Mauna Loa is one of five volcanoes that form the
Island of HawaiiThe Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
in the
U.S. stateA U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
of
HawaiiHawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
in the Pacific Ocean, and the largest on
EarthEarth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
in terms of volume and area covered. It is an active
shield volcanoA shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
, with a volume estimated at approximately 18000 cubic miles (75,027.3 km³), although its peak is about 120 feet (37 m) lower than that of its neighbor,
Mauna KeaMauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
. The Hawaiian name "Mauna Loa" means "Long Mountain". Lava eruptions from Mauna Loa are silica-poor, and very fluid; eruptions tend to be
non-explosiveA Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high...
and the volcano has relatively shallow slopes.
Mauna Loa has probably been erupting for at least 700,000 years, and may have emerged above sea level about 400,000 years ago. The oldest-known dated rocks are not older than 200,000 years. The volcano's
magmaMagma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
comes from the
Hawaii hotspotThe Hawaii hotspot is the volcanic hotspot that created the Hawaiian Islands in the central Pacific Ocean, and is one of Earth's best-known and most heavily-studied hotspots....
, which has been responsible for the creation of the
Hawaiian island chainThe Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
over tens of millions of years. The slow drift of the
Pacific PlateThe Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
will eventually carry Mauna Loa away from the hotspot within 500,000 to one million years from now, at which point it will become extinct.
Mauna Loa's most recent eruption occurred from March 24, 1984, through April 15, 1984. No recent eruptions of the volcano have caused fatalities, but eruptions in 1926 and 1950 destroyed villages, and the city of Hilo is partly built on lava flows from the late 19th century. In view of the hazards it poses to population centers, Mauna Loa is part of the
Decade VolcanoesThe Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas...
program, which encourages studies of the most dangerous volcanoes. Mauna Loa has been intensively monitored by the
Hawaiian Volcano ObservatoryThe Hawaiian Volcano Observatory is a volcano observatory located at Uwekahuna Bluff on the rim of Kīlauea Caldera on the Island of Hawaii. The observatory monitors four active Hawaiian volcanoes: Kīlauea, Mauna Loa, Hualālai, and Haleakalā...
since 1912. Observations of the
atmosphereAn atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
are undertaken at the
Mauna Loa ObservatoryThe Mauna Loa Observatory is an atmospheric baseline station on Mauna Loa volcano, on the big island of Hawaii.-The observatory:Since 1956 Mauna Loa Observatory has been monitoring and collecting data relating to atmospheric change, and is known especially for the continuous monitoring of...
, and of the
SunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
at the
Mauna Loa Solar ObservatoryThe Mauna Loa Solar Observatory is a collection of instruments for observing the sun located on the slopes of the Mauna Loa volcano on the island of Hawaii, USA at an elevation of .-General information:...
, both located near its summit.
Hawaii Volcanoes National ParkHawaii Volcanoes National Park, established in 1916, is a United States National Park located in the U.S. State of Hawaii on the island of Hawaii. It encompasses two active volcanoes: Kīlauea, one of the world's most active volcanoes, and Mauna Loa, the world's most massive volcano...
covers the summit and the southeastern flank of the volcano, including a separate volcano,
KīlaueaKīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
.
Structure
Mauna Loa is the world's largest
shield volcanoA shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
in terms of area covered. Mauna Loa is shaped like a shield, because its lava is extremely
fluidIn physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
(it has low
viscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
), and its slopes are not steep. Eruptions are rarely violent, and the most common form is in the
Hawaiian styleA Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high...
, which involves
lava fountainA lava fountain is a volcanic phenomenon in which lava is forcefully but non-explosively ejected from a crater, vent, or fissure. Lava fountains may reach heights of up to . They may occur as a series of short pulses, or a continuous jet of lava. They are commonly seen in Hawaiian eruptions.-See...
s feeding lava flows. Typically, at the start of an eruption, a
riftIn geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
up to several kilometers long opens, with lava fountains occurring along its length in a so-called "curtain of fire." After a few days, activity normally becomes concentrated at one vent.
