EARTH SCIENCE geology, the environment, and the universe 2008 (32)

891 George Steinmetz/National Geographic Image Collection... NG Maps/National Geographic Image Collection... pla-State of Rock Where the Elements Reign` ● RIGHT: Blasted by wind, bro-k

e X peditions!

Swim the Okavango

Explore the African

Landscape

Dig for Dinosaurs

crocodiles in the Okavango delta? Or fly in a bush plane over the African continent? Or dig for dinosaurs in

China? The National Geographic Expeditions allow

you to share in the excitement and adventures of

explorers, scientists, and environmentalists as they

venture into the unknown Each Expedition takes

you on a journey that enriches your learning about

our dynamic planet

890

892 Tracing the Human Footprint Use with Chapter 2

For more information on these Expeditions, visit glencoe.com You can also link to original National Geographic articles that cover these topics and more.

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George Steinmetz/National Geographic Image Collection

NG Maps/National Geographic Image Collection

From a low-flying plane is how

J Michael Fay sees the land on a mild December morning, as an heirloom Cessna 182 carrying him and three others approaches the Aïr Massif, a vast range of highlands standing up from the Sahara The Cessna is painted scarlet and specially equipped for collecting data The plane looks like a toy, or an enameled piđata, but it bears serious purposes, not candy With a young Austrian pilot named Mario Scherer at the controls, and Fay in the right seat amid a rat’s nest

of custom-rigged digital hardware and cables, it caresses the topography, circling here, dipping a wing there, rising nervily through high notches to put peaks close at eye level on each side Mounted in its right door is a high-resolution digital cam- era that automatically, every 20 seconds, takes a vertical shot of the ground The photos, each tagged with Global Positioning Satellite (GPS) data registering exact time, latitude, longitude, and altitude, are uploaded into a computer on Fay’s lap, through which he can add notes A similar computer, scrolling out a map along the plane’s flight line, rests under his left elbow Fay’s attention flicks constantly, tirelessly, between the computer screens and the terrain passing below.

Tracing the Human

Footprint

Africa by Air

● ABOVE: Biologist J Michael Fay

catches some sleep after eight hours

in the air On board this and another

Cessna, Fay, pilots, photographers,

and others risk their lives to map

humanity’s impact on tropical

for-ests, savannas, and deserts Along

the way on this “Megaflyover” they

struggle against malaria,

sand-storms, and brushfires and try to

keep the planes, computers, digital

cameras, and GPS systems running

● LEFT: The map of Africa shows

the zig-zag route taken by Michael

Fay during a joint project—the

Human Footprint—of the Wildlife

Conservation Society (WCS) and the

National Geographic Society.

● ABOVE: The Namib Desert is just one of the 104 terrestrial

ecoregions identified in Africa Among Earth’s driest places—and

perhaps the oldest desert—it boasts orange sand dunes made

sharp and steep by the blowing wind

The Realities of Land Use

Today is our tenth day of survey flying in Niger, and the 187th day since Fay and his chief pilot, Peter Ragg, departed from an airfield in South Africa Fay’s aerial enterprise is closely linked with

an ambitious initiative of the Wildlife Conservation Society — the Human Footprint project That proj-ect involves a program of multidimensional map-ping to show gradients of wildness and human impacts around the world

Fay himself, a restless individualist with a prisingly good nose for politics, wants nothing less than to change the way the world perceives and uses ecosystems and natural resources — starting with perceptions in Wash ing ton, D.C The ultimate goal of his Africa Mega flyover, he says, is to con-vince “the powers that be, in particular the U.S

sur-Congress,” that integrating natural resource agement into American foreign policy is “a very, very smart thing to do And a good investment.”

man-Wherever humans live at high population ties, making unsustainable demands on natural sys-tems, he notes, you eventually see ecological breakdown Unmet needs and tensions lead toward conflict A pilot himself, he recognized the value of low-altitude flying to illuminate the realities of land use

densi-● BELOW: The Ituri Forest in the Congo is a vastly different type of

ecoregion from the Namib Desert in terms of the amount of rainfall,

types of vegetation, and animal life.

(t)George Steinmetz/National Geographic Image Collection ,(b)George Steinmetz/National Geographic Image Collection

● ABOVE: Lake Natron straddles Tanzania and Kenya Along Kenya’s section

of the lake, microorganisms living in the water’s salty crust create a palate of pink Pigments in the organisms cause the feathers of the flamingos that depend on the lake for food to turn pink.

A bush plane shows you patterns

you’ll never perceive from the ground It

allows flexibly targeted coverage (“Let’s

circle that spot again”) and the capture of

fine details you can’t get from a satellite

Africa, the continent he knows and loves

best after 25 years of working there, was

the logical place

What Is Africa?

