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00:00It's impossible not to be awed by the breathtaking landscape of America, with its ribbons of
00:09blue ice that seem to touch the sky, fiery fringes of islands still being formed, and
00:18towering mountains of sand that seem like they're part of another world.
00:23Each of America's natural wonders is a clue to unlock the secrets of the nation's fascinating
00:29geological past.
00:33In Yellowstone, boiling cauldrons of mud are evidence of a supervolcano that has the power
00:39to bring America to its knees.
00:43In Mississippi, a river's devastating floods are also what give life to one of the most
00:48fertile areas of farmland in the world, while in Utah, towering earthen forms reveal the
00:54remarkable power of erosion to sculpt the land.
01:01But the geological story of America is also full of twists and turns.
01:06In Arizona, it's taken millions of years to uncover the colorful layers that line the
01:11grandest canyon in the world, while nearby, a massive crater was blasted out of the desert
01:19in the blink of an eye.
01:21There are surprising wonders of nature in every one of the 50 U.S. states, from West
01:26Virginia, where a stunning spine of quartzite rose out of an ancient sea, to South Dakota,
01:33where badlands have preserved a treasure trove of fossils of the fascinating creatures that
01:38once roamed the Great Plains, all the way to Hawaii, home of the largest and most active
01:44volcanoes on the planet.
01:49Our fascination with nature's most breathtaking forms is why we climb them, explore them,
01:56and even risk our lives trying to reach their high, icy summits.
02:01This is the story of America's Natural Wonders.
02:19If there's one place to come in the lower 48 states to experience the raw and awesome
02:47power of the American landscape, it's here, the frozen high reaches of Washington State's
02:54Mount Rainier.
02:56There are more glaciers on this one mountain than on any other in the U.S. outside of Alaska.
03:02Twenty-seven different rivers of ice flow down from Rainier's Peak, but climbing just one
03:08of them can be a monumental task.
03:17Ice climbers are tethered together as they attempt Rainier's summit.
03:22All around them are giant crevasses that could swallow the entire team whole.
03:28An avalanche could bury them in seconds.
03:34Falling rock and ice have killed other climbers here before.
03:39More than 90 people have died trying to climb Rainier since it was first summited in 1870.
03:47But the real wonder of this mountain isn't the snow and ice that covers its peak.
03:52It's the powerful volcanic forces churning deep under Rainier that make it what some
03:57have called the most dangerous mountain in the nation.
04:04Rainier is the highest peak in a range of volcanic mountains known as the Cascades that
04:09runs along the Pacific coast from Canada to California.
04:14The Cascades have an extremely turbulent history.
04:18Nearly every volcano in the range has erupted within the last 2,000 years.
04:27The world came to understand the raw power of this mountain range on May 18, 1980.
04:36Early in the morning on that day, a 30-year-old volcanologist named David Johnston was monitoring
04:42Mount St. Helens in southern Washington state for the U.S. Geological Survey.
04:50He was positioned on a ridge almost 6 miles away from the peak, a site that was considered
04:55relatively safe since the volcano hadn't been active for more than 100 years.
05:04At 8.32 a.m., that all changed.
05:09A 5.1 magnitude earthquake suddenly rattled the mountain so intensely that the entire
05:14summit and north slope collapsed.
05:18It created the largest debris avalanche ever recorded on Earth.
05:22An enormous piece of the mountain was suddenly, simply, gone.
05:29Stunned by what he was witnessing, Johnston sent an urgent message to headquarters.
05:33Vancouver, Vancouver, this is it!
05:37Minutes later, Mount St. Helens erupted with catastrophic force.
05:42A cloud of superheated gas, ash, and debris raced down from the peak at 300 miles per
05:48hour right towards Johnston at his observation post.
05:51He had no time to flee or even send another message to Vancouver.
05:56His remains were never found.
05:591,300 feet of the peak had disappeared, and the once lush flanks of the mountain had been
06:06transformed into a stark and barren landscape, covered with ash.
06:12All the trees within 6 miles of the summit were destroyed.
06:17Many ended up in Spirit Lake, where they still float to this day.
06:26The eruption of Mount St. Helens was the deadliest volcanic event in U.S. history.
06:32It destroyed 250 homes and 27 bridges, and left 57 people dead.