Eruptions generally occur in three regions on the mountain: at the summit and in two
rift zoneA rift zone is a feature of some volcanoes, especially the shield volcanoes of Hawaii, in which a linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit...
s extending northeast and southwest of the summit. About 38% of eruptions in the last two hundred years have occurred at the summit, 31% in the northeast rift zone, and 25% in the southwest rift zone. The remaining 6% have occurred from vents to the northwest of the summit, away from the rift zones. Its summit
calderaA caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
is called
Mokuāweoweo; it is 1.75 to 3 miles (3–5 km) in diameter. The caldera probably formed 1,000–1,500 years ago when a very large eruption from the northeast rift zone emptied out the shallow
magma chamberA magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...
beneath the summit, which then collapsed.
SeismicSeismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...
data can reveal the locations of the magma chambers beneath the volcano which feed activity. Some types of
seismic waveSeismic waves are waves of energy that travel through the earth, and are a result of an earthquake, explosion, or a volcano that imparts low-frequency acoustic energy. Many other natural and anthropogenic sources create low amplitude waves commonly referred to as ambient vibrations. Seismic waves...
s, known as "
S-waveA type of seismic wave, the S-wave, secondary wave, or shear wave is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves....
s," cannot travel through liquid rock, so magma chambers cast 'shadows' in seismic data. Seismic shadows reveal a magma chamber about 1.75 miles (3 km) beneath the summit and smaller magma bodies beneath the rift zones.
Trade windThe trade winds are the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth's atmosphere, in the lower section of the troposphere near the Earth's equator...
s blow from east to west across the Hawaiian islands, and the presence of Mauna Loa strongly affects the local climate. At low elevations, the eastern (windward) side of the volcano receives heavy rain, and the city of Hilo is the wettest in the United States. The rainfall supports extensive
forestA forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
ation. The western (leeward) side has a much drier climate. At higher elevations, the amount of precipitation decreases, and skies are very often clear. Very low temperatures mean that precipitation often occurs in the form of snow, and the summit of Mauna Loa is described as a
periglacialPeriglacial is an adjective originally referring to places in the edges of glacial areas, but it has later been widely used in geomorphology to describe any place where geomorphic processes related to freezing of water occur...
region, where freezing and thawing play a significant role in shaping the landscape.
Mokuāweoweo
Mokuāweoweo is the summit crater (
calderaA caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
) of Mauna Loa. Although a trail was developed in ancient times, Mokuaweoweo proved a difficult goal for the first outsiders who underestimated the difficulty of the journey. An American visit in 1840 turned into a trip of almost a month. Historically very active, Mokuāweoweo has been quiet since 1984.
The name of the summit crater is derived from the
āweoweo, a red Hawaiian big-eyed fish,
Priacanthus meekiPriacanthus meeki is a red fish found in Hawaiian and Midway Islands. It occasionally makes its way into the aquarium trade. It grows to a size of 33 cm in length. Common names are Hawaiian bigeye in English and āweoweo in the Hawaiian language...
, purportedly due to resemblance of the eruptive fires to the color of the fish. The main oval depression is about 3 miles (4,828 m) long and 1.5 miles (2,414 m) wide.
Two side craters, partially fused with the main one, are known as North Pit and South Pit. Southwest of the summit caldera are two smaller pit craters,
Lua Hou (New Pit) and
Lua Hohonu (Deep Pit).
Mokuāweoweo is now part of the
Hawaii Volcanoes WildernessHawaii Volcanoes Wilderness is a designated wilderness area within Hawaii Volcanoes National Park on the island of Hawaii in the U.S. state of Hawaii. It was designated in 1978 with , and was later expanded to . Wilderness designation covers the northwestern extension of the National Park,...
area, in the U.S.
National Wilderness Preservation SystemThe National Wilderness Preservation System of the United States protects federally managed land areas designated for preservation in their natural condition. It was established by the Wilderness Act upon the signature of President Lyndon B. Johnson on September 3, 1964...
.
Origins
Mauna Loa began erupting between 700,000 and 1,000,000 years ago and has grown steadily since then. Like all of the
Hawaiian islandsThe Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
, Mauna Loa has its origins in the
Hawaii hotspotThe Hawaii hotspot is the volcanic hotspot that created the Hawaiian Islands in the central Pacific Ocean, and is one of Earth's best-known and most heavily-studied hotspots....
—a plume of magma rising from deep in the Earth's
mantleThe mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
. The hotspot remains in a fixed position, while the
Pacific PlateThe Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
drifts over it at a rate of about 4 inches (10 cm) per year. The upwelling of the hot magma creates volcanoes, and each individual volcano erupts for a few million years before the movement of the plate carries it away from the rising magma.