Of course Africa isn’t really a place;

it’s a million places Nowadays it

encom-passes 47 countries (not counting

Madagascar and other islands) with a

total population of 900 million humans

It can also be parsed into 104 terrestrial

ecoregions, each unique in its physical

and climatic features Each one harbors

a distinct plant and animal community

Ecoregions in many cases transcend

national boundaries Within or near all

these ecoregions live people whose most

elemental struggles and aspirations

tran-scend ecological boundaries as well as

national ones Africans want better and

fuller employment They want food

security and education for their children They

want good governance, free of oppression and

cor-ruption They want fair, sensible arrangements for

the management of wild landscapes and natural

resources — arrangements chosen and controlled by

Africans They want peace

Along with the human struggles come human

impacts Although some areas of Africa are less

heavily inhabited than they might be, others are

overburdened, eroded and blighted by the presence

and demands of too many people Because the

African landmass is so large, climate change may

affect its interior regions by bringing considerably

higher temperatures and worse droughts and

floods This contributes to increased desertification

and new patterns of disease Poaching wildlife, both

for subsistence and commercially, is an old problem

but still serious Timber harvesting, even when

done selectively, often brings workers who empty

a forest of its fauna for bush meat

None of these concerns is unique to Africa

But Africa particularly deserves special attention

Africa’s glories and successes deserve special tion, too African peoples produce magnificent art, graceful cultures, terrific music, great works of the mind, and astonishing acts of political and moral courage

atten-Documenting Ecological Dimensions

Fay’s intent is to document the ecological sions of that variousness His conceptual starting point was the World Wildlife Fund map of 104 African ecoregions and the Human Footprint proj-ect, conceived by Eric W Sanderson and a team of colleagues at the WCS and Columbia University

dimen-Sanderson’s group used nine different geographic data sets (measuring factors such as road density, railways, population density, nighttime lighting) to represent the weight of human influence all over the planet, including Africa

● ABOVE: A herd of buffalo is seen wallowing in the muddy swamps

of the Zambezi Delta in Mozambique Protection efforts there seem

to have buffalo populations increasing.

896

● ABOVE: View of an area near the Mahajamba River on

Madagascar reveals a rocky terrain Madagascar is considered a hot

spot for conservation because its unique flora and fauna are found

nowhere else and there are tremendous population and resource

pressures on the land.

Fay wanted to cover as many of the 104 regions

as time, budget, and politics would allow Then he would present an enormous body of data — between what is possible to what is actually happening — to decision-makers and say: Here’s some information that might be relevant to your resources-and-security planning

Fay recruited Ragg, an experienced bush pilot (and, in an earlier life, a successful optometrist in Austria), who offered his flying skills and the use of his two vintage airplanes, one for primary data gathering, one for support Ragg in turn enlisted his fellow Austrian, Mario Scherer, who had found African bush flying a lively change from his recent work as a war-crimes investigator in Kosovo Fay drummed up support from various sources—the Human Footprint lab at WCS, the WILD

Foundation, the Bateleurs (an Africa-based zation of bush pilots volunteering for conserva-tion), and, as chief financial sponsor, the National Geographic Society

organi-Beginning the Megaflyover

The first takeoff was on June 8, 2004, from Swartkop Air Force Base near Pretoria Soon after,— OK, it was five minutes — Fay’s network of digital gizmos suffered an outage The camera quit, the computers went to battery power, and he sniffed a hint of electrical fire Oh well, he thought, better a data-system meltdown than full-on engine failure within sight of the runway He re-rigged

Hopping his way across southern Africa and then northward on a chain of one-day flights, Fay arranged collaborations wherever possible He assisted local conservationists, field scientists, or national agencies with their aerial-survey needs as well as adding data to his own comprehensive trove Wherever he went, Fay tried to complement the aerial data-gathering with contacts, conversa-tions, and observations on the ground

Many computer crashes, camera shutdowns, and other minor problems have followed that first glitch above Swartkop Most were easily repaired There have also been a few dire aviation scares, caused by high winds, drastic loss of oil pressure, and other forms of mischance

By the time I [David Quammen] met

them in Niger, Fay and his pilots had

flown 600 hours, crisscrossing 16

coun-tries, usually at about 150 meters (500

feet) above the ground One of the

Cessnas had gotten a new engine Both

planes needed maintenance

Theme of Absence

From the air over Niger we enjoyed

some notable sights A pair of addaxes

skittered like sand crabs along a

linear dune Seven Barbary

sheep galloped up sausage-like

towers of dark sandstone along

the Djado Plateau Camels

stood stuporous and serene in

the middle of nowhere Near

one village we gawked down at

a cluster of saltmaking pits

Each pit, a nice disk, variously

sized, shone azure or turquoise

or coppery green from the

mineral solutions of their

indi-vidual sumps — all together a

necklace of bright-colored

jewels

Mostly what we observed

and recorded, though, were

variations on a theme of absence Some days we

flew a 650-kilometer (400-mile) loop without

glimpsing a single animal, and dozens of miles

without spotting so much as a plant Even absence

is a form of data Niger is a country desolated by

recent human-caused losses The addax is nearly

extinct here, for instance, and the Barbary sheep,

and the desert cheetah Their disappearance from

remote habitat areas may correlate with the

pres-ence of four-by-four tracks, indicating unimpeded

access by poachers Such tracks show clearly from

150 meters (500 feet) up

Another sight came into view: a large green oval

It was a pond, evidently spring-fed from beneath

the sands Water? Fay peered down for a moment,

having noticed something, tapped a note into his

computer: “no animal tracks.” It hadn’t struck me,

but of course: A water hole out here should attract gazelles and other mammals from many miles around — attract them, that is, if any exist He tapped again: “4x4.” Meaning, tire marks An absence of animal sign, a presence of human sign

Cause and effect? Anyway, data The challenge for Fay is that he must deliver meaning from the mountainous pile of facts and photographs he has collected

● ABOVE: An old abandoned town north of

Dirkou, Niger, is built of blocks of salt The houses without roofs reveal room after room, some only a few feet square Newer towns are built of mud brick and have satellite dishes and telephones.

● LEFT: Casablanca, Morocco, is an enormous

place, with miles and miles of buildings Water availability is evident from the green vegetation.

e X peditions activityConsider the kind of variation there must

be to have 104 distinct ecoregions in Africa Verbally illustrate an ecoregion by listing and describing some of its factors.