06:41But the decades that followed have provided scientists with a unique chance to study the
06:45ways that ecosystems respond to the cataclysmic events that have shaped the American landscape.
06:54Just one year after the eruption of Mount St. Helens, herds of elk returned to the mountain's
06:59flanks.
07:00And as they foraged for food, their hooves disturbed layers of ash that helped plants
07:06buried beneath the ash sprout and grow again.
07:12Mountain goats were much slower to return.
07:14It took seven years for scientists to confirm sightings of this species here.
07:19Today, herds of these goats can now be found inside the volcano's crater.
07:24It's a story that's played out across the United States, time and time again, as massive
07:30forces have transformed the land, and plants, animals, and even people have had to adapt
07:36to their changing world.
07:39Those who hike up to the rim to peer down into the still-steaming cauldron of Mount
07:43St. Helens today come to be awed by the primordial forces deep under the earth that have the
07:49power to completely transform life above.
07:59One place on the U.S. mainland where it's possible to see those awe-inspiring forces
08:04in action is Yellowstone National Park, which straddles the border of Wyoming and Montana.
08:12It was the first national park in the world when it was created in 1872.
08:21This is Yellowstone's centerpiece, the Grand Prismatic Spring, the largest hot spring in
08:27the United States and the third largest in the world.
08:31Visitors here have to be careful.
08:33The clear blue water in the middle of the spring can reach 189 degrees Fahrenheit, hot
08:39enough to kill off almost all life.
08:42But amazingly, some types of bacteria are able to survive this extreme heat, and it's
08:48those different species of bacteria that give the Grand Prismatic its rainbow of colors.
08:56But this breathtaking sight is much more than just a colorful wonder of nature.
09:01It's also evidence of the terrifying powers that lie under Yellowstone itself, powers
09:07that could threaten the very existence of life in North America as we know it today.
09:16The giant basin that holds Yellowstone Lake and much of the park is actually the crater
09:21of a supervolcano and one of the largest active volcano systems in the world.
09:28Deep under Yellowstone are giant chambers of superheated magma that are slowly rising
09:34towards the surface of the Earth.
09:36The largest of these chambers is believed to be up to 28 miles deep and to contain enough
09:41magma to fill up the Grand Canyon 11 times over.
09:46After the Yellowstone volcano's last major eruption 640,000 years ago, its giant caldera
09:52filled in with lava and later, plants, which is why Yellowstone is just one enormous valley
09:58today.
10:00But some have called it one of the Earth's largest ticking time bombs because of its
10:04potential power and the impact that its ash cloud could have on life on Earth.
10:10Government scientists don't have any evidence that Yellowstone will erupt any time soon,
10:15but they've tried to map what could happen if it does.
10:19Most volcanologists agree that a major eruption of Yellowstone's supervolcano would be catastrophic.
10:26Inside the 600-mile radius of the volcano, an area called the kill zone, 90% of people
10:31and animals could die.
10:33Layers of hot ash would cover the ground for as much as 1,000 miles all around the crater.
10:39More ash could eventually spread out across most of the United States, killing crops,
10:44collapsing buildings, blocking out the sun, and making air, rail, and car travel impossible.
10:51A major eruption of Yellowstone could bring America to its knees.
10:59Millions of people visit this national park every year.
11:02Many are not aware that they are standing right on top of a massive, rising chamber
11:06of superheated, molten rock.
11:09But they sense its power thanks to Yellowstone's geysers.
11:17When water deep underground is heated by the magma, it boils, but the steam often can't
11:23escape to the surface because it's trapped by water and rock.
11:28So it pushes the water above it, upward, through whatever channels it can find, until it erupts
11:34from the surface in the form of geysers.
11:39Yellowstone has half of all the known geysers in the world, roughly 300 in all.
11:45This one, the Klepsydra geyser, shoots up as high as 40 feet.
11:51There are also more than 10,000 other thermal features in Yellowstone.
11:56They include giant cauldrons of boiling mud that look like simmering primordial stews
12:02and stop tourists in their tracks.
12:05And there are hundreds of vents that release steam from deep below.
12:10They are all part of the wonder of Yellowstone.
12:18Just as this mother grizzly bear is, with her cubs, far away from the well-beaten trails
12:24of this national park.
