The news isn’t all gloom and doom, however. Scientists working along the southeastern coast of India have found that trees appear to protect seaside settlements from the worst effects of a tsunami.

The December 2004 tsunami knocked down casuarina trees next to the Indian Ocean but left trees farther inland—and the villages behind them—standing.

V. Selvam/Science

When a massive tsunami swept through Asia last winter, it caused massive destruction. Villages surrounded by trees, however, suffered far less damage than did villages without protective forests.

Scientists have long suspected that mangroves (trees that grow in the water along the coast) protect the land nearby. To test this idea, ecologists started collecting data last Dec. 27, the day after the big tsunami struck.

They chose to focus on a 21-kilometer (13-mile) stretch of coast in Cuddalore, India. This stretch was perfect for the study because it was straight and uniform, so waves hit every part of it with about the same amount of force.

Other places were hit harder than Cuddalore, but the 4- to 5-meter (13- to 16-foot) waves that swept into Cuddalore were big enough to destroy two villages. Three other villages survived. The only difference was that the first two had no protective mangroves nearby, while the other three had hundreds of meters of mangroves between them and the ocean.

A few kilometers away, some other villages were surrounded by land-dwelling trees called casuarinas. The trees had been planted after a cyclone 20 years ago. These settlements survived, too, with little damage.

Healthy mangroves also emerged from the tsunami in much better shape than mangroves that had been harmed by people.

The research is important because mangrove forests have been disappearing. People use the wood and destroy the trees to make room for crops and create shrimp farms and fishponds.

Protecting and restoring the world’s coastal forests could be the secret to survival when future tsunamis strike.—E. Sohn

Going Deeper:

Harder, Ben. 2005. Breaking waves: Mangroves shielded parts of coast from tsunami. Science News 168(Oct. 29):276-277. Available at http://www.sciencenews.org/articles/20051029/fob3.asp .

You can learn more about mangrove trees at www.epa.gov/owow/wetlands/types/mangrove.html (U.S. Environmental Protection Agency) and www.naturia.per.sg/buloh/plants/mangrove_trees.htm (Chek Jawa, Singapore).

Sohn, Emily. 2005. Unnatural disasters. Science News for Kids (Sept. 21). Available at http://www.sciencenewsforkids.org/articles/20050921/Feature1.asp .

______. 2005. Saving wetlands. Science News for Kids (April 6). Available at http://www.sciencenewsforkids.org/articles/20050406/Feature1.asp .

______. 2005. Wave of destruction. Science News for Kids (Jan. 19). Available at http://www.sciencenewsforkids.org/articles/20050119/Feature1.asp .

______. 2005. Digging into a tsunami disaster. Science News for Kids (Jan. 12). Available at http://www.sciencenewsforkids.org/articles/20050112/Note2.asp .

______. 2004. Recipe for a hurricane. Science News for Kids (Sept. 29). Available at http://www.sciencenewsforkids.org/articles/20040929/Feature1.asp .

______. 2004. An ocean view’s downside. Science News for Kids (March 31). Available at http://www.sciencenewsforkids.org/articles/20040331/Note2.asp .

This satellite image shows Hurricane Katrina over the Gulf of Mexico before it slammed into the coast of southeastern United States on Aug. 29.

NASA

Hundreds of thousands of people fled before the storm hit, but many others were left stranded on rooftops, floating on makeshift rafts, and separated from their families. Some went without food or water for days. Hospitals lost power. Telephone systems failed. Hundreds of people died.

Hurricane Katrina was one of the deadliest and most costly natural disasters in living memory. But how “natural” was it?

“The phrase ‘natural disaster’ misses the point,” says geologist Jeffrey Mount of the University of California, Davis. “This is only a disaster because people got in the way. Hurricanes are a natural process.”

In New Orleans after Hurricane Katrina, floodwaters swamped houses.

Photo by Liz Roll, FEMA

In this latest encounter between people and nature, nature seems to have won. Some analyses suggest, however, that human actions made the destruction caused by Hurricane Katrina worse than it might have been. There were also things that people could have done beforehand to lessen the hurricane’s impact.

In fact, as horrifying as Katrina was, its effects weren’t a complete surprise. For years, scientists and engineers had been warning that just such a storm could flood New Orleans and wipe out coastal communities.

