Standard Three: Earth S Land and Oceans

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Standard Three: Earth’s Land and Oceans

CURRENT SCIENCE (Vol. 90, No. 8) Dec. 17, 2004, pp. 4+

Copyright © Weekly Reader Corporation. December 17, 2004. All rights reserved. Reprinted with permission.

Super Soaker

By Kirsten Weir

• A giant landslide in the Atlantic will send monster waves crashing into the North American coast. The only question is: When?

Two hundred kilometers off the northwest coast of Africa, waves crash onto the black sandy beaches of La Palma, one of the Canary Islands. Gentle breezes rustle the leaves of the island's almond and banana trees, and dolphins frolic just offshore. To many tourists, La Palma is a tropical paradise. To many scientists, it's a disaster waiting to happen.

Half a century ago, a volcanic eruption shook loose an enormous chunk of the island. Since then the chunk has been sliding slowly toward the sea. Geologists warn that when the chunk eventually breaks off, it will trigger a mammoth wave that will smash into the Canaries, the west coast of Africa, and the east coast of North America. The question isn't if the rock will break, scientists say, but when.

Giant Splash

Colossal waves have struck before. In 1958, Howard Ulrich and his 8-year-old son, Sonny, were boating in Lituya Bay, Alaska, when they heard a thunderous rumbling noise. Suddenly, a wall of water bore down on them. Their boat shot skyward on top of the wave, above the trees along the bank. Somehow, the pair held on and rode the wave down into the bay, unharmed. Several other boaters weren't as lucky.

Scientists later determined that a massive landslide from the cliffs on the opposite side had plunged into the bay, setting off the gigantic splash. The Lituya Bay wave was estimated to be 524 meters (1,720 feet) high--taller than any skyscraper.

(See picture, "La Palma Landslide and Mega-Tsunami.")

(See picture, "Lituya Bay, Alaska: Before and After Landslide.")

After the Lituya Bay incident, scientists realized for the first time that landslides could cause tsunamis. A tsunami is a very large ocean wave that often causes extreme destruction when it strikes land. Underwater earthquakes cause most tsunamis, which usually reach about 10 meters (33 feet) in height. (See Water Wall.) The Lituya Bay wave was 50 times taller. Scientists now call such monster waves mega-tsunamis.

The Lituya Bay wave was somewhat unusual. It blasted the shore and then dissipated almost immediately. When part of an island collapses, however, giant waves rush across the open sea, endangering any landmasses in their paths.

Volcanic Collapse

Scientists have found geologic evidence of island collapses in the past and determined that mega-tsunamis caused by landslides have occurred throughout Earth's history. The biggest known incident happened 2 million years ago in the Pacific Ocean. A chunk of the island of Oahu in Hawaii collapsed to the seafloor. That chunk was 10 times the size of Mount Everest. The landslide must have sent an unimaginably powerful wave shooting across the Pacific Ocean toward the west coast of North America. The most recent mega-tsunami is believed to have occurred in the Indian Ocean, where part of the island of Reunion collapsed 4,000 years ago. The resulting mega-tsunami would have pummeled the west coast of Australia.

Volcanic islands such as Oahu and Reunion are especially prone to devastating landslides. Volcanic islands grow, layer by layer, as lava from repeated eruptions hardens into rock. As the islands grow taller and steeper, ocean waves erode their bases from below. Every few thousand years, a pile of volcanic rock becomes unstable and collapses into the sea. According to volcanic-hazards expert Bill McGuire of University College London, La Palma is the top candidate for the next major collapse.

Half-Mile-High Waves

In 1949, La Raima's Cumbre Vieja volcano erupted, and a huge chunk of land on the western side of the island sank 4 meters (13 feet) into the ocean. Scientists say the half-trillion-ton mass of rock has been slipping slowly downward ever since. Another eruption on Cumbre Vieja could send it collapsing to the seafloor, warns McGuire. The splash would create a mega-tsunami nearly half a mile high.