The hotspot has existed for at least 80 million years, and the Emperor Seamounts chain of old volcanoes stretches almost 3600 miles (5,793.6 km) away from the hotspot. Currently, the hotspot feeds activity at five volcanoes: Mauna Loa,
KīlaueaKīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
, and
HualālaiHualālai is a dormant shield volcano on the island of Hawaii in the Hawaiian Islands. It is the third-youngest and the third most active of the five volcanoes that form the island of Hawaii, following Kīlauea and the much larger Mauna Loa, and also the westernmost. Its peak is above sea...
on the Big Island,
HaleakalāHaleakalā , or the East Maui Volcano, is a massive shield volcano that forms more than 75% of the Hawaiian Island of Maui. The western 25% of the island is formed by the West Maui Mountains.- History :...
on
MauiThe island of Maui is the second-largest of the Hawaiian Islands at and is the 17th largest island in the United States. Maui is part of the state of Hawaii and is the largest of Maui County's four islands, bigger than Lānai, Kahoolawe, and Molokai. In 2010, Maui had a population of 144,444,...
, and Loihi, a submarine volcano south of the Big Island and the youngest Hawaiian volcano. Mauna Loa is the largest of these, although Kīlauea is currently the site of the most intense volcanic activity.
Prehistoric eruptions
Prehistoric eruptions of Mauna Loa have been extensively analyzed by carrying out
radiocarbon datingRadiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...
on fragments of
charcoalCharcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
found beneath lava flows. The mountain's prehistoric activity is probably the best known of any volcano. Studies have shown that a cycle occurs in which volcanic activity at the summit is dominant for several hundred years, after which activity shifts to the rift zones for several more centuries, and then back to the summit again. Two cycles have been clearly identified, each lasting 1,500–2,000 years. This cyclical behavior is unique to Mauna Loa among the Hawaiian volcanoes.
Records show that between about 7,000 and 6,000 years ago Mauna Loa was largely inactive. The cause of this cessation in activity is not known, and no known similar hiatus has been found at other Hawaiian volcanoes except for those currently in the post-shield stage. Between 11,000 and 8,000 years ago, activity was more intense than it is today. However, Mauna Loa's overall rate of growth has probably begun to slow over the last 100,000 years, and the volcano may in fact be nearing the end of its
tholeiitic basaltThe tholeiitic magma series is one of two main magma series in igneous rocks, the other magma series being the calc–alkaline. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...
shield-building phase.
Climate
Mauna Loa has a tropical highland climate with cool to cold temperatures all year long. Below is the table for the slope obsevatory , not for the peak. The highest recorded temperature was 85F (29.4C) and the lowest was 18F (-7.7C) on February 18, 2003 and February 20, 1962, respectively.
Prehistoric
The
Ainapō TrailThe Ainapo Trail was the primary route to the summit of Mauna Loa from prehistory to 1916. The trail began on the southeast flank at 2000 feet of elevation and reached Mokuaweoweo, the summit crater, at...
was established in prehistoric times, rising from the village of Kapāpala over 11200 feet (3,413.8 m) in about 35 miles (56.3 km). Although the more active and accessible
KīlaueaKīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
caldera was the usual site to honor the fire goddess Pele, offerings and prayers were also made on Mokuāweoweo during its eruptions. Journeys up the trail extended over many days and required many porters. Several established camps along the way supplied water and food.
John Ledyard
John LedyardJohn Ledyard was an American explorer and adventurer.-Early life:Ledyard was born in Groton, Connecticut, the oldest son of John and Abigail Ledyard and the nephew of Continental Army Colonel William Ledyard...
led a team to attempt an ascent on the third voyage of Captain
James CookCaptain James Cook, FRS, RN was a British explorer, navigator and cartographer who ultimately rose to the rank of captain in the Royal Navy...
in January 1779. They struggled to go directly up from
Kealakekua BayKealakekua Bay is located on the Kona coast of the island of Hawaii about south of Kailua-Kona.Settled over a thousand years ago, the surrounding area contains many archeological and historical sites such as religious temples, and was listed in the National Register of Historic Places listings on...
, but turned back after an estimated 24 miles (38.6 km), thinking they had about 11 miles (17.7 km) more to go.
The summit was actually only a total of 20 miles (32.2 km) from the coast.