12:26She is one of the more than 600 grizzlies that live in the Yellowstone region, and one
12:31of the many species for which the park is famous, including wolves, bison, and elk.
12:41More than three decades before Yellowstone became a national park, settlers started making
12:46their epic journeys across the Great Plains, hoping to reach the promised lands of Oregon
12:52and California.
12:55Many of them eagerly awaited the moment when they would set eyes on this.
13:05The towering spire of Chimney Rock.
13:11This landmark was the first sign to the exhausted settlers that they were finally arriving in
13:16the West.
13:18It was the first of many dramatic natural forms they would soon pass by.
13:23Forms that still dazzle travelers today.
13:32From Colorado's River of Red Rocks, that line the base of the Rockies, right where the mountains
13:38touch the plains, to the towering forms of Utah's Chocolate Drops,
13:47that stand like ancient sentinels in Canyonlands National Park,
13:55to the colorful drip castles of Bryce Canyon, created by erosion over tens of thousands
14:02of years.
14:05There's no end to the natural wonders of the American West,
14:12but the landscape of the Eastern United States can be just as dramatic, and has some of the
14:18most fascinating natural forms on the continent.
14:25This stunning spine of quartzite that shoots up out of the forest of West Virginia is one
14:31of them.
14:34It's known as Seneca Rocks.
14:38These jagged bridges started to form more than 400 million years ago, when the eastern
14:43edge of North America lay under an ancient sea.
14:49Over time, sediment from that sea was compacted and pushed upward into towering mountains.
14:58The rugged peaks of Seneca Rocks emerged when the earth around them eventually eroded.
15:06Today, they are one of the most breathtaking sights in the eastern United States, and a
15:12haven for rock climbers eager to reach Seneca Rock's highest peak, which towers a thousand
15:18feet over the valley below.
15:22During World War II, the U.S. Army's elite mountain training group used Seneca Rocks
15:28for its low-altitude assault climbing school.
15:31Its isolation and terrain was similar to what U.S. forces were likely to encounter
15:36in the Italian Alps and other European countries.
15:44Seneca Rocks lie in the Appalachian Mountains.
15:47Once, these mountains served as a formidable barrier to early settlers trying to stake
15:53out claims on America's western frontier.
15:56Today, they are home to one of the most legendary hiking routes in the nation, the Appalachian
16:02Trail.
16:04For northbound hikers, it starts here, at a bronze plaque beneath the trees on Springer
16:10Mountain in Georgia.
16:13The Appalachian Trail then runs for roughly 2,000 miles northeast, across parts of 13
16:20states.
16:20It takes about six months for most hikers to make it all the way to Maine, where the
16:25trail ends at Mount Katahdin.
16:28The Appalachians are some of the oldest mountains on Earth, and form the second-longest mountain
16:33range in North America, after the Rockies.
16:41Today, the Appalachians are a fraction of the size they used to be.
16:49Giant volcanic events in the range once created mountains as high as the peaks of the Rockies.
16:57But since the Appalachians are much older than their western cousins, they've had much
17:01longer to erode.
17:04Their towering peaks have been whittled down to mountains that often look more like just
17:08rolling hills.
17:10Today, they serve as a reminder of the dramatic transformation that the eastern United States
17:16has undergone over the last 500 million years.
17:20And great change is still underway all across the lower 48, and beyond.
17:31Especially on the fiery fringes of Hawaii.
17:39This is the southeastern coast of the largest island in the Hawaiian archipelago.
17:48It's known simply as the Big Island.
17:52It's the only place in America where it's possible to see an island being created by
17:56volcanic activity.
17:59As streams of boiling lava reach the sea, they trigger giant clouds of steam.
18:05Then the lava cools and hardens in place, causing the island to grow bigger and bigger.
18:14This was how Hawaii's islands were originally created, by volcanoes deep below, pushing
18:19up above water, and over millions of years, building more and more volcanic land.
18:26The source of all this land building today is one of the Big Island's five legendary
18:32volcanoes.
18:33This is the steaming cauldron of Kilauea.
18:36In 1983, lava started spewing out of this ancient crater, and it's never stopped.
18:43Those smoking rivers of lava have made Kilauea the most active volcano on Earth.
