Eight-Thousand Meter Peaks As Seen From Orbit
Eight thousand is a perfectly arbitrary number. Yet, no other number looms larger for mountain climbers.
By Adam Voiland, Design by Robert Simmon -- Fourteen mountain peaks stand taller than 8,000 meters (26,247 feet). There could have been many more of these "eight-thousanders" if the French commission that established the length of the meter (in 1793) had made it just a bit shorter; there would be hardly any if they had made the meter longer. The decision to make a meter equivalent to one ten-millionth of the distance between the equator and the North Pole left the world with fourteen 8K peaks. All of them are found in either the Karakoram or Himalayan mountain ranges of central Asia.
Fourteen is a number that pushes climbers to the point of obsession. It's big enough that only the most ambitious consider climbing all of them, but small enough that doing so over a lifetime still seems possible. Even in the United States, a country where most people shun metric measurements, climbers dream of ascending the eight-thousanders. The "twenty-six-thousand, two-hundred-and-forty-seven-footers" hardly has the same ring.
These photographs from the International Space Station show Annapurna and Manaslu (top) and the central Karakoram, the highest concentration of 8,000-meter mountains on Earth. (Astronaut photographs ISS025-E-011510 and ISS037-E-017916 courtesy NASA/JSC Gateway to Astronaut Photography of Earth)
However you measure them, the world's tallest mountains are treacherous. They have towering blocks of ice--seracs--that can crush climbers in seconds. They are prone to tremendous avalanches of rock and snow that obliterate entire expeditions. And they are home to spider webs of ice crevasses that swallow humans whole. Even during the summer, average daytime temperatures are frigid. And, hurricane-force winds are common.
Then, of course, there is the lack of oxygen. At 5,000 meters (16,404 feet), the atmosphere contains about half as much oxygen as at sea level. By 6,000 meters (19,685 feet), the air is so thin that full acclimatization is no longer possible. No matter how fit, climbers begin to slowly suffocate. By 7,000 meters (22,966 feet), survival times plummet and lucid thought becomes difficult. By 8,000 meters--the so-called "death zone"--even the strongest climbers can survive for a few days at best.
The three most dangerous of the eight-thousanders--Annapurna, K2, and Nanga Parbat--claim the life of about one climber for every four who reach the top. The fatality rate for Annapurna, the most dangerous mountain in the world, is over 30 percent. Bottled oxygen and guided climbs have made Mount Everest much safer than it was decades ago, but the world's tallest mountain still takes lives regularly. Nine people died on the mountain in 2013. Ten in 2012.
All this risk is for what, exactly? Reinhold Messner, the first person to climb all fourteen of the eight-thousanders, pointed to something he calls "overview" to explain the allure. "It is not the mountain but the view from the peak that suggests increased awareness," he writes in the book Mountains from Space. "The person who stands on top of one comes back down with a new sense of the world."
Messner risked everything for fleeting views from the top of the world, ascending many of the eight-thousanders solo and without the aid of bottled oxygen. It took him 16 years (1970-1986) to climb them all. Only 31 other people--give or take a few because the records of some climbers are considered controversial--have done it since.
While the summit of an eight-thousander may represent the ultimate view on Earth, satellites take Messner's concept of overview to a whole new level. The summit of Mount Everest is about 8.8 kilometers (5.5 miles) above sea level. Most polar-orbiting satellites fly at an altitude of 705 kilometers (438 miles). So when viewed from space, the world's tallest mountains become blotches of shadow, rock, and snow. Epic glaciers become narrow tongues of ice feeding glacial lakes that look like puddles. Deadly storms become mere tufts of cloud.
Ground photography of Mount Everest and the other tall peaks are ubiquitous, but the gallery that follows--a collection of imagery acquired by the Advanced Land Imager (ALI) on NASA's EO-1 satellite--offers a less familiar perspective. The sensors on ALI looked directly down on the mountains, not from an oblique angle like a passenger on an airplane or an astronaut on the International Space Station might see them.
The tallest mountains in the world are the result of a collision between two tectonic plates. As the Indian Plate smashes into the Eurasian Plate, the crust along the line of impact buckles. The final height of the mountains is dictated by the balance between the rate of uplift and erosive power of ice. (NASA Earth Observatory maps by Robert Simmon, using data from the Blue Marble and GTOPO30.) In some ways, this top-down view makes the images difficult for human eyes and brains to interpret. Scenes appear strangely flat. Separating a mountain's summit from the ridge is challenging. Vast shadows obscure features in adjacent valleys, and opaque snows blanket everything.