Frans Lanting/National Geographic Image Collection

Bizarre Is that the right word for the Colorado Plateau, this thirsty sprawl of gaudy-hued stone festooned with such names

as Hell Roaring Canyon, Scorpion Gulch, and Horsethief Point?

Edward Abbey began his classic Desert Solitaire with the simple

“This is the most beautiful place on earth.” Fiery rock can do that

to a person Others trying to understand the attraction of the teau country apply adjectives like “amazing” and “awesome.” In truth, a single adjective may not suffice All the same, as I [Mike Edwards] fly over the plateau on a May morning, looking down on whalebacks of slickrock, on crashing waves of rock, on minarets and pyramids of rock hewn by water and wind—how could any word fit better than “bizarre”?

pla-State of Rock

Where the Elements Reign`

● RIGHT: Blasted by wind,

bro-ken by water, the Colorado

Plateau spreads across 336,700

square kilometers (130,000

square miles) of Arizona, New

Mexico, Utah, and Colorado This

arid expanse, best seen by air,

has been called useless by some,

a landscape that conspires

against human settlement For

others it’s nature’s grandest

work in progress.

● LEFT: Hoodoos are columns of

rock in fantastic shapes that are

found in western North America

These appear in Utah’s Bryce

Canyon National Park.

NG Maps/National Geographic Image Collection

Water’s Tattoo

Desert this is, but water’s tattoo is everywhere

Spidery little arroyos coalesce into bigger arroyos that plunge into the still deeper groove of a river, maybe into the thousand-foot-deep canyon of the Escalante, a scalpel-cut in red rock, so narrow that the stream and its fringe of willows and tamarisks are invisible unless you’re dead-on overhead

Most of the collected runoff, if it hasn’t vaporized

or died in a mudflat, swells the Colorado River By the time the river courses into Arizona and roars into the plateau country’s most dazzling feature, the Grand Canyon, it is plowing a furrow more than a mile deep Pretty impressive digging, this, consider-ing that the precipitation in parts of the plateau averages only six inches a year

Water was also present at the creation, in far greater abundance Tens of millions of years ago, seas, swamps, and rivers deposited dozens of layers

of rock: limestones, mudstones, shales, many dened by traces of iron In those eons the plateau country was flat and much lower than its heights today, which are typically 1,524 meters (5,000 feet) above sea level Winds also contributed raw mate-rial, the makings of sandstone layers hundreds of feet thick The whole shebang was thrust upward

red-by forces within the Earth

● TOP LEFT: Dawn casts a Martian glow over the Buttes of the

Cross in Glen Canyon National Recreation Area Miners once scoured

this backcountry for uranium Today the mines are silent

● TOP RIGHT: A water-carved fist jabs across a canyon in Utah’s

Capitol Reef National Park.

● ABOVE: Factory Butte looms over unproductive curves and folds

of shale, salty sediments deposited by an ancient sea.

● ABOVE: A bathtub ring of bleached rock—a sign of severe drought—lines Lake

Powell, the country’s second largest human-made lake and canteen for much of the Southwest Long years of drought and demand from distant cities have depleted the lake’s reserves The years 2000–2005 are the driest five years in a century.

Colliding tectonic plates tilted

and bent layers like cardboard

Everywhere then as now, water

attacked the soft stones, carving

canyons That’s Plateau Geology

101, slightly abbreviated

Powell’s

Hundred-Day Journey

Winging 762 meters (2,500

feet) over this rockscape, I feel a

tenuous kinship with John

Wesley Powell On his scary

hun-dred-day journey down the

Green and Colorado Rivers in

1869, that indefatigable

adven-turer-scientist surmounted cliff

tops to reconnoiter the uncharted

territory he had penetrated Of

course, I’m riding shotgun in a

Cessna while Powell had to pull

himself up one-armed from a

riv-erine chasm to a lookout; he lost

his right arm at Shiloh in the

Civil War But we gaped at the

same sights “The landscape

everywhere ,” he wrote, “is of

rock—cliffs of rock, tables of

rock, plateaus of rock, crags of

rock—ten thousand strangely

carved forms.”

Clearly Powell was awed by the

fantastical convolutions of this

land He became the chief

exposi-tor of the “plateau province,” as

he called it, documenting not

only the geology but also the

ways and lineages of its Indians,

meanwhile campaigning for

sen-sible husbanding of the water

● RIGHT MIDDLE: Swelling beneath Arizona’s

Coyote Buttes, sandstone waves evoke white

water

● RIGHT BOTTOM: This view of Earth’s outer

layers shows fractures in sandstone that form

car-size blisters.

(t)Adriel Heisey/National Geographic Image Collection, (c)Frans Lanting/National Geographic Image Collection , (b)Frans Lanting/National Geographic Image Collection

● ABOVE: Photographer Adriel Heisey found a paradise of form as he soared over bands of

shale and sandstone “Everywhere I turned,” he says, “there were geometric patterns that

defied my ability to comprehend.”

● BELOW: Sunlight pours over Jacobs Chair, a Utah butte named for a cattleman who

drowned fording a storm-swollen creek nearby In the late 1800s Mormon pioneers left

a trail of names as they hacked a wagon route across southern Utah during the grueling

Hole-in-the-Rock expedition.