Natural disasters

Five years ago, in his book Acts of God: The Unnatural History of Natural Disaster in America, historian Ted Steinberg reported the good news: In modern times, fewer people are dying in natural disasters, thanks to improved systems of communication, refined methods of tracking weather, and better evacuation plans.

New Orleans has suffered a number of floods over the past 100 years. This photo was taken in 1965, when Hurricane Betsy caused the flooding of 164,000 homes in the city.

R. Vetter, American Red Cross, NOAA Photo Library

Steinberg described a major hurricane that hit Florida in 1928, killing 2,000 people, and a massive earthquake in San Francisco that took thousands of lives in 1906, among other long-ago disasters.

“But I said at that point in the book that if there were any place where it was possible to see a return to the mass death we saw in 1928 and 1906, it’s New Orleans,” Steinberg says. “Anybody, going back 10 or 15 years, could see this was a disaster just waiting to happen.” Steinberg is a professor at Case Western Reserve University in Cleveland, Ohio.

New Orleans sits on the Mississippi River delta, where the river dumps into the Gulf of Mexico. For hundreds of years, the river deposited silt throughout the delta. Flooding was a regular occurrence.

Surrounding marshes were dense, nearby islands were in good shape, and both absorbed the impact of hurricanes that regularly hit the area during the summer (see “Saving Wetlands”).

The levees protecting New Orleans have grown higher and wider over the years. This diagram shows the cross-section of a typical levee at various times, from 1717 until 1973. How have its size and shape changed?

U.S. Army Corps of Engineers

Then, starting in the 1880s, engineers built levees, or wall-like barriers, around New Orleans to protect it from floods and hurricanes. The levees were designed to keep water out of the city in the face of storm surges from hurricanes, which raise the water level, or of flooding by the Mississippi River. At various times in the past 100 years, these levees were extended and built higher.

Sinking land

Since the levees were built, the city has not had regular flooding. Silt no longer builds up. As a result, the ground under New Orleans has been sinking for years. It’s the only city in the United States that sits largely below sea level. It’s somewhat like a bowl surrounded by water.

Over the years, the construction of roads, homes, and buildings has caused erosion of the coast and offshore islands. The waters of the Gulf of Mexico are much closer to the city than they had been in the past.

“Now, when hurricanes come,” Mount says, “the natural shock absorber of the delta is gone, increasing the impact of storm surges.”

The Chandeleur Islands are about 100 kilometers east of New Orleans. The image on the left was taken in July 2001. The image on the right was taken on Aug. 31, 2005, 2 days after Hurricane Katrina. High water created by the storm surge and large waves sub

U.S. Geological Survey

Levees can’t take all the pressure. Over time, as water piles up, it works its way through the structures and erodes them from the inside out. Then, with pressure from fast-moving water during major storms such as Katrina, the levees collapse.

“Most levee engineers will tell you that there are two kinds of levees,” Mount says. “Those that have failed, and those that will fail.”

Theoretically, taller, stronger levees could have saved New Orleans, Mount says. But at some point, it becomes too expensive to build structures strong enough for all possible situations.

Levees can also be dangerous, Steinberg says, because they make residents feel safer than they actually are. The city grows, and that puts even more people at risk.

Prevention

Scientists are now looking for ways to prevent similar disasters from happening again. Some engineers want to deflect floods instead of just blocking them. Other researchers are designing improved storm-resistant buildings and roads. Still others are trying to better predict where hurricanes will go and how hard they’ll hit (see “Recipe for a Hurricane”).

These satellite images show the damage that New Orleans suffered as a result of Hurricane Katrina. The lower image shows New Orleans and the surrounding area on Aug. 27, 2005, before Hurricane Katrina struck. The upper image shows the city on the morning

NASA

In the long run, restoring the environment of the Mississippi River delta will be essential. People will also need to start respecting nature, instead of thinking they can outsmart it. After all, Mount says, animals managed to survive the flooding cycles of the delta for thousands of years.

“But modern humans, with their big buildings, roads, power lines, and houses, are not as well adapted,” he says. “Many of the things we do, such as constructing levees and destroying marshes, make these ‘unnatural disasters’ worse.”

Recognizing the role that people play in natural disasters is an important way to overcome our fear of them, Steinberg says. “You don’t have to see these events as natural disasters beyond our control.”

If we took more seriously what can happen in natural disasters, he says, “we could prevent them from being quite as devastating in the future.”