Yet, in other ways, the view from directly above is the most valuable of all. Images like these make clear that the world's tallest peaks are not isolated pyramids. Rather, they are part of long, sinuous ridges that stretch for such distances that it can be difficult to tell exactly where the summit lies.
With structures as massive and complex as mountains, distance provides clarity. Faults, suture points, glaciers all emerge--helping geologists piece together the story of how physical processes created these extraordinary mountains and continue to shape them today.
The geological story is one that began some 40 million years ago when the Indian subcontinent began a slow-motion collision with Asia, jamming the edges of the two continents into the massive ridges and valleys that make up the Himalaya and Karakoram today.
"If you want to understand how mountains form, these ranges offer a perfect laboratory. These are the youngest, most dramatic, and fastest uplifting mountains in the world," said Michael Searle, a University of Oxford geologist and a veteran of dozens of expeditions to the Himalaya and Karakoram. But it was journalist John McPhee who summed up the wonder of their geologic history when he wrote the Annals of the Former World, his Pulitzer prize-winning history of Earth's geology: "The summit of Mount Everest is marine limestone," he extolled. "This one fact is a treatise in itself on the movements of the surface of the Earth. If by some fiat, I had to restrict all this writing to one sentence; this is the one I would choose."
In other words, when climbers reach the top of Mount Everest, they are not standing on hard igneous rocks produced by volcanoes. Rather, they are perched on softer rock formed by the skeletons of creatures that lived in a warm ocean off the northern coast of India tens of millions of years ago. Plate tectonics transformed ocean bottoms into the highest points on the planet. It's just one of many bizarre realities of the eight-thousanders, mountains that will continue to fascinate scientists and obsess climbers for as long as they tower over everything else.
So, sit back and get ready to tour the world's tallest peaks by satellite. No risk of avalanche. No threat of frostbite. No climbing boots required.
(NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team, archived on the USGS Earth Explorer.)
The shortest and youngest of the eight-thousand-meter peaks, Shisha Pangma is the only one located entirely within Tibet. (Of the others, three are entirely in Nepal and one in Pakistan. The rest sit along political borders.)
Though known today as one of easiest to climb, Shisha Pangma was the last eight-thousander summited due to restrictions on foreign travelers. A Chinese team reached the top in 1964, choosing a route that brought climbers up the northwest face along the northeast ridge. In the image above, much of the northwest face is cast in shadow. The steep, craggy south face--much more difficult to climb--rises more than 2,000 meters and has many areas with exposed rock.
According to statistics compiled by Eberhard Jurgalski, co-author of On Top of the World: The New Millennium, there had been 302 successful ascents of Shisha Pangma as of March 2012. Twenty-five people had died trying to climb the mountain--a fatality rate of about 8 percent. Many climbers finish on the Central Summit instead of continuing to the slightly higher Main Summit, which requires about an extra hour of climbing along a narrow ridge. British mountaineer Alex MacIntyre described the view along the ridge: "The ridge grew increasingly narrow and sharp. The north side was powdery and steep, impractical and dangerous to traverse; the south side was steeper, vanishing immediately into a jumble of rock and sugary ice."
(NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team, archived on the USGS Earth Explorer.)
The four Gasherbrum peaks are the highest points along an enormous horseshoe-shaped ridge on the border of Pakistan and China. The ridge encircles South Gasherbrum Glacier, a bowl-shaped mass of ice that flows into Baltoro Glacier, the longest glacier in the Karakoram (62 kilometers, or 39 miles). Gasherbrum II, the thirteenth tallest mountain in the world and the second tallest in the Gasherbrum group, is on the northernmost section of the ridge and about 10 kilometers (6 miles) southeast of K2--the tallest mountain in the Karakorum.
An Austrian team was the first to reach Gasherbrum II's summit, following a route up the south face along the southwest ridge in 1956. The Austrian team pioneered a new approach to climbing. During the ascent, night overtook the climbers at about 7,500 meters (24,600 feet). Rather than turning back to camp, they spent the night huddled near a cliff with no gear other than what they were carrying--a technique known as bivouacking. It was the first time a team deliberately bivouacked the night before attempting to summit an eight-thousander.