The massive wave would slam other, nearby Canary Islands. A few hours later, 100-meter (330-foot) waves would batter the west coast of Africa. Traveling at up to 900 kilometers (560 miles) per hour, a mega-tsunami would also shoot westward toward North America. Nine to 12 hours after the landslide, waves up to 50 meters (164 feet) tall would smash into the Caribbean islands and the east coast of the United States and Canada. The wall of water would drown Boston, New York City, Washington, D.C., and Miami.

Will the next big splash hit in two years--or 200? Nobody knows. In any event, the landslide probably can't be prevented, McGuire said.

McGuire believes that governments should collaborate on a project to install more geological sensors on La Palma to better monitor Cumbre Vieja's activity.

No one may be able to hold back the rickety rocks on La Palma, but at least people could be warned when the big one is coming. "The president of the United States has got to make a call at some point," McGuire told The Guardian (London). "When La Palma erupts, what is he going to do?"

Water Wall

All waves, from radio waves to ocean waves, are measured by wavelength, the distance between two consecutive peaks (high points) or troughs (low points). Typical storm waves usually have wavelengths of less than 100 meters (328 feet). Mega-tsunamis, by comparison, have extremely long wavelengths, of up to hundreds of kilometers. (See picture, "Mega-Tsunami: How It Forms.")

Because of their long wavelengths, mega-tsunamis are extremely destructive when they hit a coastline. As the front of the wave nears shore, it begins to slow down. The back of the wave continues to move quickly, pushing against the front and causing it to rear up into a wall of water. Instead of breaking quickly on the shore like a storm wave, the tower of water keeps coming through the entire length of the wave. A single wave can blast across the land for 10 to 15 minutes, drowning everything in its path.

Critical Thinking

• What should governments do to monitor the volcanic activity on La Palma? Discuss.

• How might the loose chunk of rock on La Palma be secured so that it doesn't slide into the ocean and make a big splash?

Internet Links

• National Geographic Xpeditions: Lesson Plans: Finding Monster Waves: www.nationalgeographic.com/xpeditions/lessons/07/g68/wavesmonster.html

Reprinted from
HAWAII VOLCANOES NATIONAL PARK
(U.S. Dept. of the Interior)
1994, n.p.

HAWAII VOLCANOES NATIONAL PARK

Volcanoes are monuments to earth's origin, evidence that its primordial forces are still at work. During a volcanic eruption, we are reminded that our planet is an ever-changing environment whose basic processes are beyond human control. As much as we have altered the face of the earth to suit our needs, we can only stand in awe before the power of an eruption.

Volcanoes are also prodigious land builders--they have created the Hawaiian Island chain. Kilauea and Mauna Loa, two of the world's most active volcanoes, are still adding land to the island of Hawaii. Mauna Loa is the most massive mountain on earth, occupying an area of 10,000 cubic miles. Measured from its base on the seafloor, it rises 30,000 feet, more than a thousand feet higher than Mount Everest. In contrast to the explosive continental volcanoes, the more fluid and less gaseous eruptions of Kilauea and Mauna Loa produce fiery fountains and rivers of molten lava. These flows, added layer upon layer, produced a barren volcanic landscape that served as a foundation for life. Hundreds of species of plants and animals found their way across the vast Pacific on wind, water, and the wings of birds. A few survived, adapted, and prospered during this time of isolation. The arrival of humans, first Polynesians, then Europeans, and the plants and animals they brought with them drastically altered this evolutionary showcase, this grand natural experiment.

Today Hawaii Volcanoes National Park displays the results of 70 million years of volcanism, migration, and evolution-- processes that thrust a bare land from the sea and clothed it with complex and unique ecosystems and a distinct human culture. Created to preserve the natural setting of Kilauea and Mauna Loa, the park is also a refuge for the island's native plants and animals and a link to its human past. Park managers work to protect the resources and promote understanding and appreciation of the park by visitors. Research by scientists at the Hawaiian Volcano Observatory has made Kilauea one of the best understood volcanoes in the world, shedding light on the birth of the Hawaiian Islands and the beginning of planet Earth.

