At almost 14,000 feet, the summit of Mauna Kea has its own climate. Even summer months can bring snow, strong winds, storms, thick fog and hail.
The amount of snowfall varies from year to year. Snow often falls first and melts last on the northern slope of the cinder cone Pu‘u Hau Kea. At times it is the only place on the mountain with snow. Translated from the Hawaiian, Pu’u Hau Kea means “hill of white snow.”
Temperatures can vary thirty degrees between noon and night. It can reach up to 60 degrees Fahrenheit on a summer's day, and is often just above freezing in the winter. Winter or summer, nighttime temperatures are usually at freezing or below.
A tropical inversion cloud layer about 2,000 feet thick, sits well below the summit. It is this inversion layer that isolates the upper atmosphere from the moist maritime air at lower levels and ensures that the summit skies are dry and free from atmospheric pollutants.
The tops of Mauna Loa and Mauna Kea are much drier than the tops of many other high mountains. The inversion layer is very effective in keeping the moisture below. Hawai’i island has a significant orographic effect. Orographics is the effect of the terrain on weather.
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The hau is a wind from the mountains, and they are thought to be the cause of it, because this wind invariably blows from the mountains outwards towards the circumference of the island.
The high volcanoes of Hawaii have the capability of generating mammoth waves in the upper atmosphere. A sailplane pilot in 1969 surfed the skies above Mauna Kea, catching the mountain wave and riding it to 22,000 feet.
Violent turbulence can be encountered by aircraft, as anyone flying to and from the island of Hawai’i can testify. Mauna Kea, with its size and position, commands the winds, creating a wake that stretches for thousands of miles downwind, affecting ocean currents between Hawai`i and Asia.
See “Little Islands, Big Wake.”
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The very top of the summit, above the alpine zone, has been dubbed by scientists the Aeolian zone, named for the Greek god of winds. The mountain's strong forces can catch visitors by surprise. A snowboarder, standing on the ridge of one of the high cinder cones, was blown over by a wind gust and slid 1,500 feet down the side of an icy, 45-degree slope.
Winds are predominately from the west/northwest during the day and from the east/northeast at night at about 10 to 15 miles per hour. During severe winter storms, winds can exceed 100 miles per hour on exposed summit areas, such as the top of cinder cones.
–Draft EIS, Mauna Kea Science Reserve Master Plan
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Winds have reached hurricane velocities several times, gusting to 123 mph on Feb. 11, 1996.
The Light on White Mountain
–Honolulu magazine, May 1996
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The interaction of winds and mountains is well known in Maori culture.
When the wind blows up the valley from a particular quarter it may create a cloud formation high above the maunga. This is referred to as a potae or a hat. It is a tohu or symbol well known to the local iwi and may mean a number of things, death, a sign of impending danger, or the reverse, a sign of a change in the seasons, plentiful food, a seasonal change in harvesting and so on.
During certain rare weather and wind patterns, remarkable lenticular clouds sometimes appear over Mauna Kea.
The Maori of Aotearoa refer to this type of cloud as a potae or a hat, and report that it can be a sign of change, either good or bad.
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The air at the summit is thin. Visitors there are above half of the earth's atmosphere, breathing in only about half as much oxygen as at sea level. Those who have not acclimated themselves to the elevation often find themselves gasping for breath and sometimes suffering more serious symptoms of altitude sickness, resulting in headaches, nausea, and confusion; or pulmonary edema, a condition that causes extreme shortness of breath. Although supplemental oxygen can alleviate some of these symptoms, the only cure for severe cases is to return to lower elevations.
The background radiation at the summit is high.
The stark, volcanic landscape of the Mauna Kea summit may seem to be a biological desert. Whatever life is here must endure extreme conditions. But signs of life are to be found.
That place is amazingly cold at night, can get really hot during the day. You have this huge ultra-violet impact from the sun. It gets very wet sometimes when the big storms move through and freezing rains and mists are moving past. And so things up there have to be amazingly tough to be able to survive all of that.
–Sam ‘Ohukani’ohi’a Gon III
excerpt from Mauna Kea – Temple Under Siege
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The freeze thaw cycle
Daily cycles of freezing and thawing continue to affect the summit terrain today. The temperature falls below the freezing point every night in the year, and, with the possible exception of short periods during the winter, it rises above freezing point each day. Thus alternate melting and freezing of ice in cracks is nearly a continuous process.
Daytime melting of snow permits water to trickle down rock surfaces and into all accessible crevices, only to expand when frozen at night, splitting the rocks apart. Frost action is responsible for arranging the pockets of rock fragments into mosaic-like patterns. Observations indicate that the wedgework of ice on Mauna Kea is an exceptionally active process.
The process creates ever-changing patterns of rock fragments. The freeze/thaw process concentrates fine material on ridges and coarse material in grooves, producing stripes, geometrically regular alterations of stones and fine-grained ash the appear as rivulets on the sides of the cinder cones.
General Features and Glacial Geology of Mauna Kea, Hawaii
by Herbert Gregory and Chester Wentworth
Bulletin of the Geological Society of America
Vol. 48, 1937