Today, Gasherbrum II is considered one of the safest and easiest eight-thousanders to climb. Over the years, climbers have skied, snowboarded, parachuted, and even hang-glided down from the summit. There had been more than 930 successful ascents of Gasherbrum II as of 2012, while only 21 people had died trying--a fatality rate of about 2 percent, the second lowest for the 8,000 meter peaks.
(NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team, archived on the USGS Earth Explorer.)
Located on the border of Pakistan and China, just a few kilometers southeast of K2, Broad Peak is the twelfth tallest mountain on Earth and the third tallest in the Karakoram Range. Its name comes from its unusually long summit ridge, which extends for about 2 kilometers. There is a snow-filled, saddle-shaped low point--or col--that separates the main summit from another high point to the north known as the central summit, which is just 31 meters (102 feet) shorter (8,016 meters versus 8,047 meters).
There is some discussion within the climbing community about whether the central summit deserves recognition as the 15th eight-thousander. Peaks in the Karakoram are only considered independent mountains if at least 500 meters of topographic prominence separates them from neighboring high points. If not, they are considered subsidiary peaks. While Broad Peak's central summit doesn't have enough prominence to be considered its own mountain, geographers think this could change in the future if the snow and ice that has collected in the col retreats enough.
An Austrian team was the first to climb Broad Peak, following a route up the southwest face in 1957. The team took no bottled oxygen and carried all of their own equipment rather than relying on porters. There had been a total of 404 successful ascents of Broad Peak as of March 2012, while 21 climbers had died trying--a fatality rate of about 5 percent.
Known until recently as Hidden Peak, Gasherbrum I is the eleventh tallest mountain on Earth. It is situated along the same horseshoe-shaped ridge on theborder of Pakistan and China as Gasherbrum II, though Gasherbrum I is 46 meters (151 feet) taller.
An American team made the first ascent in 1958, following a ridge on the southwest face. When Andy Kaufman and Pete Schoening reached the broad, snow-covered summit after battling through deep snow, they used small hand mirrors to signal their success to teammates at a camp below.
There had been a total of 334 successful ascents as of March 2012, while 29 climbers had died trying--a fatality rate of about 9 percent. Gasherbrum I is the only eight-thousander that Americans climbed first. Austrians, in contrast, were among the teams to ascend five of the eight-thousanders first. Nepalese climbers were the first teams up four of them. French teams were the first up two eight-thousanders. And Chinese, Japanese, Swiss, Italian, German, New Zealand climbers were all among the first to summit one of the eight-thousanders.
Annapurna is only the tenth tallest eight-thousander, but it ranks as one of the most dangerous. The mountain is located in Nepal along a 55-kilometer (34-mile) ridge just east of the Gandaki River, which has carved one of the deepest river gorges in the world. The gorge separates Annapurna from Dhaulagiri, the seventh tallest mountain in the world.
On June 3, 1950, the French climbers Maurice Herzog and Louis Lachenal reached the summit of Annapurna, making it the first eight-thousand meter peak ever successfully climbed. Herzog and Lachenal first attempted the northwest face--they called it the cauliflower face (shown in shadow in the image above)--then switched over to the avalanche-prone north face when they realized the northwest face was too rugged for their porters. The extremely steep south face, a wall of rock that rises 3,000 meters (9,800 feet), is said to be one of the most difficult climbs in the world.
Annapurna is the only 8,000 meter-peak to be conquered on the first try--and Herzog and Lachenal did it without bottled oxygen. However, the feat came with a high price. Since they wore only thin, leather boots up to the summit, the expedition's doctor had to amputate all of Herzog and Lachenal's toes after extreme frostbite and then gangrene set in during the descent. Herzog lost all of his fingers as well. Lachenal had asked Herzog during the summit climb: "Do you think it is worth it?" The rocks that make up Annapurna's summit--limestone formed at the bottom of a warm ocean--are a reminder of the powerful tectonic forces that pushed up the world's highest mountains. Other eight-thousanders with limestone near the summits include Everest and Dhaulagiri.
Only 191 people had successfully ascended Annapurna as of 2012, fewer than any other eight-thousanders. With a fatality rate of 32 percent, no other eight-thousander is deadlier.
Nanga Parbat is the ninth tallest mountain in the world, but it is one of the most alluring for both mountain climbers and scientists. Located in northern Pakistan, Nanga Parbat is the westernmost of the eight-thousanders. Despite being geographically close to the Karakoram, it actually represents the westernmost part of the Himalayan range.