18:52Up to 650,000 cubic yards of lava are belched out of it every day.
18:57That's enough to fill up about 60,000 cement trucks.
19:02There are three active volcanoes on the Big Island.
19:05One of them is the largest volcano in the world, Mauna Loa.
19:13It covers more than 2,000 square miles.
19:17Mauna Loa rises 13,678 feet above sea level.
19:22But if you measured it from its base on the seafloor of the Pacific Ocean, this mountain
19:27is taller than Mount Everest by more than three-quarters of a mile.
19:32There's nothing like looking down on Mauna Loa from the air, and imagining the forces
19:37that it took to create this immense crater, and the Hawaiian Islands themselves.
19:46But Hawaii's volcanoes are very different from those on the U.S. mainland.
19:52Most of America's biggest volcanic eruptions have occurred where the Pacific plate clashes
19:56with other plates around it.
20:00This creates a zone of volcanic activity that reaches up from Chile in South America, along
20:05the Pacific coast of the U.S. to Alaska, and then over and back down past Japan and the
20:12Philippines, all the way to New Zealand.
20:15It's known as the Ring of Fire.
20:18But the volcanoes of Hawaii lie in the middle of the Pacific plate, and are triggered by
20:23different forces, known as volcanic hotspots.
20:28A hotspot is a place where molten rock or magma is forced up through cracks in the Earth's
20:34crust.
20:36The lava that flows out of the Hawaiian hotspot is highly fluid, which helps explain why volcanoes
20:42like Mauna Loa are not towering peaks like their cousins along the Ring of Fire.
20:49The lava here is so fluid, it keeps running downhill until it reaches the sea.
20:55Even after hundreds of thousands of years, the volcano itself is still just a low, wide
21:00dome that resembles a rounded shield from above, which is why they are called shield
21:06volcanoes.
21:13The Big Island is the youngest of the Hawaiian Islands.
21:16It's only about half a million years old.
21:19But part of the great wonder of the Hawaiian archipelago is the tremendous contrast between
21:26its younger volcanic landscapes, which can appear seemingly devoid of life, and places
21:33like this, the lush, tropical terrain of the much older island of Kauai.
21:41Eruptions of the Hawaiian hotspot first created Kauai's rugged, towering peaks, which lie
21:47in the Hawaiian Emperor Volcanic Range.
21:50But after volcanoes built these mountains, it was erosion that etched and shaped them
21:56into the dramatic forms they are today.
22:02Kauai is roughly 5 million years old, and is the oldest of the Hawaiian Islands.
22:08Since it's the northernmost island, Kauai gets battered 70% of the year by trade winds,
22:14tropical storms, hurricanes, and seasonal cyclones called Kona storms, found only in
22:20Hawaii.
22:22About 450 inches of rain fall every year on Kauai's Mount Waialeale, which makes it one
22:28of the wettest places in the world.
22:32Kauai is famous for its waterfalls.
22:36Including this one, the Manawaiapuna Falls.
22:41Many know this majestic waterfall for its brief appearance in the Steven Spielberg film
22:46Jurassic Park.
22:51There's nothing like flying through Waimea Canyon State Park on the northwest side of
22:54Kauai.
22:57Its deep valleys and canyons were scoured by water over millions of years.
23:02But all this erosion has also unearthed enormous amounts of nutrients buried in Kauai's volcanic
23:08soil.
23:09Those nutrients have made it possible for a rich diversity of plant species to thrive
23:14here.
23:15And one reason Kauai is known today as the Garden Island.
23:23It's taken the Hawaiian Islands millions of years to grow to the sizes they are today.
23:29They are like many of the other most impressive landscapes in the United States, created millimeter
23:34by millimeter, inch by inch, over a time period that can be hard to comprehend.
23:47But fly across the desert of eastern Arizona, and you discover that giant forms in the land
23:54can also be created in mere seconds.
23:58This vast, one-mile-wide, 550-foot-deep depression is known today as Meteor Crater.
24:06Before there were any humans in North America, this enormous bowl of earth and rock was formed
24:12in the blink of an eye.
24:19It happened 50,000 years ago, when a meteorite traveling at 26,000 miles per hour crashed
24:25through the earth's atmosphere and slammed into the Arizona desert.