Archibald Menzies
Archibald MenziesArchibald Menzies was a Scottish surgeon, botanist and naturalist.- Life and career :Menzies was born at Easter Stix in the parish of Weem, in Perthshire. While working with his elder brother William at the Royal Botanic Gardens, he drew the attention of Dr John Hope, professor of botany at...
led a party from the
Vancouver ExpeditionThe Vancouver Expedition was a four-and-a-half-year voyage of exploration and diplomacy, commanded by Captain George Vancouver. The expedition circumnavigated the globe, touched five continents and changed the course of history for the indigenous nations and several European empires and their...
in the first successful ascent to Mokuāweoweo with a written record. He also first tried a direct route from the west and turned back in February 1793. After arriving again the next year, he climbed to the summit of
HualālaiHualālai is a dormant shield volcano on the island of Hawaii in the Hawaiian Islands. It is the third-youngest and the third most active of the five volcanoes that form the island of Hawaii, following Kīlauea and the much larger Mauna Loa, and also the westernmost. Its peak is above sea...
, on the northwest part of the island. He then tried to cross the interior plateau to Mauna Loa, but had to turn back. He consulted King
Kamehameha IKamehameha I , also known as Kamehameha the Great, conquered the Hawaiian Islands and formally established the Kingdom of Hawaii in 1810. By developing alliances with the major Pacific colonial powers, Kamehameha preserved Hawaii's independence under his rule...
and was astonished to learn he could take canoes to the south and follow the route established by
Ancient HawaiiAncient Hawaii refers to the period of Hawaiian human history preceding the unification of the Kingdom of Hawaii by Kamehameha the Great in 1810. After being first settled by Polynesian long-distance navigators sometime between AD 300–800, a unique culture developed. Diversified agroforestry and...
ans known as the Ainapō Trail.
On his third attempt on February 16, 1794, Menzies reached the summit and used a barometer to estimate the height as 13634 feet (4,155.6 m) compared to its currently known height of 13679 feet (4,169.4 m). He was surprised to find heavy snow and morning temperatures of 26 °F (-3.3 °C). He again underestimated the length of the climb and exhausted food rations, arriving with only three coconuts left for the summit party. The sheer mass of Mauna Loa is deceptive. Slopes are generally not very steep (always less than 12°) which makes it very hard to judge progress on the trail.
Others
On January 29, 1834, 40 years later, another European,
David DouglasDavid Douglas was a Scottish botanist. He worked as a gardener, and explored the Scottish Highlands, North America, and Hawaii, where he died.-Early life:...
, reached the summit, also using the Ainapō Trail.
It is sometimes reported that missionary Joseph Goodrich reached the summit around this time, but he never claimed this himself. He climbed Mauna Kea, and described the sight of Mokuāweoweo from Mauna Kea through a telescope.
Isidor Löwenstern successfully climbed Mauna Loa in February 1839, only the third successful climb in 60 years.
Wilkes expedition
The
United States Exploring ExpeditionThe United States Exploring Expedition was an exploring and surveying expedition of the Pacific Ocean and surrounding lands conducted by the United States from 1838 to 1842. The original appointed commanding officer was Commodore Thomas ap Catesby Jones. The voyage was authorized by Congress in...
led by Lieutenant
Charles WilkesCharles Wilkes was an American naval officer and explorer. He led the United States Exploring Expedition, 1838-1842 and commanded the ship in the Trent Affair during the American Civil War...
was tasked with a vast survey of the Pacific Ocean starting in 1838. In September 1840 they arrived in Honolulu, where repairs to the ships took longer than expected. He decided to spend the winter in Hawaii and take the opportunity to explore its volcanoes while waiting for better weather to continue the expedition. King
Kamehameha IIIKamehameha III was the King of Hawaii from 1825 to 1854. His full Hawaiian name was Keaweaweula Kiwalao Kauikeaouli Kaleiopapa and then lengthened to Keaweaweula Kiwalao Kauikeaouli Kaleiopapa Kalani Waiakua Kalanikau Iokikilo Kiwalao i ke kapu Kamehameha when he ascended the throne.Under his...
assigned American medical missionary Dr.
Gerrit P. JuddGerrit Parmele Judd was an American physician and missionary to the Kingdom of Hawaii who later became a trusted advisor and cabinet minister to King Kamehameha III.- Life :...
to the expedition as translator.
