere means they cool more slowly. In addition, the lower gravity and thinner atmosphere means that volcanic ash thrown from explosive eruptions likewise travels farther and spreads out more.
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