24:30Its impact created an explosion that was 150 times stronger than that of an atomic bomb.
24:38The meteorite itself melted on contact and sprayed molten metal and pulverized rock a
24:43mile out in every direction.
24:47Some of that rock has helped scientists determine that the earth is roughly 4.5 billion years
24:52old.
24:54Meteors, like the one that crashed here, were created at about the same time as the earth
24:59itself, but are made from rock whose origins can be more easily dated than even the oldest
25:04rock in places like the bottom of the Grand Canyon.
25:11It's impossible to know what Arizona's early people, the Sinagua, thought of the Meteor
25:16Crater and how they believed it was formed, but we do know that they witnessed other major
25:21events that shaped the land around them.
25:25Nine hundred years ago, the Sunset Crater volcano erupted and forced many of the Sinagua
25:31to flee.
25:34This impressive volcanic form and the giant bowl of the Meteor Crater lie just 50 miles
25:39away from each other, and provide two powerful illustrations for the rich, more than 4 billion
25:46year old story of planet earth.
25:54Catastrophic events, including volcanic eruptions, the impacts of meteorites and massive earthquakes,
26:01often serve as markers for geologists, historians, and others, of moments of great change in
26:07our natural world.
26:10But the fact is, the American landscape is still being formed, sculpted, and shaped all
26:16around us every day.
26:24Some of the biggest forces driving that change are America's great rivers. Rivers like the
26:30Missouri, which is the longest in the U.S.
26:35It flows 2,341 miles from Montana all the way down to its convergence with the Mississippi
26:42River here on the border of Missouri and Illinois.
26:47The Missouri River is nicknamed the Big Muddy because of its raw earth carving power. As
26:53it flows, this big, wide, powerful waterway devours the soil in the fields, farms, and
27:00ranches that line its banks. It's been called the hungriest river ever created.
27:08Due to all the silt in its waters, Mark Twain is reported to have said, the Missouri River
27:13is too thick to drink and too thin to plow.
27:18But while the Missouri may rip and tear at the land along its banks, the Mississippi
27:25River is famous for simply overrunning them.
27:30Here in the state of Mississippi, animals head for high ground whenever the river's
27:35waters rise. And for thousands of people who live near this legendary waterway, floods
27:43can destroy homes, livestock, and even an entire year of crops.
27:51But while the Mississippi's waters can be terrifyingly destructive, they have also made
27:58the land around the river some of the most fertile in the world.
28:05Over millennia, floods and the river itself spread layer after layer of nutrient-rich
28:11silt all around the Mississippi. This extremely fertile land, now called the Mississippi Delta
28:19Region, stretches from southern Missouri down to Louisiana.
28:29Today a wide range of crops thrive here, including rice and soybeans.
28:38But before the Civil War, this fertile region was the heart of the cotton industry. Millions
28:44of enslaved Africans once worked the fields here, and made the U.S. the biggest producer
28:49of cotton in the world.
28:53The Mississippi Delta Region was also where the blues were born. It arose out of the songs
28:59African Americans sang in the fields, and was part of the vibrant culture they developed
29:04to transcend hard times, including devastating droughts as well as floods.
29:12Rivers have played a big role in shaping the land and culture of the United States. But
29:17once, most of what's now North America itself lay underwater.
29:2295 million years ago, much of what is now North America was covered by a vast inland
29:27sea known as the Western Interior Seaway. To the east was a landmass geologists have
29:34named Appalachia, and to the west another they called Laramidia. Between these two landmasses
29:42and underwater lay the region that's now the Great Plains.
29:5070 million years ago, continental plates of the Earth's crust collided and started to
30:02rise. Eventually, the inland sea drained away. Today, there are sites all across the Great
30:10Plains region that hold evidence of those ancient waters.
30:16South Dakota's famous Badlands is one of them. These dramatic, jagged forms are made up of
30:23sedimentary rock. The oldest layers were formed by mud and the bones of sea creatures as they
30:30settled on the sea floor. After the inland sea disappeared, subtropical forests covered
30:38the land here, and laid down new layers of sediment. Later, rivers flooded, depositing
30:45even more earth, rock, and bones. In layers of sediment here, archaeologists have unearthed
30:52the fossils of fascinating creatures that once called North America home, from ancient
30:57sea clams, to alligators, and even three-toed horses. These Badlands are fast eroding, and
31:05scientists believe they will be completely gone in about 500,000 years. That's roughly
31:12the same time it's taken volcanic forces to create the Big Island of Hawaii.
