Island of fire: do volcanoes send out warnings before popping their lids? Scientists study toxic gases in search of answers.
This fiery volcano has been gushing lava (erupted molten rock) for more than 20 years. That can be risky for nearby residents. In 1990, towering flows blanketed a seaside village with 15 meters (50 feet) of lava. Despite the occasional devastation, volcanoes are hot real estate. About 500 million people live within reach of the world's roughly 50 active (currently erupting, or showing signs that it may soon erupt) volcanoes.
How to keep residents safe from Earth's fiery landscape? Edmonds and other volcanologists (volcano scientists) are taking advantage of Kilauea's long-lasting eruption to study a volcano in action. By learning more about Kilauea's searing science, Edmonds hopes to be able to better predict other volcanic eruptions.
From the chopper, Edmonds treks over the sugar-textured pahoehoe (pah-hoy-hoy) lava. Her destination: a crater (basinlike depression) near Kilauea's summit. Every day, masses of lava--equal to the payload of about 45,000 dump trucks--gush from vents, or openings, in this crater.
Hopefully, Edmonds's hike hasn't left her breathing heavily. At the crater rim, she becomes engulfed in the vent's smelly gases. The gassy haze contains sulfur dioxide (S[O.sub.2]), a toxic gas. "When you inhale the gas, it reacts with water in your throat to form sulfuric acid [strong acid used in some batteries], creating a burning feeling," says Edmonds. Luckily, her gas mask filters out the toxic gas.
But for residents of the Big Island, where Kilauea sits, the smoky air can be unhealthy. "Kilanea pumps huge amounts of gases [called volcanic smog, or vog], into the air," says Edmonds. The vog, she says, can cause headaches and breathing difficulties for nearby residents.
Edmonds thinks that one way to help predict when a slumbering volcano will stir is to determine the depth of its underground magma (mixture of molten rock and dissolved gases). But a sizzling journey to Earth's mantle (layer between Earth's crust, or outer layer, and its innermost core), where magma forms, is possible only in science fiction movies. Instead, Edmonds uses a shoebox-size instrument to measure the gases.
How might these gases reveal eruption secrets? Kilauea's magma contains dissolved gases. And as the magma rises from the mantle, the pressure (force applied over an area) on it decreases. Result? Some gases expand and escape as bubbles from the jellylike fluid. Edmonds has found that each gas escapes at a certain pressure. By measuring the seeping gases, she hopes to pinpoint the underground magma. "If sulfur dioxide [which escapes from magma at shallow depths] levels shoot up at the surface, that could mean magma is rising to the top," says Edmonds. She says her study could give warnings months before an eruption.
Kilauea's current warning sign: "Usually, about two hours before an eruption, there will be a swarm of earthquakes," says Donna O'Meara, a volcano researcher in Hawaii. These earth-shakers signal the slothful rise of underground magma.
For Kilauea, that journey begins below the Pacific tectonic plate (one of the rock slabs making up Earth's lithosphere: the crust and upper mantle). Kilauea is centered on this slab, which creeps over a hot spot, or heat plume, deep in the mantle.
All that heat snakes up through the mantle in a process called convection (see Nuts & Bolts, p. 10). Like a blowtorch, the searing heat--reaching 1,400[degrees]C (2,500[degrees]F)--melts the mantle's rocks, turning them into magma. As this hot mix moves upward, some of its trapped gases escape as bubbles. That gives the magma buoyancy (upward force on a floating object)--and a smooth ride from the mantle into the crust.
The ooze collects in a tanklike pocket, or magma chamber, in the crust. Over time, gas bubbles inside the magma build up pressure--so much that the chamber inflates like a balloon. That sometimes triggers a "glowing" eruption.
But this isn't typically a fiery explosion. Kilauea's magma is basalt (volcanic rock containing iron, magnesium, and some silica, or a compound made of silicon and oxygen). That makes it runny, so lots of gases can easily escape before erupting. One deep escapee: carbon dioxide (C[O.sub.2]), the gas that gives soda its fizz. Without much of this gas in the lava, Kilauea's molten material pours out with a splash, instead of with a pop.
