Igneous pumice rocks have a spongy appearance and low density.
When you’re on solid earth, it’s hard to think of the planet as anything other than very solid rock. This is still not the case. Several kilometers below the earth’s crust, hard rock is replaced by softer rock and, ultimately, liquid rock with gases and minerals, which occasionally arise from volcanoes or cracks in the earth.
You certainly wouldn’t want to be near this molten rock, as its temperature is extremely high. Although some materials melt at temperatures of around 1100 degrees F (593.33 C), most of the magma beneath the Earth’s crust maintains temperatures between 1292 and 2372 degrees F (700-1300 C). When molten rock erupts or flows to the Earth’s surface, it quickly loses heat energy, although it is still much hotter than the exposure would warrant.
The magma beneath the Earth’s crust is between 1292 and 2372 degrees Fahrenheit.
Some scientists make the distinction between magma and lava, defining lava as molten rock that is on or above the Earth’s surface. This can also be called extrusive. Another way to see traces of molten rock above the earth, in addition to lava flows, is by examining igneous rock. All igneous rocks are formed from magma, and some rocks resemble the liquid flow that produced them. Obsidian, for example, is shiny and brittle and in some ways resembles the flow of certain types of magma. It is actually a naturally occurring glass and gets its luster and smoothness from the fact that magma has not crystallized upon cooling.
Igneous rock is formed by magma.
Another interesting igneous rock created by molten rock is pumice, which is very light, so light that it will float in most fluids. Unlike the soft glow of obsidian, pumice stone resembles natural sponges, with various marks of pustules. They are caused when gases create bubbles in the rock, which doesn’t have time to form before it cools. This results in the appearance of bubbles in the pumice stone and its low density.
What creates magma? Temperature and pressure increase as you go deeper into the Earth’s layers. It’s comparable to the way things heat up when you put them in the microwave. The hottest part is always the center and the inside.
Under certain conditions, where the heat becomes extreme, some of the rock that forms under the crust begins to melt. As the heated rock rises, it begins to cool again, creating some of the igneous rocks that make up portions of the Earth’s crust. When magma reaches the surface, especially under an ocean, where it can be much closer to the crust, it slowly pushes the cooled rock up, creating volcanic mountains, a potential source for lava extrusion.
Earth is not the only planet on which magma exists. Recent research on Mars, compared to volcanoes in Hawaii, suggests a flow of molten rock beneath the crust. Studies in 2007 postulate that volcanoes on Mars, once thought to be extinct, may just be dormant.