31:20When large bodies of water evaporate, or are forced to drain away, the raw materials left
31:26behind can be perfect building blocks for nature to create stunning new, wondrous forms
31:32in the land.
31:39That's what happened here, in the San Luis Valley of southern Colorado. A vast lake once
31:47covered this 7,000-foot-high valley, which is protected by the Sangre de Cristal Mountains
31:52to the east, and the San Juan Mountains to the west. But that ancient lake evaporated,
31:59and then, wind started to whip up the sand that once lined the floor of the lake. Over
32:06time, all that sand ended up here, and created what's now the Great Sand Dunes National Park.
32:16It has some of the tallest dunes in the United States. They tower 750 feet above the floor
32:23of the former lake.
32:26When explorer Zebulon Pike arrived here in 1807, it could have been on a day like this
32:31He wrote that the appearance of the dunes was,
32:35exactly that of a sea in a storm. It would be easy to spend an entire day walking the
32:42ridges of these mountains of sand, and forget that without water, this desert environment
32:48would never have been formed.
32:55Part of the wonder of the American landscape is that similar geological processes have
33:00given birth to an endless variety of different shapes and forms. Sand dunes are a perfect
33:07example. They can be found across the nation, but no two are alike.
33:15These giant dunes in northern Nevada look like the enormous spine of an ancient sea
33:20creature, left stranded when the waters around it disappeared. In California's Death Valley,
33:28the remote Eureka Dunes rise above the floor of a former salt lake.
33:36And here on California's southern border with Mexico, a steel border fence runs right across
33:42shifting ribbons of sand that once lay at the bottom of a tropical sea.
33:50When Spanish explorers first started traveling north from what's now Mexico, they did whatever
33:56they could to avoid this forbidding region. Today, this landscape of sand is one of the
34:02toughest sections of the U.S.-Mexican border to cross for human smugglers.
34:12The surface of the Earth has so many different forms, shapes, and colors that it's not hard
34:17to understand why early scientists had a hard time determining what was responsible for
34:22creating and shaping our natural world. In the early 19th century, most European scientists
34:35believed that volcanoes and earthquakes were the primary forces that created the landscape
34:39around us, from the highest mountains to the deepest valleys and the vast open spaces that
34:47lie in between. But in 1858, an American geologist named John Newberry changed that thinking
34:59after he arrived in the Grand Canyon.
35:07He came on a surveying expedition for the U.S. government. At the time, the Grand Canyon
35:21didn't even appear on many maps. It was part of a region written off simply as the Great
35:27Unknown. Newberry was the first scientist ever to descend down to the canyon's floor.
35:35Once he set eyes on the Colorado River and studied the colorful layers of rock that towered
35:40above him, he proposed that the river itself had carved the canyon. It was a radical theory
35:47for the middle of the 19th century. It suggested that it would have taken millions of years
35:53to carve the canyon, which would mean that the Earth had to be much, much older than
35:59most people imagined. Today, most scientists agree that Newberry was right about how the
36:07canyon was formed. It all began about 6 million years ago, when the Colorado River first began
36:14flowing down and out of the Rocky Mountains and started carving a path through the Colorado
36:19Plateau.
36:26Over time, it sliced deeper and deeper into the Earth, inch by inch. But one reason that
36:32the Colorado River was able to create a one-mile-deep canyon was because the land itself was also
36:38rising. Tectonic plates in the Earth's crust were forcing the Colorado Plateau upward.
36:48As layers of sedimentary rock beneath the Earth were forced to rise, the Colorado River
36:54kept scouring a deeper and deeper canyon through those layers. Meanwhile, hundreds of smaller
37:03rivers and streams started flowing into the canyon from the surrounding land. Those streams,
37:11together with wind and rain, ultimately eroded the Earth of the Colorado Plateau and helped
37:18create the vast, 18-mile-wide canyon we see today.
