2007-05-23 03:27:08 · 4 answers · asked by Clarence C 2 in Science & Mathematics ➔ Earth Sciences & Geology
The pressure of the earth above it.
2007-05-23 03:32:56 · answer #1 · answered by Flyboy 6 · 0⤊ 1⤋
Magma by definition is molten rock (while it is below the earth's surface - it is called lava once it reaches the surface), and so "solid" magama is a contradicion in terms.
With the exception of the outer core, the earth is almost entirely solid, and contains virtually no maga. The rocks of the mantle (the layer above the core but below the crust) although very hot, are under extremly high pressure, and for the most part this intense pressure prevents them from melting. However, the rocks of the mantle (except the uppermost part) are sufficiently hot that over long periods they can deform and behave like a very viscous fluid and flow (hence plate tectonics). Where this flow brings the hot mantle rocks towards the surface, the drop in pressure can cause partial melting generating magma. Alternatively, introducing things such as water into hot rocks can also lower their melting point leading to the formation of magma.
2007-05-25 07:31:26 · answer #2 · answered by Andrew 5 · 0⤊ 0⤋
It is not magma. The mantle is composed of solid crystalline rock though at the temperatures and pressures there, it behaves plastically.
2007-05-23 05:11:29 · answer #3 · answered by JimZ 7 · 1⤊ 0⤋
Pressure. With enough pressure even water acts as a solid.
2007-05-23 03:36:39 · answer #4 · answered by verbalise 4 · 0⤊ 1⤋