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Word Find: Hurricane Katrina

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Not totally flooded by water, but not completely dry either, these in-between places rank among the richest ecosystems on Earth. Marshes, mangroves, bogs, swamps, bayous, prairie potholes, and other wetlands often have more plant and animal life than any lakes, rivers, grasslands, forests, or hillsides nearby.

A bayou, like this one in Louisiana, serves as a home for many species, ranging from bald cypress trees to a host of wetland-dependent animals, including ospreys, herons, and egrets, along with alligators and beavers.

U.S. Fish and Wildlife Service

Baby fish and shellfish thrive in the protected waters of shallow estuaries, where rivers meet the sea. Many types of migratory birds spend their winters in marshes or stop there to rest during their travels. Wetlands are full of salamanders, frogs, turtles, snakes, and alligators, as well as sea grasses and other specialized plants.

“They’re really beautiful environments,” says Denise Reed of the University of New Orleans. She studies landforms and the processes that made them.

Reed is determined to get people to care about wetlands—and not just because they’re beautiful.

Wetlands also help preserve water quality. They protect land from getting battered by storms. And they fuel billions of dollars worth of recreation, fisheries, and other industries.

Disappearing marshes

Unfortunately, the world’s wetlands are disappearing.

In the last few hundred years, more than half of the wetlands in the United States (excluding Alaska and Hawaii) have vanished, according to the National Wetlands Research Center. The center is part of the U.S. Geological Survey.

These wetlands in the Grand Cote National Wildlife Refuge in Louisiana include a crawfish pond bordered by smartweed. Such a mix of habitat supports a wide variety of species. Northern pintail ducks spend their winters here.

U.S. Fish and Wildlife Service

Louisiana’s wetlands, in particular, are in need of help. Even though it’s a fairly small state, Louisiana holds 30 percent of the nation’s coastal marshes along its meandering coastline, especially where the Mississippi River drains into the Gulf of Mexico.

Yet, of all marshes that have disappeared in the U.S., 90 percent were in Louisiana, according to an organization known as America’s Wetland. This group is dedicated to saving the Louisiana coast.

During the 20th century, 1.2 million acres of land were lost along the state’s coast. Between 1990 and 2000, alone, the equivalent of a football field-sized area of wetland disappeared every 38 minutes.

These are more than just numbers. As wetlands vanish, fish and migrating birds lose critical habitat. Some of these species are already endangered.

Human lives are at stake, too. More than half of Louisiana’s population lives along the water, and many of these people rely on fishing and shipping to survive.

“I think it’s one of the biggest environmental issues there is,” says Garret Graves. Graves grew up in Louisiana but now lives in Washington, D.C., where he works with Louisiana politicians to create laws that will help restore the area.

Vanishing mystery

Why Louisiana’s wetlands have been disappearing has long puzzled researchers. Now, after several decades of research, some of the reasons are becoming clearer.

The culprit isn’t normal erosion, which happens when waves gnaw away at the land. In this case, the marshes are falling apart from the inside out.

Walking through the wetlands used to be like slogging through a squishy field of wet hay. Now, invisible holes lie all over the place. People walking around in the marshes today can fall up to their knees in water without warning, Reed says. “It’s like a Swiss cheese effect.”

Sinking marshes in Louisiana create an intricate pattern where water and land meet.

U.S. Fish and Wildlife Service

Why this is happening is a complicated question. There seem to be a number of factors involved, Reed says.

One is the Mississippi River. Water used to come down the Mississippi full of sediment and dirt, which piled up in the marshes and kept them sturdy. Flooding was part of the normal course of things, and the process helped distribute sediment.

Then, in the mid-1900s, oil companies discovered a huge quantity of oil and gas just off the coast of Louisiana. They built extensive networks of canals, called levees, to control the flow of the river, providing better access to Earth’s natural resources. These efforts ended up changing the flooding cycle. Sediment couldn’t spread through the marshes, and the wetlands grew weaker.

Next came development, which filled in marshes to build parking lots, shopping centers, and houses on top of the wetlands.

Large rat-like animals called nutrias are also causing problems. In a healthy marsh, the animals simply graze year after year without causing too much damage. When a marsh is stressed out, though, nutrias eat away at them.

Imported animals known as nutrias may be contributing to the decline of Louisiana’s marshes.