902

Protecting The Landscape

Powell hadn’t glimpsed some

of the craziest rock shapes—the pinnacle-like hoodoos of Bryce Canyon or the vaulting spans of Arches, canonized by Edward Abbey Bryce and Arches are two

of the roughly 30 parks and other national preserves that make the heart of the province one of the nation’s most protected regions

It isn’t perfect protection; mentalists decry its insufficiencies while locals, ingrained with the Westerner’s mistrust of bureau-cracy, grumble about overkill In the largest unit, the 1.9-million-acre national monument Grand Staircase–Escalante, created only in

environ-1996, off-road vehicles plow tracks that won’t disappear for decades

On the other hand many mining claims have been relinquished or bought out by those devious Feds, and no new claims are permitted

And while allowing multiple uses, including ranching (yes, there’s a little grass here and there), the Bureau of Land Management is charged with superintending the monument to protect its attributes

Protecting Earth’s History

Gaudy vistas are only one of those attributes The plateau is a time machine nonpareil, holding who knows what secrets When the rocks at the bottom of the Grand Canyon are counted in, the swath

of Earth’s history exposed by water’s relentless gouging of the plateau is reckoned by geologists to reach back 1.7 billion years, more than a third of Earth’s existence

(t)Adriel Heisey/National Geographic Image Collection, (b)Adriel Heisey/National Geographic Image Collection

e X peditions activityResearch the status of and plans for conservation

on the Colorado Plateau Discuss whether changes

in weather have affected the status and plans and how the plans may affect people who depend on the Colorado River for their main source of water.

One afternoon, puffing along behind Alan Titus,

a BLM paleontologist, I dropped back a mere 75

million years or so Titus assured me we were

tramping through a swamp where ferns and

mag-nolias had flourished, although it looked awfully

like a forest of stunted piñons and junipers “The

whistles and shrieks you hear are not birds,” Titus

said, coaxing my imagination into play “They’re

dinosaurs.” Soon he had me seeing huge crocodiles

and snakes sloshing lazily in warm pools And then,

guiding me to a row of dark, roundish objects

half-buried in the soil, Titus said: “You’re looking at the

remains of an animal that’s been extinct for 65

mil-lion years or more”—the fossilized vertebrae of a

duck-billed dinosaur that lived in the Cretaceous

period Titus says this specimen was 25 feet long

“I’m waiting for that big tyrannosaur,” he said “I want to find one before I retire.”

On another afternoon I climbed to a high cliff ’s edge The setting sun infused the rocky layers vault-ing away to the horizon with a crimson incandes-cence—the kind of glow, surely, that compelled Edward Abbey to pronounce these rocks beautiful

A hot, dry wind came up, gusting stronger and stronger, and as it assaulted the cliff faces it whined and screamed Sounded just like dinosaur shrieks

● ABOVE: Standing tall against the cold, Castle Rock (on the right), and other buttes bear a dusting of snow

in Monument Valley With each season the elements shape the plateau anew, shattering canyon walls and cliff

faces, chiseling subtle changes into the enduring symbols of the West.

David Doubilet/National Geographic Image Collection

The Miracle Is This: Under cloudless skies at the driest time of Botswana’s year, when rain is both a fading memory and a distant promise, a flood comes to the Okavango Delta

Generated by rainfall 804 kilometers (500 miles) and two countries away in the highlands of Angola, the flood wave snakes down the Okavango River and spreads across the delta, swelling its lagoons and channels and spilling outward to inundate its floodplains In a land withered by drought, this gift of water is like unction, and all nature responds to it.

“My surface gives you life Below is death.”

The delta’s deepest, most diverse underwater habitats lie in the Panhandle The flood peaks here in April, raising the level of the Okavango River by six feet In May the level has started to drop Sediment borne on the flood wave has settled, and the water in Ncamasere channel,

an offshoot of the main river midway down the Panhandle, becomes clean and clear And deadly The waters of the delta are full of crocodiles

The Bayei people, one of several Okavango tribes, say as much in a poem they teach their children: “I am the river My surface gives you life Below

is death.” For photographer David Doubilet and me [Kennedy Warne], going below the surface was an essential part of our work

Okavango

Africa’s Miracle Delta

● RIGHT: The miracle happens in

slow motion, for this part of

south-ern Africa is so flat (a gradient of

about a hundredth degree) that the

floodwaters take three months to

reach the delta and four more to

tra-verse its 240-kilometer (150-mile)

length Yet by the time its force is

spent, the flood has increased the

Okavango’s wetland area by two or

three times, creating an oasis up to

half the size of Lake Erie It is one of

the largest inland deltas on Earth

From space the delta looks like the

footprint of a bird Water flows into

the system through the leg, called

the Panhandle, a strip of land 96

kilometers (60 miles) long and 14

kilometers (9 miles) wide along

which the Okavango River meanders

in lazy loops Forward-pointing toes

channel water through the delta.

● LEFT: Suspended in an ethereal

realm of water lilies, and light, a

river Bushman, pole in hand, peers

into the emerald forest of

Botswana’s Okavango River As if by

magic it ebbs and flows with

sea-sonal floods before vanishing in the

Kalahari Desert The result: an oasis

for wild things above and below the

surface.

