The scientific party lost only one day because of the dynamite theft. Governor Montoya supplied more explosives and the firing schedule continued. Now, however, the dynamite was guarded by police supplied by His Excellency. Police also were in evidence around the Hot Springs Hotel. No more chances were being taken. After three days, the scientists began to have a better idea of what was going on in the earth beneath them, but Rick and Scotty could make little sense of the mass of data. Even the picture being filled in by Dr. Williams was confusing. Now, two magma areas were showing where only one had shown before. Esteben Balgos answered Rick's plea for an explanation. Over an excellent dinner of roast suckling pig and bananas steamed with lemon juice, the volcanologist took time to answer their questions. "There is much we do not know about volcanoes," the Peruvian scientist began. "For example, we do not know exactly what causes magma to form. Magma is, in simplest terms, molten rock. Some event takes place far below, where the earth's crust ends and the mantle begins, and the rock melts." "How far below?" Rick asked. "The distance varies. Under the ocean trenches, for example, the mantle may begin only four miles down. Under some of the mountainous land masses it may be closer to forty miles." Scotty whistled. "That's a whale of a distance. How can you tell how far down it is?" "By the seismic traces from earthquakes, or from explosive shots like the ones we are shooting. When the shock waves have reached the zone between the earth's crust and the mantle, we see the results on our tracings." "Is it really a sharp line?" Rick queried. "Probably not. No one is sure yet. It may be a kind of transitional zone, from one kind of material to another, or it may be a distinct layer. We call it the Mohorovicic Discontinuity, after the Yugoslav scientist who discovered it by analysis of seismic tracings. At any rate, it is somewhat above this discontinuity that magma is formed. We don't know how." "Then it rises?" Scotty asked. "It forces its way up, by expansion. Sometimes the magma strikes water and there is an explosion--a steam explosion. But generally the magma rises through a fairly small channel. It forms a pool under the volcano. The pool is actually a reservoir of molten rock. Generally it is shaped like a lens. The magma gathers. Eventually it forces its way to the surface, again through channels." "What kind of channels?" Rick asked. "It depends on the kind of volcano. Sometimes the channels are weaknesses in the whole surrounding earth structure, and the magma flows through cracks and emerges as sheets of lava. Sometimes there is a central channel through which the magma can rise." "Which do we have?" Scotty wanted to know.