Mauna Loa, the largest active volcano

eruption at Mauna Loa

  Mauna Loa (Long Mountain) lies to the south of Mauna Kea and, like it, rises from a plain 18,000 feet below sea level. Mauna Loa is 13,675 feet high; it is the largest active volcano in the world. Its dimensions are quite staggering; it is about sixty miles across and two hundred miles in circumference at sea level. At the summit there is a huge crater, which is called Mokuaweoweo. This crater is five miles in circumference; the cliffs around its pit are from 500 to 600 feet high. There is considerable volcanic activity in Mokua­weoweo, particularly before an eruption; white-hot fountains of lava rise to a height of several feet. However, there have been no flows of lava from this crater, at least in historie times. All the lava discharges from Mauna Loa come from the flanks of the mountain, at elevations of from 7,000 to 13,000 feet.

Some historic Mauna Loa lava flows
  There have been numerous eruptions in the past hundred years or so, at intervals of a few years. The eruption of 1873-74 lasted eighteen months; that of 1880-81, nine months. In 1926, a lava flow from a crevice in the southeastern side of the mountain destroyed the village of Hoopuloa, on the coast. This flow was thirty feet high, and advanced along a front of about a hundred feet at the rate of three feet a minute. Thomas A. Jaggar, director of the Hawaiian Volcano Observatory, compared the flow to the lumbering advance of a caterpillar tractor. Said he: "An upper layer of boulders and paste is rolled forward on a viscous red-hot paste inside, tumbles down at the front in a debris slope and this is eternally overridden by the advancing mass for which it lays the track."
  In 1935, the city of Hilo was threatened by a lava flow proceeding from the northwest flank of Mauna Loa. The United States Army Air Corps (it is now a sep­arate military arm) came to the rescue. A fleet of bombers dropped 6,000 pounds of bombs from a height of about 5,000 feet above the lava. The bursting bombs opened up new channels for the lava flow, diverted its course, and saved the city.