We wanted to see the delta as few had dared to

see it before—a croc’s-eye view People in passing

boats, noticing our wet suits and scuba gear, didn’t

hesitate to give their opinion on croc-watching:

you’re out of your minds Perhaps we were, but it

was winter, and we reasoned that because

croco-diles are reptiles, their metabolism would be

sluggish

The larger crocodiles spent much of the day

basking on the riverbanks in well-used haul-outs,

usually with chutes down which they slid into the

water if disturbed In the cool of the night the

warmth-loving crocs came to life for the hunt,

floating at the water’s edge Their eyes gleamed

blood-red in our spotlight as we motored up the

channel Although Nile crocodiles are one of only a

handful of predators that actively hunt humans, I

figured that if I initiated an encounter, thus denying

the animal its advantage of surprise, I would retain

the upper hand

Crocodiles are the delta’s most feared aquatic

predator, but locals say that hippopotamuses cause

more deaths and injuries Accidental meetings in

narrow channels are often the trigger for an attack

Hippos can bite a canoe in half with one snap of

their jaws, and their teeth can puncture an

alumi-num boat as if it were a can

The two-ton vegetarians aren’t slowpokes, either

Guy Lobjoit, an Okavango fishing guide, told me he once had a hippo keep up with him while he was doing nearly 20 miles an hour in his runabout

Okavango’s Bounty

People have been living with the dangers and the bounty of the delta for at least 100,000 years The seasonal floodplain, the webbing between the delta’s toes, is a rich part of the Okavango larder Here the floodwater forms a lake six inches to a foot deep, dotted with countless islands The water brings a flush of plant growth, which in turn attracts wildlife into these fertile, sun-warmed shallows The local people make good use of the molapo, as the flood-plain is called During the flood they fish, and in the dry season they graze cattle All year round they harvest fruits, cut thatching grass and reeds, and hunt game on these productive lands

At Guma, near the top of the delta, a Bayei man known simply as Madala, Old One, and a young fishing guide called Fish took me into the molapo during the flood season to show me something of their way of life We journeyed by mokoro, or dug-out canoe, the mode of transport in the delta The mokoro that Fish poled was made from kiaat, a teak-like timber, with metal patches covering cracks

he called its wounds Madala’s canoe was fiberglass

He explained that the new synthetic canoes are more stable than the traditional wooden ones

More sustainable too, as trees suitable for making are a limited resource in the delta

mokoro-Poling is a hypnotically beautiful way to travel

Each thrust of the wooden pole moved the mokoro through beds of reed and sedge that rustled against the hull The foghorn snort of a hippo warned us to avoid its channel

As we poked along, Fish would point to various plants and describe their properties The root of the star apple makes an excellent toothbrush; the bark

of the rain tree can be ground up and thrown into the water to paralyze fish; chewed sickle bush leaves are good for treating snakebite Madala cut a tall papyrus stem and pounded the fleshy white base against his palm to soften it before handing it to me

to eat It was sweet, fibrous, and refreshing, niscent of fresh coconut

remi-● BELOW: In the crocodile’s lair, photographer Jennifer Hayes explores

caverns formed by floating mats of papyrus in the deep waters of the

Ncamasere channel in the Panhandle Croc tracks were everywhere

David Doubilet/National Geographic Image Collection

We made camp under the boughs

of a sycamore fig While Madala set

his net in a lagoon thick with water

lilies, Fish waded into the floodplain

to spear small fish with a porcupine

quill I climbed a baobab tree to

col-lect its maraca-shaped fruits

contain-ing a white pulp that substitutes well

for cream of tartar Madala mixed it

with water to make a tangy sauce

That night we rolled balls of cornmeal

porridge with our fingers and dipped

them in a casserole of freshly caught

bream, water lily fruit, and heart of

palm Other than the presence of a

few tourists—and a carton of long-life

milk for our tea—I suspected that

lit-tle in this scene had changed since the

first European explorers visited the

Okavango over 150 years ago

Water Life is coming

One thing that has changed—and continues to

change—is the path the water takes through the

delta In 1849, much of the flow was down the

western channel system and into Lake Ngami In

the 1880s the water flow, responding to a range of

subtle landscape cues, began to favor the eastern

channels The sluggish western channel became

choked with vegetation, and Lake Ngami dried up

The Batawana people, Botswana’s dominant tribe,

followed the water, shifting their main settlement to

a lush site on the delta’s southern edge They called

the place Maun, “place of reeds.”

Today Maun is a town of 45,000, with barely a

reed to be found Water flow seems to be moving

westward once more, and floods, which follow a

natural cycle of higher and lower volumes, have

diminished in size The result is this commercial

gateway to the delta has a water shortage It has

become a place of dust Not surprisingly, when the

annual flood does reach Maun (though there is no

guarantee that it will), the whole town celebrates

On a breathless July day—the sky the eggshell blue

of the Botswana flag, the air full of the smell of wild

sage—I watched as the flood crept down the broad,

dry bed of the river that runs through town

Children dug furiously with sticks in the sand to encourage the trickle to run faster Some leaped back and forth across the steadily widening stream, laugh-ing for joy Others just let it run over their bare feet, looking at it as if it was the first time they had seen water “The water is coming,” I heard a father explain

to his daughter “The fish are coming The water ies are coming Life is coming.”

lil-On a bank of the river, behind a twig fence that didn’t look as if it could keep out a goat, let alone a cow or a hippo, a man who told me his name was Flay Million Dube walked around his vegetable plot

He told me, “I’m not working today because I’m so happy.” He had just been down to the river to wash his face and hands in the new water, he said

Tomorrow he would put fresh, cool mud around his beds of spinach, broccoli, and kings onion

The dry season

By October the time of sadness has come The flood has vanished, ten billion tons of water sucked

up into the atmosphere whence it came People cast thirsty glances at the sky, where glowering thunder-clouds build in the afternoons, but the summer rains are still two months away The floodplains dry out, and water levels in the channels and lagoons drop to their lowest levels As the delta shrinks, life retreats

● ABOVE: Following the water, hundreds of African buffalo graze in

the lower delta during the flood Herds here reach into the thousands, their numbers regulated more by grass than predators.