37:29The scale, colors, and forms of the Grand Canyon are a feast for the eyes. Whether you're
37:36floating down the Colorado River and looking up at its walls, or standing on its rim and
37:44peering into the abyss, Harper's Magazine once described it as Beethoven's Ninth Symphony
37:51in Stone and Magic Light.
38:01Naturalist John Muir famously called the Grand Canyon a grand geological library, because
38:07for geologists, it's a window into hundreds of millions of years of the Earth's history.
38:16Today, these black rocks that line the Colorado River are the oldest rock layers in the canyon.
38:23They are known as Vishnu Schist, and are up to two billion years old. They were formed
38:29by the fusion of volcanic ash and sediment from an age when much of the area that became
38:34North America was covered by the sea. Heat and pressure melted those sedimentary materials
38:41into the rocks we see today.
38:45Higher up on the canyon's walls, scientists have identified at least 40 other layers of
38:50rock, each of which holds clues to help understand how changes in climate and weather have radically
38:56altered the land.
38:59Today, the Grand Canyon is still being formed. The Colorado River continues to scour the
39:05canyon floor, while smaller tributaries are still eroding and widening the canyon every
39:11day, just as they've been doing for millions of years.
39:22Rivers and erosion transformed this region of what's now the Arizona Desert. But it was
39:28ice that radically altered the landscape of many other U.S. states, starting roughly
39:33100,000 years ago, in a period known as the Last Ice Age.
39:40By 70,000 years ago, giant sheets of ice were spreading across the northern hemisphere of
39:46planet Earth. In North America, the vast ice sheet known as the Laurentide ended up covering
39:53almost all of Canada. It reached down as far as what are now the states of Missouri, Illinois,
39:59and Indiana in the Midwest. But when it finally retreated roughly 10,000 years ago, it left
40:06behind five of North America's natural wonders, the Great Lakes, Ontario, Erie, Huron, Michigan,
40:15and Superior.
40:20The enormous basins in the Earth that hold the Great Lakes were created by the tremendous
40:25weight of the Laurentide ice sheet. When the planet warmed and the ice retreated, those
40:32glacial depressions then filled up with meltwater. Today, the five Great Lakes contain 21 percent
40:41of the world's fresh water. The largest of them is Lake Superior. There's enough water
40:48in this one lake to cover North and South America one foot deep.
40:55The Great Lakes are so big, they are almost like freshwater oceans, which is also why
41:00lighthouses stand tall on their shores, to guide ships in what can be very rough waves
41:06and weather. When the glaciers originally plowed across the land that's now the Great
41:13Lakes, they pushed enormous ridges of earth, rock, sand, and clay ahead of them. After
41:19the ice melted, these ridges were slowly worn away by waves and rain. Wind then blew tiny
41:28grains of sand up into the towering dunes that line the shores of Lake Michigan today.
41:35One of the most famous of these dune systems is the Indiana Dunes National Lakeshore. It
41:44stretches on for 15 miles, right up to the border of Illinois, and creates a surprising
41:50sight in the middle of the Midwest. But the tallest of these mountains of sand lie further
41:56north. These are Michigan's Sleeping Bear Dunes, one of the state's most beloved natural
42:04wonders, where it's possible to race down nearly 100 feet of sand in a spot that's been
42:10named the most beautiful place in America. The Ice Age created breathtaking natural forms
42:20all across the northern states, including the Boundary Waters Canoe Area Wilderness
42:26in northern Minnesota, where thousands come to paddle through one of America's most unique
42:31watery worlds. To the south, the Ice Age is the reason that the farmland of Illinois
42:38is so incredibly flat. Glaciers simply leveled it. Evidence of the last Ice Age can be found
42:46further east, in New England too. The famous Kettle Lakes of Cape Cod and Massachusetts
42:53are like many versions of the Great Lakes. They too were carved out of the earth by glaciers.
43:01Even the Cape of Cape Cod was sculpted by glacial ice. And to the north, a nearly one
43:09mile thick glacier once covered the entire state of Maine. Most of Maine's landscape
43:16was shaped in some way by glacial activity. From the beautiful coastal inlets and harbors
43:22that were left behind when the ice finally melted, to the rocky shores of Mount Desert
43:27Island, home to Acadia National Park. During the last Ice Age, so much of the earth's
43:37water became trapped in glacial ice that the world's oceans dropped 400 feet. Here in
43:48Maine, fishermen working miles offshore have pulled up the bones and teeth of mastodons,
43:54giant sloths, and ancient walruses in their nets. These species once inhabited islands
44:01that were eventually submerged with water when the glacial ice sheets melted and the
44:06sea levels rose. But the last Ice Age isn't just ancient history. Most of today's glaciers
44:16are also retreating, almost everywhere they can be found in North America and the world.