Wilkes sailed to Hilo on the
island of HawaiiThe Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
and decided to climb Mauna Loa first, since it looked easier than
Mauna KeaMauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
. On December 14 he hired about 200 porters, but after he left he realized only about half the equipment had been taken, so had to hire more Hawaiians at higher pay. When they reached Kīlauea after two days, their guide Puhano headed off to the established Ainapō Trail. Wilkes did not want to head back downhill so he blazed his own way through dense forest directed by a compass. The Hawaiians were offended by the waste of sacred trees, which did not help morale. At about 6000 feet (1,828.8 m) elevation they established a camp called "Sunday Station" at the edge of the forest.
Two guides joined them at Sunday Station: Keaweehu, "the bird-catcher" and another whose Hawaiian name is not recorded, called "ragsdale". Although Wilkes thought he was almost to the summit, the guides knew they were less than half way up. Since there was no water at Sunday Station, porters had to be sent back ten miles (16 km) to a
lava tubeLava tubes are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like...
on Ainapō Trail which had a known supply. After an entire day replenishing stocks, they continued up to a second camp they called "Recruiting Station" at about 9000 feet (2,743.2 m) elevation. After another full day's hike they established "Flag Station" on December 22, and by this time were on the Ainapō Trail. Most of the porters were sent back down to get another load.
At the Flag Station Wilkes and his eight remaining men built a circular wall of lava rocks and covered the shelter with a canvas tent. A snowstorm was in progress and several suffered from
altitude sicknessAltitude sickness—also known as acute mountain sickness , altitude illness, hypobaropathy, or soroche—is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude...
. That night (December 23), the snow on the canvas roof caused it to collapse. At daylight some of the group went down the trail to retrieve firewood and the gear abandoned on the trail the day before. After another day's climb, nine men reached the rim of Mokuāweoweo. They could not find a way down its steep sides so chose a smooth place on the rim for the camp site, at coordinates 19°27′59"N 155°34′54"W. Their tent was pitched within 60 feet (18.3 m) of the crater's edge, secured by lava blocks.
The next morning they were unable to start a fire using friction due to the thin air at that altitude, and sent for matches. By this time, the naval officers and Hawaiians could not agree on terms to continue hiring porters, so sailors and marines were ordered from the ships. Dr. Judd traveled between the summit and the Recruiting Station to tend the many who suffered from altitude sickness or had worn out their shoes on the rough rock. Christmas Day was spent building rock walls around the camp to give some protection from the high winds and blowing snow. It took another week to bring all the equipment to the summit, including a
pendulumA pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...
designed for measuring slight variations in gravity.
On December 31, 1840 the pre-fabricated pendulum house was assembled. Axes and chisels cut away the rock surface for the pendulum's base. It took another three days to adjust the clock to the point where the experiments could begin. However, the high winds made so much noise that the ticks could often not be heard, and varied the temperature to make measurements inaccurate. Grass had to be painstakingly brought from the lowest elevations for insulation to get accurate measurements.
On Monday, January 11, Wilkes hiked around the summit crater. Using an optical method, he estimated Mauna Kea was only 193 feet (58.8 m) higher (modern measurements are 104 feet (31.7 m) feet).
On January 13, 1841, he had "Pendulum Peak, January 1841 U.S. Ex, Ex." cut into a rock at the site.
The tents were dismantled and Hawaiians carried the gear down over the next three days, while Wilkes enjoyed a
lomilomiLomilomi, meaning "masseur, masseuse" in the Hawaiian language, is the word used today to describe Hawaiian massage, traditionally called lomi, meaning "to rub, press, squeeze, massage; to work in and out, as the claws of a contented cat"...
Hawaiian massage. He continued his measurements at lower elevations and left the island on March 5. For all the effort he did not obtain any significant results, attributing gravity discrepancies to "the tides".
The Wilkes expedition's camp site's ruins are the only known physical evidence in the Pacific of the U. S. Exploring Expedition. The camp site was listed on the
National Register of Historic PlacesThe National Register of Historic Places is the United States government's official list of districts, sites, buildings, structures, and objects deemed worthy of preservation...
on July 24, 1974 as site 74000295, and is state historic site 10-52-5507.