Volcanoes attest to the dynamic nature of the earth. Divided into rigid plates, the outermost layer of the earth drifts slowly over the more plastic mantle beneath. Most volcanic activity occurs along the edge of these plates, forming a "ring of fire." The series of volcanoes that include Washington's Mount Saint Helens, Alaska's Katmai, Japan's Mount Fuji, and the Philippines' Mount Pinatubo define the margins of the Pacific plate.

Why are there volcanoes in Hawaii, which is located in the middle of the Pacific plate? Plumes of magma rise from a "hot spot" deep within the mantle. This fluid rock, charged with gas, melts and pushes its way to the surface, erupting on the ocean floor to create a seamount. After several hundred thousand years and countless eruptions, the volcano rises above sea level to form an island. The volcano continues to grow until movement of the Pacific plate carries the island off the hot spot.

During the last 70 million years the Pacific plate has acted as a conveyor belt, moving the islands northwest off the hot spot at a rate of about 4 inches a year. The park's active volcanoes, Kilauea and Mauna Loa, continue the island-building process that formed the 3,500-mile Emperor Seamount-Hawaiian Island chain.

But they are not the last: To the southeast, Lo'ihi seamount is rising from the ocean floor.

TROUBLE IN PARADISE

The Hawaiian Archipelago was once celebrated as islands of evolution; now they are islands of extinction. The arrival of people changed forever the conditions that fostered the original diversity of life. Forests disappeared as people cleared the land to plant crops and establish communities. Polynesian and other settlers introduced numerous alien plants and animals, some of which thrived in their new home and multiplied. Their impact has been catastrophic: Pigs destroy the understory of tree fern and ohi'a forests. Their muddy wallows provide breeding grounds for mosquitoes that transmit avian malaria and pox to native birds. Mongooses, cats, and rats eat native birds and their eggs. Alien plants such as firetree and banana poka displace vast areas of Hawaiian forests. The onslaught of introduced plants and animals caused the extinction of countless native species and continues to threaten Hawaii's unique life forms.

SAVING AN ECOSYSTEM

Hawaii Volcanoes National Park is an island within an island. It is a shelter for what remains of the once-rich tapestry of Hawaiian life--a tapestry unravelled by alien species. In some areas of the park, natural habitats are damaged beyond recovery. The park concentrates its energies on the most biologically diverse habitats and those that offer the best chance for successful restoration. The immediate strategy is to control or eliminate the most disruptive alien plant and animal pests. Park crews erect fences to keep out feral animals; track and kill feral pigs; and pull out or cut down firetree, banana poka, guava, and ginger. As native plant communities reestablish themselves, populations of Hawaiian honeycreepers, nene, Kamehameha butterflies, and happyface spiders may flourish.

In recognition of its outstanding natural values, Hawaii Volcanoes has been honored as an International Biosphere Reserve and a World Heritage Site. The park continues to mend the fabric and promote the lasting vitality of this remnant of pristine Hawaii.

LIFE COMES TO THE NEW LAND

A few million years ago: A spore from a fern somewhere in southeast Asia is released into the wind and carried by a rising current 8 miles high into the jet stream, where it is borne eastward. Eventually it drifts down and settles on a barren lava field in the middle of the Pacific Ocean. This is one of the ways life came to the Hawaiian Islands.

Insects, seeds, and spiders also reached the islands by riding the air currents, but there were other ways. Migrating or storm-driven birds carried seeds either in their digestive tracts or stuck to their feathers. Pacific Ocean currents transported salt-resistant seeds and rafted insects, plants, and snails on floating debris. Amphibians, reptiles, freshwater fish, and most mammals were unable to cross the vast expanse of ocean--only the monk seal and hoary bat succeeded. Of the millions of organisms that embarked on this chance voyage, very few made it here, and of those that did, few survived.

Over a span of about 70 million years, plants and animals colonized Hawaii at the rate of roughly one every 70,000 years. These species changed gradually with time--they evolved into new forms that were better adapted to island life. In the absence of predators and competitors found in their former homelands, their survival no longer depended on elaborate defense mechanisms. Those qualities that once protected them proved unnecessary and were eventually lost. Contradictory terms describe these new life forms: nettleless nettles, mintless mints, stinkless stink bugs, and flightless birds.