44:25Fly across the United States, and sometimes it can seem like you're entering worlds that
44:32have never been touched by humans. One of those is Montana's Glacier National Park.
44:42Seventy million years ago, colliding tectonic plates started to thrust these enormous peaks
44:47into the air. Then, colossal glaciers that have since melted scoured the deep valleys
44:55that make Glacier National Park one of the most majestic landscapes in the nation. There
45:03are 150 peaks here that top out above 8,000 feet, and then plunge down to clear mountain
45:11lakes that fill many of Glacier's valleys. Soar across this National Park today, and
45:22it's easy to see that the younger alpine glaciers here are undergoing rapid change. In the middle
45:31of the 19th century, there were 150 glaciers left in these mountains. Today, only 25 remain,
45:39and they're melting fast. Some are now so small, they don't even look like glaciers
45:48at all, just fields of snow. As these mountains emerge from tens of thousands
45:57of years of icy hibernation, life is returning to their flanks. Lush forests and fields now
46:04cover steep slopes that were once frozen under ice. Scientists say that by 2030, all the
46:16glaciers in Glacier National Park will be gone. Flying over northern Montana, it can
46:24be hard to fathom what Glacier National Park looked like when it was completely covered
46:35with snow and ice. But it's a sight that pilots in Alaska are used to seeing every day, especially
46:44those who soar across the peaks of the St. Elias Mountains, and set eyes on this. The
46:53Bagley Ice Field. It's the largest non-polar ice field in North America. The Bagley is
47:01essentially a giant bathtub of solid ice. It's 120 miles long, 6 miles wide, and in
47:09some places, a half a mile thick. Ice fields are created at high elevations where it's
47:15too cold to rain. But as snowfall accumulates over time, it gets compacted under new layers
47:22of snow, and gradually turns to solid ice. Ice that will eventually be the source of
47:29glaciers. It can be hard to see from above, but the ice in this giant bowl is actually
47:35flowing out into valleys between the surrounding mountains as glaciers. The Bagley is a giant
47:43in the world of ice, so it's not surprising that the glaciers it spawns are giants too.
47:51One of them is the largest and longest glacier in the world. The Bering. At its mouth, this
47:58one glacier is 10 miles wide. Every year, it releases six and a half trillion gallons
48:05of water into the Gulf of Alaska. There are few natural environments as forbidding to
48:13humans as the treacherous surface of giant glaciers. Flying across the Bering is the
48:20only way to peer down into the thousands of deep and shifting crevasses that make up this
48:25glacier. Just one of these could easily swallow people and even aircraft whole. At its highest
48:33reaches, there are pools of meltwater, and deceptive narrow cracks into which even the
48:39most experienced adventurers could disappear without a trace. Thanks to the raw power and
48:49danger of Alaska's natural spaces, it's known today as the Last Frontier. Every year, more
48:59than a thousand mountain climbers lift off from the small town of Talkeetna. They come
49:07to attempt the summit of the highest mountain in North America, Denali. This snowy peak
49:17towers 20,310 feet into the air. But the climbers' trek to the summit really starts at the Denali
49:25Base Camp. From here, teams head out to try and conquer the icy flanks of this majestic
49:32peak. Less than half will succeed in reaching the summit. More than 120 people have died
49:39climbing Denali's peak from altitude sickness, exposure, falls, and avalanches. But it's
49:52not hard to understand the thrill of attempting to climb this breathtaking mountain for the
49:57chance to set foot on the highest spot on the continent. It's the ultimate place to
50:04appreciate the fascinating geological story of America, and the forces that have created
50:09the nation's most impressive landscapes. From the enormous rivers of ice that crash into
50:17the sea, to its towering volcanic forms, right down to the islands that line its stunning
50:24shores, these are America's natural wonders.
50:54For more information visit www.fema.gov