Today
A summit shelter was built with some of the stones from Wilkes' camp site and mortar in 1934. In 1916 Mokuāweoweo was included in
Hawaii Volcanoes National ParkHawaii Volcanoes National Park, established in 1916, is a United States National Park located in the U.S. State of Hawaii on the island of Hawaii. It encompasses two active volcanoes: Kīlauea, one of the world's most active volcanoes, and Mauna Loa, the world's most massive volcano...
, and a new trail was built directly from park headquarters at Kīlauea, an even more direct route than the one taken by Wilkes. This trail, arriving at the summit from the east via Red Hill, became the preferred route due to its easier access and gentler slope. After falling into disuse, the historic
Ainapō TrailThe Ainapo Trail was the primary route to the summit of Mauna Loa from prehistory to 1916. The trail began on the southeast flank at 2000 feet of elevation and reached Mokuaweoweo, the summit crater, at...
was reopened in the 1990s. A third modern route to the summit is from the Saddle Road, up to the
Mauna Loa ObservatoryThe Mauna Loa Observatory is an atmospheric baseline station on Mauna Loa volcano, on the big island of Hawaii.-The observatory:Since 1956 Mauna Loa Observatory has been monitoring and collecting data relating to atmospheric change, and is known especially for the continuous monitoring of...
which is located at the elevation of 11135 feet (3,393.9 m) a few miles north of Mokuāweoweo, and the North Pit trail.
Historic eruptions
Although
Ancient HawaiiAncient Hawaii refers to the period of Hawaiian human history preceding the unification of the Kingdom of Hawaii by Kamehameha the Great in 1810. After being first settled by Polynesian long-distance navigators sometime between AD 300–800, a unique culture developed. Diversified agroforestry and...
ans had witnessed eruptions for many centuries, written records exist only for eruptions that have occurred since the early 19th century. The first historical eruption occurred in 1832, and since then 32 eruptions have been documented.
The typical pattern is for an eruption to start at Mokuāweoweo, then move to a focal vent lower on one of the rift zones. Often, a major rift eruption is preceded by a smaller event that is limited to Mokuāweoweo, a year or more before the larger one. The latter occurred in 1880, 1940, and 1949, before the massive flank eruptions of 1881, 1942, and 1950. In total, these eruptions have covered over 310 square miles (802.9 km²) of the volcano's flanks with lava flows. Typically, eruptions have been brief but intense, with 0.06 to 0.12 cubic miles (0.25–0.5 km³) of lava erupted over a few weeks.
The most prominent historic eruptions of Mauna Loa, with extensive lava flows in forest and agricultural areas, were in 1855, 1881, 1935, 1942, and 1950 on the northeast rift zone; 1887, 1907, 1916, 1919, 1926, and 1950 on the southwest rift zone; and the 1859 radial vent eruption.
An eruption in 1935 that headed toward the city of Hilo led to an unusual employment of air power. Five bombers of the 23d and 72d Bombardment Squadrons of the United States Air Force dropped bombs in the path of the lava in order to divert it away from Hilo. The eruption stopped six days later. Fissures opened to the northwest and southeast, from the summit down to 9500 feet (2,895.6 m) above
sea levelMean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
. Flows from this eruption headed rapidly towards Hilo again, but stopped about 2.5 miles (4 km) from the outskirts when the eruption ended after three weeks.
As of 2009, Mauna Loa has been inactive for over 25 years, its longest quiet period in recorded history.
Current activity
In 2002
seismic activityAn earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
, which had been low, increased, and inflation suddenly started, and the caldera walls started to move apart at 2 inches (5 cm) per year. This is thought to indicate that magma is filling a reservoir about 3.1 miles (5 km) beneath the summit. The inflation has been intermittent, sometimes slowing, and sometimes stopping for several weeks. Thus far, though, it has always restarted, and this is likely to indicate an increased probability of an eruption in the next few years.
In July 2004 a swarm of deep earthquakes began, and continued until the end of the year. Earthquakes were detected at a rate of one per day for the first three weeks, increasing steadily over subsequent months to 15 or so per day by the end of the year. The swarm ended in December 2004, and earthquake levels have been only moderately elevated since then.
Relationship with Kīlauea
KīlaueaKīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
lies on the southern flank of Mauna Loa and was originally thought to be a satellite vent of Mauna Loa. However, chemical differences between the lavas from the two volcanoes show that they have separate shallow magma chambers. They are now considered separate volcanoes. Nevertheless, activity patterns at the two volcanoes do appear to be correlated.