Maun broils in temperatures of 100 plus Hot

winds sandblast the town, and the sky becomes

white with dust The Thamalakane River, where I

had witnessed the arrival of the new water three

months earlier, was again bone-dry Flay Million

Dube’s garden was bare soil, not a plant to be seen

No children played in the riverbed Only a few dust

devils whirled in the heat haze

Not since the 1960s has the Thamalakane flowed

all year round, delivering water to the delta’s outlet,

the once mighty Boteti River Fifty miles southeast

of Maun, at a camp called Meno A Kwena, all that

remains of the Boteti is groundwater, the legacy of

floods past Larger animals can dig for it, but with

each successive year of low flood volumes the water

table drops a little farther out of reach

David Dugmore, who runs the camp, has made

it a personal mission to provide water for at least

some of the thirsty animals—pumping groundwater

to fill a small water hole But his is only one small

relief station in a vast arid landscape Maintaining

the supply line is also a problem, he told me,

point-ing to lion tooth marks in the pipe that runs from

pump to pool “The lions are so desperate for water

they bite into the pipe, working their way along

until they reach the water hole.”

An hour’s drive down sandy tracks brought us to

a group of hippopotamuses stranded in a pond

There was no water for miles upriver or down, so the hippos were marooned There was little grazing

to be had, and it was with relief that we saw a life ranger drive up and unload half a dozen hay bales, which he cut open and spread beside the pool The hippos trotted out of the water and began

wild-to munch Were it not for their daily handout, they would starve

Is climate change casting its long shadow over the miracle delta? Apparently not, according to researchers, who have detected an 18-year oscilla-tion in rainfall in the region and an 80-year cycle

of high and low flood volumes We’re reaching the end of the 40-year low part of the cycle, they say, and should see larger floods in the future, peaking

in mid-century Rainfall should also increase over the next few years

River and rain contribute in roughly equal measure to the delta’s water budget The summer rains have the function of recharging the ground-water aquifer If the rains are good, little flood-water is needed to bring the water table to the surface, and the bulk of the inflowing water then spills into the seasonal floodplains, creating a large flooded area If the rains are poor, much of the floodwater soaks into the ground, filling the gap left by lack of rain, and the area of inunda-tion is reduced

● LEFT: One of the

many elephants that came from the south, lumbering toward the widening ribbon of water, trunk cocked in

an S, snuffing the sweet elixir Standing at the water’s edge, the thirsty animal sucked up trunk- fuls and gushed it into its mouth, spilling barely

a drop

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Influences on the Okavango

Terence McCarthy, a professor in the School of

Geosciences at the University of the Witwatersrand,

in Johannesburg, speaks of the delta as a living

organism with a circulatory system McCarthy and

his colleagues, who have been studying the delta

since 1985, have discovered that one of the largest

contributions to the life of the delta is made by one

of its smallest inhabitants: termites Their colonies

are giant construction companies that have

trans-formed the Okavango Delta from a piece of flat real

estate into a mosaic of an estimated 150,000 islands

It stems from the termites’ need for air-conditioning

Some species build above-ground air

vents to control the temperature in

their networks of galleries and

tun-nels These turrets, sometimes ten

feet high, and their surrounding

earthworks are above flood level,

providing dry, fertile sites on which trees can become

established

Trees can be thought of as kidneys of the delta,

cleansing the system by removing its salts They do

this by sucking water out of the ground and

pump-ing it into the atmosphere by transpiration In the

process, soluble salts are deposited around the tree

roots—a “toxic waste storage system,” McCarthy calls

it Without the delta’s millions of tree pumps, the

400,000 tons of salts carried in yearly by the

Okavango River would be poisoning the delta By

concentrating salts in the soil and groundwater

beneath them, trees not only keep the water in the

delta fresh but also expand the size of their island

platforms

Most channels in the delta have a life expectancy

of about a hundred years During that time sandy

sediment gradually raises the height of the channel

bed, slowing the current and allowing the fringing

stands of papyrus to spread into the channel Clumps

of papyrus eventually break off and jam the channel

until it becomes completely blocked At this point

the hippos come to the aid of the delta’s circulatory

system, breaking through papyrus jams and forming

new channel connections It is only because the delta

is so flat that water follows such randomly created

corridors—the paths the hippos have trod

Biological influences are part of a system as cate and responsive as any on Earth Yet the delta is not immune to human disturbance The chief threats lie upstream, in the two countries with which

intri-Botswana shares the inflowing water Angola and Namibia both experienced long, brutal wars in the latter part of the 20th century and now look to rivers

to help build their economies Two aspects of opment, the increased use of agricultural fertilizers and the production of hydroelectricity, could have disastrous downstream effects on the delta

devel-Papyrus can thrive in nutrient-poor conditions

Enrichment of the delta through fertilizer runoff

from irrigated farmland upstream could cause rampant growth of papyrus and lead to wholesale chan-nel blockage “If the Panhandle becomes blocked,” said Map Ives, of

a large tourism company, “it’s good night Okavango Delta.” Damming the rivers that supply the delta would be equally catastrophic

Scientists such as Terence McCarthy point out that dams deprive rivers of sediment that is vital to the functioning of the delta More than 200,000 tons of it

is deposited in the delta’s upper reaches each year, raising the channel beds and starting the process of channel switching by which the Okavango renews itself Without an annual injection of sand, channels would be scoured out instead of built up, becoming ever deeper and swifter Channel switching would cease; whole sections of the delta would be lost

I was near the grazing country of the Bié Plateau

It was November, and the summer rains were ing It was strange to think that the water flowing beneath me was bringing life to a distant delta But it was: In a few weeks the flood would start to rise in the Panhandle Relief would come to the Okavango’s parched plains The miracle would begin again

start-e X peditions activityResearch the use of fertilizers and the dams built north of the Panhandle since 2004 How have they affected the Okavango delta? What other measures might be taken to provide water to the area in a way that will not harm the ecosystem?

