Drilling of lava lakes can be risky. When the Mauna Ulu eruption began on May 24, 1969, a lava flow poured into Alae Crater and quickly buried a drill rig and related equipment before they be could be lifted out by helicopter! A more common risk is posed by the occasional minor steam explosions in the drillholes caused by contact of cooling water with the molten lava. Fragmental volcanic products Fragmental volcanic debris is formed during mildly explosive activity, such as lava fountaining, and, less commonly, during the infrequent violently explosive eruptions, such as during 1790 at Kilauea. Tephra is the general term now used by volcanologists for airborne volcanic ejecta of any size. Historically, however, various terms have been used to describe ejecta of different sizes. Fragmental volcanic products between 0.1 to about 2.5 inches in diameter are called lapilli; material finer than 0.1 inch is called ash. Fragments larger than about 2.5 inches are called blocks if they were ejected in a solid state and volcanic bombs if ejected in semi-solid, or plastic, condition. In a major explosive eruption, most of the pyroclastic debris would consist of lapilli and ash. Volcanic bombs undergo widely varying degrees of aerodynamic shaping, depending on their fluidity, during the flight through the atmosphere. Based on their shapes after they hit the ground, bombs are variously described, in graphic terms, as "spindle or fusiform," "ribbon," "bread-crust," or "cow-dung."

Shiny strands of volcanic glass, called Pele's hair (above) are commonly found downwind from active eruptive vents. Volcanic spatter commonly becomes tightly welded to form mounds around active vents (below). (Photographs by Donald W. Peterson and Richard P. Moore, respectively.)

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Updated 05.01.97