The most apparent relation between the two mountains is that, generally, periods of frequent activity at one volcano coincide with periods of low activity at the other. For example, between 1934 and 1952, Kīlauea was dormant and only Mauna Loa was active, while from 1952 to 1974, only Kīlauea was active while Mauna Loa lay dormant.
The 1984 eruption of Mauna Loa started during an eruption at Kīlauea, but had no discernible effect on the Kīlauea eruption. Occasionally, though, eruptions at one volcano do seem to influence activity at the other. The recent inflation of Mauna Loa's summit began on the same day as a new large lava flow broke out at Kīlauea's Puu Ōō crater. Geologists have suggested that a "pulse" of magma entering Mauna Loa's deep plumbing system could have increased pressure inside Kīlauea and triggered the eruption.
Hazards
Volcanic eruptions in Hawaii rarely cause casualties: the only fatality due to volcanic activity there in the last century occurred at Kīlauea in 1924, when an unusually explosive eruption hurled rocks at onlookers, killing one. However, property damage is common. Mauna Loa is a Decade Volcano, which means it has been identified as worthy of particular research in light of its frequent eruptions and proximity to populated areas. Many towns and villages near the volcano are built on lava which has erupted in the last two hundred years, and there is a very strong likelihood that future eruptions will cause damage to populated areas.
Areas of the volcano have been classified into different Lava Flow Hazard Zones. There are two classifications. One classification is based upon historical flows and uses a 1-9 numbering system. The second classification was created to account for present flow activity and uses the numbers 11, 12 and 13.
Lava flows
The main volcanic hazard at Mauna Loa is lava flows. Most flows advance at about walking pace and present little danger to human life, but eruptions at Mauna Loa can be more intense than those at Kīlauea; for example, the 1984 eruption emitted as much lava in three weeks as Kīlauea's current eruption produces in three years. Such high emission rates can generate comparatively fast-moving flows.
Two eruptions of Mauna Loa have destroyed villages. In 1926, the village of Hoōpūloa Makai was overrun by lava flows. In 1950, the most voluminous eruption ever seen at Mauna Loa sent lava flows racing towards the sea. The village of Hookena Mauka was destroyed on June 2, 1950 by the advancing flows. Hilo is partly built on lava from the 1880-81 eruption and is at risk from further lava flows. The brief but intense 1984 eruption saw lava flow towards Hilo, but it had not reached any buildings when the eruption stopped.
Flank collapse
A rarer but potentially greater hazard at Mauna Loa is the possibility of a sudden massive collapse of the volcano's flanks. Deep faults allow large portions of the sides of Hawaiian mountains to slide gradually downwards, the best known example being the
Hilina SlumpThe Hilina Slump is a 5,000 cubic mile chunk of the big island of Hawaii on the south flank of the Kilauea volcano. Between 1990 and 1993, Global Positioning System measurements showed a southward displacement of the south flank of Kilauea up to approximately 10 centimeters per year...
. (There is also the more ancient example of the
Ninole HillsThe Ninole Hills, also known as the Ninole Volcanic Series, are steep, eroded hills known as shield basalts located on the south side of the Island of Hawaii...
.) Occasionally, a large earthquake can trigger a collapse of the flank, creating a massive
landslideA landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
which may trigger a
tsunamiA tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
.
Kealakekua BayKealakekua Bay is located on the Kona coast of the island of Hawaii about south of Kailua-Kona.Settled over a thousand years ago, the surrounding area contains many archeological and historical sites such as religious temples, and was listed in the National Register of Historic Places listings on...
, on the western slope of Mauna Loa, was created by such an event. Undersea surveying has revealed numerous landslides along the Hawaiian chain and two giant tsunamis are known to have occurred: 200,000 years ago,
MolokaiMolokai or Molokai is an island in the Hawaiian archipelago. It is 38 by 10 miles in size with a land area of , making it the fifth largest of the main Hawaiian Islands and the 27th largest island in the United States. It lies east of Oahu across the 25-mile wide Kaiwi Channel and north of...
experienced a 246-foot (75 m) tsunami, and 100,000 years ago a
megatsunamiMegatsunami is an informal term to describe a tsunami that has initial wave heights that are much larger than normal tsunamis...