Meaning "naked mountain" in Urdu, Nanga Parbat is a reference to the generally snow-free south face. Known as the Rupal face, this is the world's largest rock wall, rising some 4,700 meters (15,000 feet) from its base to the summit. The other faces--the Rakhiot face and the western Diamir--are also extreme. In the image above, the Rakhiot face is in shadow to the north, the Diamer face is to the east, and the Rupal face is to the south.
In the first-ever attempt to climb an eight-thousander, British mountaineer Albert Mummery ascended Nanga Parbat in 1895. Of the south face, he wrote: "The astounding difficulties of the southern face may be realized by the fact that the gigantic rock-ridges, the dangers of the hanging glacier and the steep ice of the north-west face--one of the most terrifying faces of a mountain I have ever seen--are preferable to the south face."
Mummery opted for the Diamir face instead, but disappeared, presumably killed by an avalanche. Subsequent expeditions fared no better, with an avalanche killing 16 men in a German team in the early 1900s and a storm killing another nine in 1934. Austrian Hermann Buhl was the first to make it to the summit, climbing solo and without oxygen in 1953. He followed a ridge on the Rakhiot face in what has gone down in mountaineering lore as one of the most remarkable climbs of all time. Just as notable as Nanga Parbat's climbing history is its geologic history. "There is no other mountain in the world that is rising as fast as Nanga Parbat," explained Mike Searle, a University of Oxford geologist.
As of March 2012, there had been a total of 335 successful ascents of Nanga Parbat. Sixty-eight had died trying--a fatality rate of about 20 percent, making it the third most dangerous eight-thousander.
Manaslu, the eighth tallest peak in the world, sits about 35 kilometers (22 miles) east of Annapurna in Nepal. While three long ridges lead up the mountain, the summit itself is a steep, sharp rock tower that can accommodate just a few people at a time.
Manaslu includes the usual risks that make climbing any eight-thousander a challenge: freezing weather, thin air, and avalanches. But a team of Japanese climbers exploring the area in 1954 faced a very different kind of obstacle: a mob of angry Nepalese armed with clubs, stones, and knives. The villagers, from nearby Sama, were enraged because they believed that a Japanese team that attempted to climb the mountain a year earlier had upset a god that lived on Manaslu's summit. They were convinced the deity had unleashed a destructive avalanche, as well as epidemics of smallpox and other diseases.
The 1954 team was forced to leave without attempting to climb the mountain. Mediation by the Nepalese government improved relations a bit, and another Japanese team arrived in 1956. This group followed a route up the mountain's northeast face, reaching the summit on a beautiful, windless day. It wasn't the only Japanese success on Manaslu. In 1974, an all-female team from Japan reached Manaslu's summit, the first women to successfully climb an 8,000-meter peak.
Manaslu remains one of the more dangerous eight-thousanders. As of March 2012, there had been 661 successful ascents of Manaslu; sixty-five climbers had died trying--a fatality rate of about 10 percent.
Known as the "White Mountain," Dhaulagiri is the seventh tallest mountain in the world. It is located in Nepal near Annapurna, with the two peaks separated by a deep gorge that was carved by the Gandaki River. Dhaulagiri rises abruptly from the surrounding terrain, soaring some 7,000 meters (2,300 feet) from the bed of the Gandaki.
Like Mount Everest, the summit of Dhaulagiri is geologically remarkable because it is comprised of limestone and dolomite rock layers that formed at the bottom of the ocean. Most of the other 8K peaks, in contrast, are composed of granites that formed deep underground.
In 1960, an international team of Austrian, German, Nepalese, and Swiss climbers reached the summit, following the northeastern ridge up the mountain's north face. There had been 448 successful ascents of Dhaulagiri as of March 2012, while 69 climbers had died trying--a fatality rate of about 16 percent.
Meaning "Goddess of Turquoise" in Tibetan, Cho Oyu is the sixth tallest mountain in the world. The massive peak is located on the border of Tibet and Nepal, approximately 20 kilometers (12 miles) west of Mount Everest.
Despite its size, Cho Oyu is considered the safest of the eight-thousanders because of the gentle slope of its northwestern face. There are few technically challenging areas on this face and avalanche risk is minimal. An Austrian team reached the summit via the northwestern face in 1953. Today, Cho Oyu is one of the most popular eight-thousanders. There had been 3,138 successful ascents as of March 2012, more than any other 8K peak except Everest. With a fatality rate of 1 percent, no other eight-thousander is safer.
