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Lava is the name for magma—molten rock—after it erupts from a volcano. Since volcanoes erupt in different ways, cooled lava takes on different forms.
Explosive Lava
When lava erupts explosively and cools before it hits the ground, it forms fragments. Different sized fragments have different names, from giant “volcanic bombs,” to little stones called lapilli, to minute particles of ash. Ash particles can also bond together like concrete to form a rock-hard layer called tuff.
Runny Lava
Hawaiian volcanoes erupt runny, flowing lava called pahoehoe (pah-HOY-hoy). Pahoehoe is runny because it is low in the chemical compound silica, which forms long molecular chains that make magma thick and goey. Runny lava holds in less gas, so it flows gently rather than exploding when it erupts.
Runny lava can take on many unusual forms, including that of volcanic glass, which can result when runny lava cools too quickly for crystals to form. Some of its forms look glassier than others:
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Pele’s hair (named after the Hawaiian goddess Pele) forms when lava that erupts like a fountain or cascades like a waterfall cools quickly into glassy strands.
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Obsidian is liquid rock that cools quickly into thick chunks of glass. Different minerals give obsidian different colors; magnetite makes it inky black, and hematite gives it mahogany-red streeks. Obsidian containing the mineral wüstite can have a greenish color.
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Pumice is the form lava takes when it erupts in a frothy mass of gas bubbles that cool quickly. |
Continue to The Krakatoa Explosion. >>
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