1066 feet (325 m) high struck
LānaiLānai or Lanai is the sixth-largest of the Hawaiian Islands. It is also known as the Pineapple Island because of its past as an island-wide pineapple plantation. The only town is Lānai City, a small settlement....
.
A recent example of the risks associated with slumps occurred in 1975, when the Hilina Slump suddenly moved forward by several yards. A
magnitudeThe expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....
7.2 earthquake resulted which triggered a small
tsunamiA tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
with a wave height of a few yards, killing two campers at Halape.
Monitoring
Mauna Loa is an intensively monitored volcano. The
Hawaiian Volcano ObservatoryThe Hawaiian Volcano Observatory is a volcano observatory located at Uwekahuna Bluff on the rim of Kīlauea Caldera on the Island of Hawaii. The observatory monitors four active Hawaiian volcanoes: Kīlauea, Mauna Loa, Hualālai, and Haleakalā...
(HVO) was established in 1912 to observe the Hawaiian volcanoes, and the HVO has developed many techniques to help predict when eruptions at Mauna Loa and other volcanoes are imminent.
One of the most important tools is seismometry. More than 60
seismometerSeismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources...
s around the Big Island enable scientists to measure the intensities and locations of hundreds of small earthquakes every week. Earthquakes can begin to increase years before an eruption actually starts: The 1975 and 1984 eruptions were both preceded by one to two years of increased seismic activity at depths of less than 8 miles (13 km).
Another type of seismic activity occurs in the hours preceding an eruption. So-called
harmonic tremorHarmonic tremor describes a long-duration release of seismic energy, with distinct spectral lines, that often precedes or accompanies a volcanic eruption...
is a continuous "rumble" which contrasts with the normal seismic activity of sudden shocks and is believed to be caused by the rapid movement of magma underground. Volcanic tremor normally indicates an imminent eruption, although it may also be caused by shallow intrusions of magma which do not reach the surface.
Another important indicator of what is happening underground is the shape of the mountain.
TiltmeterA tiltmeter is an instrument designed to measure very small changes from the horizontal level, either on the ground or in structures. A similar term, in less common usage, is the inclinometer...
s measure very small changes in the profile of the mountain, and sensitive equipment measures distances between points on the mountain. As magma fills the shallow reservoirs below the summit and rift zones, the mountain inflates. A survey line across the caldera measured a 3-inch (76 mm) increase in its width over the year preceding the 1975 eruption and a similar increase before the 1984 eruption.
Observatories
The location of Mauna Loa has made it an important location for atmospheric monitoring by the
Global Atmosphere WatchThe Global Atmosphere Watch is a worldwide system established by the World Meteorological Organization a United Nations agency to monitor trends in the Earth's atmosphere...
and other scientific observations. The
Mauna Loa Solar ObservatoryThe Mauna Loa Solar Observatory is a collection of instruments for observing the sun located on the slopes of the Mauna Loa volcano on the island of Hawaii, USA at an elevation of .-General information:...
(MLSO), located at 11155 feet (3,400 m) on the northern slope of the mountain, has long been prominent in observations of the
SunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. The NOAA
Mauna Loa ObservatoryThe Mauna Loa Observatory is an atmospheric baseline station on Mauna Loa volcano, on the big island of Hawaii.-The observatory:Since 1956 Mauna Loa Observatory has been monitoring and collecting data relating to atmospheric change, and is known especially for the continuous monitoring of...
(MLO) is located close by. From its location well above local human-generated influences, the MLO monitors the global atmosphere, including the
greenhouse gasA greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
carbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. Measurements are adjusted to account for local degassing of CO
2 from the volcano.
Since October 2006, the Array for Microwave Background Anisotropy (AMIBA) has been exploring the origin of the universe.
The
Hawaiian Volcano ObservatoryThe Hawaiian Volcano Observatory is a volcano observatory located at Uwekahuna Bluff on the rim of Kīlauea Caldera on the Island of Hawaii. The observatory monitors four active Hawaiian volcanoes: Kīlauea, Mauna Loa, Hualālai, and Haleakalā...
maintains seismic sensors and a web cam on Mokuāweoweo.
See also
- Mountain peaks of the United States
This article comprises three sortable tables of the major mountain peaks of the United States of America.Topographic elevation is the vertical distance above the reference geoid, a precise mathematical model of the Earth's sea level as an equipotential gravitational surface...
- List of Ultras in Oceania
External links