“IT WAS STRANGE TO THINK

THAT THE WATER FLOWING BENEATH ME WAS BRINGING LIFE TO A DISTANT DELTA.”

NASA

When the fiercest hurricane ever recorded in the Atlantic is bearing down on you, a salvaged armchair under a wood-and-tin awning might seem a poor choice of shelter But that’s where Don E (“I’d rather keep my last name out of it”) was parked when Wilma hit South Florida at 6:30 a.m October 24,

2005 For Don and a buddy, it was the start of the workday at Jimbo’s Place, a bait shop down by the water on Miami’s Virginia Key “Once we got out here, it was kind of too late to do anything but ride it out,” Don says.

Jimbo’s looks like nothing so much as an abandoned shack But whether through good luck or unexpectedly sound construction,

it survived Wilma’s fury Mercifully, the winds had ebbed from 185 miles per hour at sea to 120 miles per hour by the time the storm hit, but Wilma still left almost all of South Florida without power.

Season of Record Breakers

Wilma was a record breaker in a season of unsettling records Katrina, at the end of August, killed more than a thousand people and left much of New Orleans and the neighboring coast in ruins The damage exceeded a hundred billion dollars — the costliest natural disaster in U.S history — and the toll in fractured lives is incalculable Rita, in September, rivaled Wilma in intensity and ravaged the Gulf Coast through western Louisiana and East Texas

Super Storms

No End in Sight

● ABOVE: Year 2005: Never

before had a hurricane caused

as much economic damage as

Katrina Never before had the

Atlantic seen 27 named tropical

storms — so many that the list

of storm names had to be

extended with Greek letters

Seven made landfall in the

United States Never had 15

hurricanes been spotted in one

season, including four Category

5 storms Each image shows an

area 1,191 km (740 miles) wide.

● LEFT: As Hurricane Wilma

spun toward the Yucatán

Peninsula on October 19, 2005

(the day this image was shot

from the International Space

Station), a hurricane hunter

plane recorded an atmospheric

pressure of 882 millibars in the

eye of the storm The record

low drove winds of 185 mph.

Days after Wilma, one visitor to Jimbo’s was

already worrying about what future hurricane

seasons might bring Sharan Majumdar, 34, is a

hurricane researcher at the University of Miami’s

Rosenstiel School of Marine and Atmospheric

Science, just across the highway from Jimbo’s He is

one of a cadre of scientists trying to understand

nature’s most powerful storms and more reliably

predict their surges, ebbs, and lurching paths from

birth to landfall

Majumdar says he can’t really blame his fellow

patrons at Jimbo’s for deciding to stay put during

Wilma Forecasts can get hurricane tracks wrong by

hundreds of miles and wind speeds by tens of miles

per hour As a result, Majumdar says, “people often

return after an evacuation to find nothing really

happened.” The solution, he says, is to improve

forecasting through better science

“That’s the only way to get people to

trust the warnings.”

Why Hurricanes Form

Like all weather, hurricanes are

fueled by heat — the heat of sun-drenched tropical

seas, which powers the storms by sending warm,

moist air rushing toward the frigid upper

atmo-sphere like smoke up a chimney

As surrounding air is sucked in at the base of the

storm, Earth’s rotation gives it a twist, creating a

whorl of rain bands These whiptails of

thunder-storm activity are strongest where they converge in

a ring of rising, spinning air, the eyewall, which

encloses the cloud-free eye

Hurricanes (called typhoons in the western

Pacific and tropical cyclones in the Indian Ocean)

can propel themselves to an altitude of 15,240

meters (50,000 feet) or more, where the rising air

finally vents itself in spiraling exhaust jets of cirrus

clouds The largest ever, the 1979 Pacific typhoon

Tip, sent gale-force winds across more than 1,046

kilometers (650 miles) Even an average hurricane

packs some 1.5 trillion watts of power in its winds ,

or half the world’s electrical generating capacity

Starting this great weather engine requires

sur-face waters of 80 degrees or more, moist air, and

lit-tle wind shear — a difference in wind speed at the

surface and aloft that can tear apart a developing

hurricane But those ingredients often produce nothing more than a tropical disturbance — an unremarkable cluster of thunderstorms

“Disturbances look very similar day to day,” says David Nolan of the Rosenstiel School, “and then all

of a sudden you get a big burst of convection, then within six hours it becomes a depression, then it becomes a hurricane, then it’s flooding my apart-ment.” Katrina soaked Nolan’s 14th-floor Miami Beach home as the storm crossed Florida on its fateful course to New Orleans and the Gulf Coast

“It would be really nice to say what you need to make a hurricane,” he adds “And we really can’t do that yet.”

One thing was clear in 2005: Conditions were ideal for making hurricanes Yet 2005 was just a continuation of the upward trend that began in

1995 Because of a tropical mate shift that brought warmer waters and reduced wind shear, the Atlantic has spawned unusual numbers of hurricanes for nine of the past eleven seasons “We’re

cli-11 years into the cycle of high activity and landfall,”

National Oceanic & Atmospheric Administration (NOAA) meteorologist Gerry Bell says, “but I can’t tell you if it will last another ten years, or thirty.”

