Planet Building Our solar system has reached middle age, and so have the planets in it. Like any middle-aged thing, activity levels are not what they used to be.
For Earth, that means less impressive volcanism, among other things. But in Hawaii and a few other hot spots around the globe, somewhat puny vestiges of the fire and brimstone that once helped
forge continents still rage in their own small way. In fact, right now, the Big Island is growing.able -->  |
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 | Galileo imaged the Prometheus volcano on Io, with a caldera and lava flowing through fields of sulfur dioxide snow. Scientists said it is remarkably similar to the Kilauea volcano in Hawaii, though Prometheus is much larger.
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| Olympus Mons is taller than any terrestrial volcano. Mars Global Surveyor captured this view in 1998.
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| Lava from Hawaii's Kilauea volcano flows down a scarp that was previously cut by a wave. The lava heads toward the water in this Sept. 3 photograph.
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| The lava reaches the water. Steam forms constant acidic plume hazardous to your health. It also adds land to the island over time.
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|  | TODAY'S DISCUSSION | | |
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Hawaii's Kilauea volcano has been erupting off and on since 1983 in what scientists say is one of its most voluminous outpourings of lava in centuries. It has wiped out nearly 200 structures and covered more than 8 miles (13 kilometers) of road.
The lava has also added more than 495 acres (200 hectares) to the island's southern shore.
The lava starts its journey to the sea 6 miles (10 kilometers) from shore. It flows on the surface and through underground tubes. The rivers of hot molten rock have built countless new deltas jutting into the surf, some growing to the size of a football field or larger in less than a week. Waves splash over the oncoming lava, it cools quickly and then typically shatters into sand and fragments up to the size of basketballs. Material accumulates underwater and forms a loose foundation that eventually supports more lava that flows atop it, creating the new land.
With other volcanoes, the landscape can change in the blink of an eye. When Mount St. Helens erupted in 1980, an avalanche of debris traveled 15 miles (24 kilometers) and generated enough material to cover Washington, D.C. to a depth of 14 feet (4 meters).
But volcano-inspired landscaping in the Western United States, Hawaii and elsewhere on the planet is nothing compared to what Earth's internal heat engine can do over longer, so-called geologic periods of time.
Other than a few catastrophic eruptions and some notable lava flows, real change is almost always too small for people to observe in a lifetime, says Scott Rowland, a volcano researcher at the University of Hawaii. "But over thousands, tens of thousands, and hundreds of thousands of years, large topography-altering structures are built."
On the early Earth, volcanism was far more widespread and intense.
"In that period of time, way more happened than we can really appreciate," Rowland says. "By comparison, the current eruption of Kilauea is pretty miniscule."
Around the solar system
Earth is not the only place where volcanic activity builds and destroys the surface.
Many of Mars' most dramatic features, such as long, deep structures that dwarf the Grand Canyon, might have been formed by
catastrophic flows of water or carbon dioxide pushed from higher ground by ancient volcanic eruptions, some geologists suspect.Mars is only about half the size of Earth, yet it has several volcanoes -- all thought to be dormant or dead -- that are bigger than the largest terrestrial volcanoes. Olympus Mons is 15 miles (24 kilometers) tall. The largest volcano on Earth is Mauna Loa in Hawaii at 6 miles (9 kilometers), a figure that includes the portion of the volcano that extends underwater to the sea floor.
"It is quite likely that plate tectonics, and its associated volcanism, will continue here on Earth for a long time [perhaps billions of years], whereas Mars has essentially shut down volcanically," says James Zimbelman, a geologist at the Smithsonian Institution who studies lava flows on Earth and other solar system bodies.
On Jupiter's moon Io,
volcanoes still rule, and there are some similarities to what goes on in Hawaii. The innermost Jovian satellite is the most volcanic body in the solar system. About three dozen active volcanoes scar the moon and pump rocky ash up to 62 miles (100 kilometers) above the surface."Volcanism on early Earth may actually be more similar to current-day volcanism on Io than volcanic activity on early Mars," Zimbelman said. Some lava flows on Io, he said, are similar to some seen on Earth.
Io, about the size of Earth's Moon, also has a hundred or so towering mountains or plateaus, and 300 basin-shaped calderas, or collapsed regions. Some of Io's calderas are more than twice as big as the Yellowstone caldera. The moon has mountains that soar 50,000 feet (16 kilometers) above the surface. The highest point on Earth is Mt. Everest in the Himalayas, at 29,022 feet (8.8 kilometers).
These tall mountains of Io might not actually be the result of volcanoes, however. Instead, scientists
speculate they could be formed by large blocks of Io's crust crunching together as they're pushed up by a mushy ocean of hot magma.Because volcanic activity and associated thermal vents on sea floors is now known to support living organisms in otherwise inhospitable places, biologists increasingly view volcanism as critically important to life. Volcanic activity also plays a significant role in the recycling of important organic chemicals from the air to the inner planet and back into the atmosphere.
"Volcanism probably is the next most important process in the solar system, after impact cratering, in terms of shaping the terrain and the biology," Zimbelman said.
Death and destruction
Earthlings are lucky they don't have to deal with the violence of Io. Yet volcanoes do kill people. Some 20,000 died in 1669 in Sicily, when Mount Etna (which began erupting again last year) sent a river of lava through the streets of Catania.
More recently, Mount Pinatubo killed 750 people in 1991. Among the victims were several journalists who kept vigil in a restricted area waiting for the eruption, which had been forecast for days.
While predicting volcanic activity proves challenging, Pinatubo and other less deadly eruptions have shown that experts are getting better at forecasting catastrophic events, or at least spotting early signs that something might happen within days or weeks. Satellites play a
crucial role in monitoring the 600 or so active volcanoes on Earth. With sensitive space-based instruments, researchers can spot minor bulges in a mountainside that sometimes presage major activity.Meanwhile, Hawaii's Kilauea provides a relatively safe natural laboratory for volcano study. Not completely safe, though.
As the lava touches the sea, a hazardous acidic plume rises into the air. And newly crafted lava land can collapse into the sea with little warning, sometimes generating explosions that splatter lava and large rocks into the air and send scalding water ashore.
In 1993, several visitors to the Hawaii Volcanoes National Park tried to get a close-up look of some delta-building. The leading edge of the delta collapsed and one visitor was never found. Others suffered minor injuries when lava hit seawater, exploded, and showered them with debris. Some people were injured as they fell while trying to flee.
Geologists know to keep a safer distance from the lava flows. And they take a lot of photographs of all this planet building. See our
gallery of images
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