page_title: Mauna Loa
section_title: Wilkes expedition
hierarchical_section_title: Mauna Loa / Human history / Wilkes expedition
caption_attribution_description: English: Wilkes Campsite — Illustration from Lt. Charles Wilkes journal of the U.S. Exploratory Expedition, January 1841 by ship artist Alfred Thomas Agate of their camp site at Mokuaweoweo, the summit of Mauna Loa.
context_page_description: Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaiʻi in the Pacific Ocean. The largest subaerial volcano in both mass and volume, Mauna Loa has historically been considered the largest volcano on Earth, dwarfed only by Tamu Massif. It is an active shield volcano with relatively gentle slopes, with a volume estimated at approximately 18,000 cubic miles, although its peak is about 125 feet lower than that of its neighbor, Mauna Kea. Lava eruptions from Mauna Loa are silica-poor and very fluid, and they tend to be non-explosive.
  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 magma comes from the Hawaii hotspot, which has been responsible for the creation of the Hawaiian island chain over tens of millions of years. The slow drift of the Pacific 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 to April 15, 1984.
context_section_description: The United States Exploring Expedition led by Lieutenant Charles Wilkes 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. Wilkes 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 III assigned American medical missionary Dr. Gerrit P. Judd to the expedition as a translator.
  Wilkes sailed to Hilo on the island of Hawaiʻi and decided to climb Mauna Loa first, since it looked easier than Mauna Kea. On December 14 he hired about 200 porters, but after he left he realized only about half the equipment had been taken, so he had to hire more Hawaiians at higher pay. When they reached Kīlauea after two days, their guide Puhano headed off to the established ʻAinapō 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 6,000 feet (1,800 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 halfway up. Since there was no water at Sunday Station, porters had to be sent back ten miles (16 km) to a lava tube on ʻAinapō 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 9,000 feet (2,700 m) elevation. After another full day's hike they established "Flag Station" on December 22, and by this time were on the ʻAinapō 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 sickness. 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 Mokuʻāweoweo. 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 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 pendulum 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 193 feet (59 m) higher, while modern measurements indicate a difference of about 125 feet (38 m). On January 13, 1841, he had "Pendulum Peak, January 184
caption: Sketch by ship's artist Alfred Thomas Agate
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