John and Karen Hollingsworth, U.S. Fish and Wildlife Service

All these stresses add up. “There’s no one factor you can point to and say, ‘This is the culprit. Here’s the smoking gun,’” Reed says. “There are many things going on that cause stress to wetlands. The wetlands could take any one or two of them. Once you get three or four on top of each other, though, the marsh just can’t hang on anymore.”

Trapping sediment

Now that scientists have a good idea of what’s happening to the wetlands, the next challenge is to figure out how to fix the problem, Reed says.

In her research, she’s trying to understand why some marshes have managed to survive, even as so many others have vanished.

“How do they keep their heads above water?” she asks. “Where do they get their sediment from? How do they build themselves up when the land is subsiding?”

For about 10 years, Reed has been scattering sediment traps made out of filter paper on the surface of marshes in Louisiana. She attaches the traps to the ground with aluminum wire. Then, she checks them every 2 weeks.

Traps made out of filter paper capture sediment in marshes.

Denise Reed

The traps are clean when Reed puts them in and muddy when she comes back. With the data she collects, she can track when and how much sediment builds up over short periods of time and over the years. She also takes samples of the soil to study how plant roots might help hold a wetland together.

Among her results, Reed has found that hurricanes actually deposit a lot of sediment in salt-water marshes. “Everyone thinks ‘Hurricanes, oh my God, they’re so bad,’” Reed says. “It is bad for people. For marshes, it keeps them going.”

Political action

Even as research continues to help scientists understand what wetlands need, understanding can go only so far, Graves says. The only way to truly reverse wetland destruction, he argues, is through politics.

It would cost $15 billion to cut slits in the earth and restore natural sediment flow patterns along the Louisiana coast, Graves says. That’s money the state doesn’t have. He wants the U.S. Congress to create new laws that would give Louisiana a big chunk of the profits that come from the oil and gas obtained off its coast.

The state could then put this money toward reconstructing the environment. Right now, the U.S. government officially owns these resources.

Despite 8 years of work on the issue, Graves hasn’t seen much progress. His passion has grown with his frustration.

Student Cathy Cebul of Wooster, Ohio, examines shellfish specimens that she gathered during a recent JASON Expedition to explore Louisiana wetlands.

Copyright © 2005 Jason Foundation/Daniel J. Splaine

Scientists and politicians aren’t the only ones who have grown passionate about Louisiana’s wetlands. Kids have started to get involved, too.

Earlier this year, an educational program called the JASON Expedition gave middle school students a close look at wetland research in Louisiana.

Most of the students participated in the expedition through the Internet and live satellite broadcasts, but some actually got to dig in the mud and explore the science with their own hands.

By the end of the weeklong program, the most popular question from kids, Reed says, was, “What can I do?”

The answer, she says, depends on where you’re from. You may not live in Louisiana or even near a coast. Chances are, though, Louisiana’s problems hit closer to home than you might think.

Nearby wetlands

“Almost everyone has a wetlands nearby,” Reed says. If you’re looking for a science fair project idea, she suggests, go find out about your local wetlands.

“As you learn and understand it better, you might then see things you can do in terms of cleaning it up,” she says. “Learning is part of doing something. Try to understand how it works.”

Students Rosalind Fennell (left) and Ambika Nath (right) and teacher Suzanne Ciccarelli (center) survey plant species in the swamp at Jean Lafitte National Historic Park, Barataria Preserve in Marrero, La., during a recent JASON Expedition to Louisiana wetlands.

Copyright © 2005 Jason Foundation/Daniel J. Splaine

Find out what sustains the wetlands in your area, why they’re there, and what they give to your community. Think about the water that drains into them, where it comes from, and what you can do to keep it clean.

Using less water is something everyone can do, Reed says. This helps keep rivers and lakes full, which reduces the strain on wetlands. Paying attention to what goes down storm drains can protect them, too.

If you’re really inspired, you can study to become a wetland ecologist. Wetlands are fascinating systems to study, Reed says, because they’re always changing.

When the fish are jumping, the birds singing, and the marshes green, wetlandscapes can be beautiful. Even better, they’re full of mud, and studying them requires hands-on slogging through squishy dirt and mud, Reed says. “Who doesn’t like getting dirty?”

Whatever we do, it’s important to do it soon, she adds. “This system could be in radically different shape in 10 years if we get moving,” she says. “If we stay this way, it’s still going to be in radically different shape, but in the wrong direction.”

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Word Find: Wetlands