Unlike Kilauea, many volcanoes exist at boundaries where two tectonic plates collide. These volcanoes are often fed with magma that mixes with continental plate material, which holds loads of silica. That leads to silica-rich magma that's gluey. The stickiness traps gases in the rising magma. When these volcanoes pop, giant gas bubbles explode from the lava, carrying pillars of ash (fine particles of rock) high into the air.
In Kilauea's runny lava, some trapped gases escape during its lengthy trip--12 kilometers (7 miles)--from its vent to the Pacific Ocean. Edmonds hopes to find changes in its gas content along its journey. But measuring the streams' gases can be tricky: Most lava is tucked beneath crusty chutes called lava tubes. One wrong step onto a weakened tube, and Edmonds could fall into the blistering-hot ooze. So to measure the streams' gases, she looks for skylights, or openings in lava tubes.
The lava's journey ends when it whooshes into the sea, sending a hissing cloud of steam skyward. Edmonds recently found that strong hydrochloric acid (HCl) forms in this shooting plume. "When you walk into the steam, you can feel the acid [burning your skin]," she says.
Kilauea hasn't given up every secret. But being such a tireless eruptor means scientists will have first-row seats for years to come. Says Edmonds: "Kilauea has been erupting since 1983, and it shows no signs of stopping."
Nuts & Bolts
Scientists think that convection currents cause tectonic plates to move. As magma rises through the upper part of the mantle, it heats cooler material. When the hot mix hits Earth's top layers, it spreads out, and pushes cooler material downward. This rising and sinking forms currents which move Earth's plates.
Learn more about amazing volcanoes at the Federal Emergency Management Agency's site: www.fema.gov/kids/ volcano.htm
DID YOU KNOW?
* When Kilauea's lava whooshes into the Pacific Ocean, the lava cools and forms new land along Hawaii's coast. In the past 20 years, Kilauea's lava has created more than 2 square kilometers (0.8 square miles) of coastal land.
* Scientists can estimate the temperature of sizzling lava by looking at its color. For example: White means the molten material is about 1,150[degrees]C (2,100[degrees]F), and bright cherry red is about 700[degrees]C (1,290[degrees]F).
* More than 500 million people live within harm's way of active volcanoes. Research and stage a debate about the pros and cons of volcano-side communities.
SOCIAL STUDIES: According to legend, Pele--the goddess of volcanoes--causes volcanic eruptions in the Hawaiian island chain. Research this Hawaiian myth, and then write an essay summary.
* Grolier search term: volcanoes
* This site is filled with information on topics ranging from the risky life of a volcanologist to volcanoes on other planets. Check out: www.volcanolive.com
* Learn more about the science behind volcanoes at this site: www.pbs.org/wnet/savageearthlvolcanoes/index.html
CHECK FOR UNDERSTANDING
DIRECTIONS: On a separate piece of paper, use details from the article to help you write the following:
1. You're a scientist at the Hawaiian Volcano Observatory. Explain to a tour group the process that leads lava to pour out of Kilauea.
2. You are a volcanologist hiking around Kilauea. Explain to your field assistant why he or she needs to be careful when stepping on what looks like a solid surface.
Island of Fire
Answers will vary but should include the following points:
1. Kilauea sits in the center of the Pacific tectonic plate, which creeps over a hot spot deep in the mantle. The searing heat--reaching 1,400[degrees]C (2,500[degrees]F)--melts the mantle's rocks, turning them into magma. As this hot mix moves upward, it releases some of its trapped gases as bubbles. That gives the magma buoyancy and a smooth ride from the mantle to the crust. The ooze collects in the crust's tanklike pocket, or magma chamber. Over time, gas bubbles inside the magma build up pressure. The chamber inflates like a balloon, which could trigger an eruption. Kilauea has basaltic magma, which allows lots of gases to easily escape before erupting, making the lava runny.
2. Most lava stays tucked beneath crusty chutes called lava tubes. One wrong step onto a weak tube could send you knee-deep into blistering-hot ooze. Also, watch out for skylights, or openings in a lava tube.
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|Title Annotation:||Earth: volcanoes|
|Date:||Nov 22, 2004|
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