Hurricane Tracking Technology

Weather satellites make it easy for meteorologists

to keep tabs on hurricanes But ordinary satellite images show only the cloud tops Space-borne infrared sensors can reveal more detail, charting the size and shape of the warm eye, and satellite radar and microwave sensors can map the rain Hurricane hunter aircraft actually fly right into Atlantic hurri-canes But they only probe conditions at altitudes of several thousand feet, above the worst turbulence, Jack Beven of the National Hurricane Center (NHC) in Miami says — “not at the surface, where they really matter to people.”

In 2005, scientists flew a robotic aircraft straight into the maelstrom when tropical storm Ophelia was off the mid-Atlantic coast The craft, called Aerosonde, swooped and circled for ten hours, monitoring winds and the flow of heat and mois-ture from the ocean into the storm

“IT WOULD BE REALLY NICE TO SAY WHAT YOU NEED TO MAKE

A HURRICANE…AND WE REALLY CAN’T DO THAT YET.”

models to better forecast hurricane conditions In 2007,

a high-resolution NOAA hurricane Weather Research and Forecasting (HWRF) model became operational

morning of August 28 when Hurricane Katrina fied to Category 5 with an experimental model with an even higher resolution than the 2007 HWRF model.

intensi-That was a test, but forecasters routinely probe

the heart of storms with shorter lived devices called

dropsondes Released from high-flying aircraft into

hurricanes and the surrounding winds, these

instrument-packed tubes descend by parachute

“They take about 15 minutes from 12,192 meters

(40,000 feet) to splash,” Majumdar says Along the

way, they measure temperature, pressure, humidity,

and wind every half second, transmitting it all to

the airplane before they hit the water

By cranking dropsonde data into computer

mod-els that can simulate a storm and how it is likely to

evolve, researchers have sharpened their forecasts of

storm tracks Three-day forecasts of Atlantic storm

positions were off by an average of 708 kilometers

(440 miles) in the 1970s; by 2005 the average error

was 278 kilometers (173 miles) But one-day

fore-casts were still wide of the mark by an average of

113 kilometers (70 miles) — more than enough to

keep coastal dwellers second-guessing the experts

Shifts in Storm Intensity

Storm intensity is proving even harder to cast Three-day wind-speed forecasts, off by an average of 37 kilometers per hour (23 miles per hour) in the early 1990s, had improved only mar-ginally by 2005

fore-Hurricanes regularly surprise observers with their mood shifts In a matter of hours, a Category

5 storm (winds over 249 km/hr) can fade to a Category 3 (179–209 km/hr), or a mere tropical storm can explode into a killer “Intensity changes are the things that really hurt people,” says NOAA’s Bell

The state of the ocean below a storm explains some intensity shifts In 1995, tropical storm Opal was inching toward Category 1 status — an entry-level hurricane — as it made its way through the western Gulf of Mexico Then, in just 14 hours, it surged to Category 4 Satellite readings of the warm sea surface showed nothing unusual

(l)NGM ART/national Geographic Image Collection, (r)NGM ART/National Geographic Image Collection

● LEFT: Hurricanes Katrina and Rita

strength-ened dramatically when they crossed the Loop Current in the Gulf of Mexico Ocean probes showed that the Loop Current’s warmth extended to a depth of 91 meters (300 feet), increasing the supply of heat to the storms

The image shows the Loop Current three days before Katrina’s landfall The storm intensified

as it traveled over warmer waters (dark red).

But Nick Shay of the Rosenstiel School and his

colleagues discovered that the warm layer wasn’t

limited to the top few yards of the ocean, as it

usu-ally is in the Gulf Cold water at greater depths acts

as a brake on hurricane intensity when the winds

churn it to the surface But Opal had strayed across

a pool of warm water extending hundreds of feet

down No matter how hard the wind blew, it stirred

up more hurricane fuel, causing the storm to

intensify

The tropical ocean is littered with these deep warm

pockets, and their importance was underscored last

year by both Katrina and Rita, which shot up to

Category 5 when they passed over a deep band of

warm Gulf water called the Loop Current Satellites

can detect subsurface warmth by looking for subtle

bulges in the sea surface, Shay says “It’s not really

rocket science, but here’s something that works and

improves intensity forecasts by 5 to 15 percent.”

Waves, on the other hand, can blunt a storm

Whipped up by a hurricane, they can reach heights

of more than a hundred feet, exerting a drag on the

winds that created them “Heat adds fuel, but waves

slow the winds down — they’re fighting each other,”

says Shuyi Chen of the Rosenstiel School, who is

collaborating on a powerful new computer model, called the Hurricane Weather and Research Forecasting model, that will simulate the fine details

of the interplay between atmosphere, waves, and ocean “You can get a forecast one to two categories wrong if you don’t get the waves right.”

Forecasters also need to understand a hurricane’s internal workings Katrina, for example, had grown into a certifiable monster by the morning of

Sunday, August 28 Sucking energy from the Loop Current, the storm had screamed from the low end

of Category 3 to a peak of 175 miles per hour, well into Category 5, in just 12 hours And then, swiftly and remarkably, the storm took a breather In satel-lite images late Sunday, hours before landfall, a huge bite appeared in the southern side of the eyewall

Scientists probing the storm with aircraft and radar in a project called RAINEX worked out what had happened Katrina’s ferocious rain bands had converged toward the heart of the storm, cutting off the eyewall’s moisture supply The old eyewall broke

up and a new one formed farther out — an inertial brake that slowed the storm just as a skater’s arms slow her spin when she thrusts them outward

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