"I experienced a wonderful feeling, as one step took me into another world," said Polish climber Jerzy Kukuczka, the second person to climb all 14 eight thousanders, upon reaching Cho Oyu's summit. "The steep walls and the knife-edge ridges vanished. It was as if I had stepped out of a dark and dangerous canyon onto a plateau bathed in purple light."
Makalu, the fifth tallest mountain in the world, is a pyramid-shaped mountain in Nepal, just 20 kilometers (12 miles) southeast of Mount Everest. There is a sharp difference--284 meters (932 feet)--between Makalu and Cho Oyu, the sixth tallest.
Makalu's classic pyramid shape is the product of bowl-shaped cirque glaciers grinding away at the summit on all sides. Erosion left thin ridges, known as aretes, which meet at the summit and form a shape that looks like an X from above.
In Tibetan, Makalu means "Great Black"--a reference to the oft-exposed granite that makes up the mountain's summit. The isolated peak is known for the strong winds that whip frequently around it and scour the snow away. The western and southern faces appear particularly bare in this image.
Makalu proved difficult to conquer. The southeast face thwarted an American team in 1954. A New Zealand team led by Edmund Hillary--the first person to ascend Mount Everest--failed the same year. A French team succeeded in 1955, following a route up the north face. Nine members of that team made it to the summit--an unusual accomplishment. During first ascents of most eight-thousanders, just one or two members of a team generally reached the summit, while others provided logistical support.
A total of 361 people had climbed Makalu successfully as of March 2012, while 31 had died trying--a fatality rate of about 9 percent.
Despite being the fourth tallest mountain in the world, Lhotse is often overshadowed by its taller neighbor Mount Everest, which lies just a few kilometers to the north. The two peaks are linked by the South Col, a vertical ridge that never drops below 8,000 meters.
Lhotse is 610 meters (2,000 feet) above the lowest point on the South Col--just enough for it to be considered an independent mountain. If Lhotse's topographic prominence were less than 500 meters, it would be considered a subsidiary peak of Everest.
Still, climbers often clump the two together. Lhotse is sometimes called Everest's South Peak. A Swiss team made the first ascent of Lhotse in 1956, tackling the mountain on the same expedition that they logged the second-ever ascent of Everest. They followed a route from the South Col up Lhotse's west face.
Far more challenging than getting to the summit of Lhotse is arriving via the south face. This requires ascending a 3,300-meter (11,000 foot) wall of rock that is vertical at times. It wasn't until 1990 that climbers ascended the south face successfully, a feat accomplished by a team from the former Soviet Union. A year before, Jerzy Kukuczka, the second person to climb all of the eight-thousanders, died trying to find a route up Lhotse's south face.
There had been a 461 successful ascents of Lhotse as of March 2012, while just 13 climbers died trying--a fatality rate of about 3 percent.
Kangchenjunga, the third tallest peak in the world, is the most easterly of the eight-thousanders. Kangchenjunga is located on the border between Nepal and India, 120 kilometers (75 miles) southeast of Mount Everest.
The structure of the mountain resembles a tent with four ridges radiating outward. The main and south summits are connected by a jagged north-south ridge that includes other high points well over 8,000 meters, though none have enough topographic prominence to qualify as separate peaks. There is no easy route up the steep, avalanche-prone slopes of Kangchenjunga. British climbers Joe Brown and George Band made the first ascent in 1955, following a route near the Yarlung Glacier to the foot of the mountain's southwest face. The local Sikkam people believed that a god lived at summit and told the climbers not to go all the way to the top (to avoid upsetting him). In deference to this, the British team turned back a few feet short of the true summit. There were 283 successful ascents of Kangchenjunga as of March 2012, the second fewest of the eight thousanders. (Annapurna is the only peak with fewer successful ascents.) Meanwhile, 40 people died trying to climb Kangchenjunga--a fatality rate of about 15 percent. Kangchenjunga was the last eight-thousander to be climbed by a woman; British climber Ginette Harrison made it in May 1998.
(NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team, archived on the USGS Earth Explorer.) Located on the border of Pakistan and China, K2 is the jewel of the Karakoram Range. The tallest mountain in the Karakoram and the second tallest in the world, K2 is just a few hundred meters shorter than Mount Everest.
