Icelandic - Volcanic eruptions may be classified in order of increasing violence. Icelandic eruptions involve the quiet outpouring of lava from long fissures. Most than 2 1/2 cu mi of lava flowed from Iceland's Lake Fissure in 1783, the largest emission of lava in historic times. Eruptions of the Icelandic type during the Tertiary Period built up vast basalt plateaus in many parts of the World. One of the largest is the Columbia Plateau, more than 20,000 sq mi in the northwestern United States.
Hawaiian - Lava issues from a single vent in eruptions of the Hawaiian type. Each flow adds a layer of rock to a broad, gently sloping mountain called a shielt volcano. In calderas at their summits shield volcanoes may contain lava lakes in which lava continuosly circulates from below. The volcano Niragongo in Africa contains a lava lake, as did Kilauea in Hawaii. The escape of gas at the vent during Hawaiian erputions often produces lava fountains several hundred feet high.
Strombolian - Continuos eruptions that emit showeres of lava at rhythmic intervals are called strombolian after the volcano Stromboli, north of Sicily. Much of the erupted material is fragmental, so that the cone is steep sided. A cross section would show alternate layers of pyroclastic material and lava flows, forming a mountain known as a stratovolcano.
Vulcanian - In Vulcanian eruptions, which also produce stratovolcanoes, the magma is more acid and less fluid than in the preceding types. The opening phase is explosive, blowing away the thick crust over the vent and often destroying part of the mountain. Lava flows may emerge later. Both Vulcano, from which such eruptions are named, and Italy's Mount Vesuvius illustrate this type of activity. In 79 A.D. an eruption of Mount Vesuvius buried the city of Pompeli under a layer of pumice, and many of its 20,000 inhabitants were killed. A nearby city, Herculaneum, was buried by a lahar, or mudflow, caused by rains that accompanied the eruption. A single Vulcanian eruption where none has occurred before produces a cinder cone, or pyroclastic cone, surrounded by lava flows. Paricutin is an example.
Pelean - The most explosive eruption is the Pelean type, named for the 1902 eruption of Mount Pelee on the island of Martinique in the West Indies. On the morning of May 8 a blast of steam and red-hot ash shot laterally from the volcano and destroyed the city of Saint Pierre and all but two of more than 26,000 inhabitants. This was the greatest loss of life ever known to result directly from an eruption, although 80,000 lives were lost in the famine that was caused by the eruption in 1815 of Tambora in the East Indies. The blast that destroyed Saint Pierre was a nuee ardente, a stream of ash-laden gas that forced a passage through the viscous magma that clogged the crater. Some months later a volcanic spine, or tower of stiff lava, arose from the crater. It reached a height of 1,020 ft above the crater floor before collapsing.
Phreatic - Violent phreatic eruptions, similar to the Pelean type, are caused by the vaporization of underground water by magma. In the phreatic eruption of Bandai-san, in Japan, 461 persons lost their lives in 1888.