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January 15, 2004

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Volcanism on Other Planets

Since the beginning of the New Year, much attention has been focused on Earth's celestial neighbor, the planet Mars. Though the main goal of the current missions is to find evidence for past Martian life, we volcanologists are also watching developments on Mars with great enthusiasm. Mars is home to the largest volcanoes known to science and is one of just a handful of places in the solar system known to have any volcanoes at all.

Mars is only about half the size of Earth, but it actually has more exposed land area, since more than two thirds of Earth is covered by the oceans. Two gigantic regions of great uplift, called domes, stand out from the Martian surface. The larger of the two, the Tharsis Dome, is 4,000 km (2,500 miles) across and rises to nearly 10 km (6.2 miles) in height. Arranged neatly into a line, three large volcanoes, Ascraeus Mons, Pavonis Mons and Arsia Mons, mark the northwest edge of Tharsis. But, the real monster lies just beyond the Dome's northwestern boundary.

Olympus Mons towers 24 km (16 miles) over the Martian surface, utterly dwarfing the terrestrial Mount Everest, which reaches just under 9 km (5 miles) high. This gargantuan volcano is classified as a shield volcano and is, in many ways, similar to our own Mauna Loa, which is the largest volcano on earth, stretching 120 km (75 miles) across. By comparison, the diameter of Olympus Mons is more than 550 km (340 miles)!

Why do Martian volcanoes grow so large? The reason is two fold. First, Mars is not thought to have active plate tectonics, which means that the surface of Mars is very static. So, unlike in Hawaii where the Pacific plate is slowly but relentlessly moving Mauna Loa away from the fixed hotspot, a volcano on Mars can bask in the heat of a hotspot for long stretches of time, growing ever larger.

The second reason that Mars can sport mountains so massively large and monstrously high is that Martian gravity is only about one third as strong as Earth's. Martian volcanoes can grow much larger than their terrestrial counterparts before they begin to suffer from gravitational collapse.

Mauna Loa may not be as large as Olympus Mons, but it is certainly much more active. Determining the age of a Martian volcano is not easy, especially since no rock samples have yet been obtained (extremely rare meteors thought to have come from Mars do exist, but none is known to have originated from Olympus Mons). A few clues are in the offing, however. For example, very few impact craters indent Olympus Mons, strong evidence that the volcano is no more than 1 billion years old. Some planetary geologists argue that Olympus Mons may be only a few hundred million years old--young enough that Mars may not be volcanically dead.

In addition to Earth and Mars, Venus is also thought to have volcanoes, though there is no evidence for recent activity. To find volcanoes that are erupting today, one can of course stay home and enjoy the thousands of active volcanoes on Earth. The more adventurous and travel-minded volcanologist will be drawn to Io, a large moon of Jupiter. Ounce for ounce, Io is probably by far the most volcanically active place in the entire solar system.

Tidal forces from Jupiter's intense gravitational field are squeezing and stretching Io to such an extent that frictional heating in Io's interior causes large scale melting. The molten material, being less dense than its solid surroundings, forces its way to the surface and erupts spectacularly to heights of more than 100 km (60 miles).

Not surprisingly, scientists that study volcanism on other planets and moons in the solar system routinely visit the Big Island to learn about our volcanoes. Hawai`i has often been called a great natural laboratory of international significance. Over the last few decades, that significance has passed beyond international into the realm of the interplanetary.

Activity update

Eruptive activity at the Pu`u `O`o vent of Kilauea Volcano continued unabated during the past week. Fresh lava from vents within Pu`u `O`o coat the crater floor, and occasional spatter can be seen above the crater walls. Both the West Gap Pit vents located immediately outside the crater and the rootless shield complex at the top of the Mother's Day Flow were active throughout the week. Glow from flows within the crater and the overturning perched ponds of the shields light the night sky. No active flows are on Pulama pali or the coastal flat below Paliuli. No lava is entering the ocean.

No earthquakes were felt on the island during the week ending January 14.

Mauna Loa is not erupting. The summit region continues to inflate. Seismic activity remains very low, with 1 earthquake located in the summit area during the last 7 days. Visit our website ( for daily volcano updates and nearly real-time earthquake information. skip past bottom navigational bar

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Updated: January 29, 2004 (pnf)