K2's unusual name originated with a 19th century surveying project led by George Everest--the Great Trigonometrical Survey--that mapped and measured many of the highest peaks. Surveyors simply catalogued the peaks by number, giving each the prefix K for Karakoram followed by the number peak it was. K2 was the second mountain they came across. What the surveyors called K1, another peak in the area, was later changed to Masherbrum, the name used by local people. In the case of K2, there was no widely used local name, so the alphanumeric name stuck.
K2's modern nickname is "Savage Mountain" because of the extreme risks it poses to climbers--frequent avalanches and harsh weather. The Italian Duke of Abruzzi led an expedition up the southeast face in 1909 but gave up at about 6,250 meters (20,505 feet), believing it was not possible to climb K2. After many other failures, another Italian team eventually succeeded, following a route up southeastern ridge on the southwestern face in 1954.
There had been 306 successful ascents of K2 as of March 2012, the third fewest of the 8K peaks. Eighty-one people had died trying to climb the mountain--a fatality rate of about 29 percent, the second highest of the eight-thousanders.
Almost all who encounter Everest are awed by it. As the tallest mountain in the world, Everest is the standard to which all other mountains are compared. In Tibetan, the mountain is called Chomolungma, meaning "goddess mother of the snows." The Nepalese name is Sagarmatha, "mother of the universe."
Glaciers have chiseled Mount Everest's summit into a huge, triangular pyramid defined by three faces and three ridges that extend to the northeast, southeast, and northwest. The southeastern ridge is the most widely used climbing route. It is the route that Edmund Hillary and Tenzing Norgay followed in May 1953 when they became the first climbers to reach the summit and return safely.
Climbers who follow this route begin by trekking past Khumbu glacier and through the Khumbu ice fall, an extremely dangerous area where ice tumbles off the mountain into a chaotic waterfall of ice towers and crevasses. Next, climbers reach a bowl-shaped valley--a cirque--called the Western Cwm (pronounced coom) to the foot of the Lhotse Face, a 1,125-meter (3,691-foot) wall of ice. Climbing up the Lhotse face leads to the South Col, the low point in the ridge that connects Everest to Lhotse. It is from the South Col that most expeditions launch their final assault on the summit, following a route up the southeastern ridge.
Some climbers opt for the northern ridge, which is known for having harsher winds and colder temperatures. The northern ridge is the path that British climbers George Mallory and Andrew Irvine used in 1924 during what may, in fact, have been the first ascent. Whether the pair made it to the summit remains a topic of controversy, but what is known for certain is that the men were spotted pushing toward the summit just before the arrival of a storm. Mallory's corpse was discovered near the northeast ridge at 8,160 meters (26,772 feet) by an American climber in 1999, but it still isn't clear whether he reached the summit.
Despite its reputation as an extremely dangerous mountain, commercial guiding has done much to tame Everest in the last few decades. As of March 2012, there had been 5,656 successful ascents of Everest, while 223 people had died--a fatality rate of just 4 percent.
1. About.com The 8,000 Meter Peaks. The World's Highest Mountains. Accessed October 25, 2013.
2. Dech, S., Messner, R., Glaser, R. and Martin, R. (2005) Mountains from Space (New York: Harry N. Abrams, Inc.)
3. Economist (2012, May 29) Stairway to Heaven. Accessed October 25, 2013.
4. Gizmodo (2011, February 2) The Open Graveyard on Mt. Everest's "Death Zone."" Accessed October 25, 2013.
5. GlacierWorks (2013) Everest Tour.
6. Jurgalski, E. (2013) The 8000ers. Accessed October 9, 2013.
7. Messner, R. (1999) All 14 Eight-Thousanders (Seattle: The Mountaineers)
8. Peakbagger (2013) 8,000 meter peaks. Accessed October 9, 2013.
9. Sale, R. and Cleare, J. (2000) Climbing the World's 14 Highest Mountains (Seattle: The Mountaineers)
10. Sale, R., Jurgalski, E., and Rodway, G. (2012) On Top of the World: The New Millennium (Gloucestershire: Snowfinch Publishing)
11. Searle, M. (2013) Colliding Continents: A Geological Exploration of the Himalaya, Karakoram, and Tibet (New York: Oxford University Press)
12. U.S. Geological Survey The Himalayas: Two continents collide. Accessed November 27, 2013.
13. Weather Underground (2011, May 21) Extreme Weather of the Summit of Mt. Everest. Accessed October 9, 2013.