Aardvark Communications' Volcano Guide

Can you define the following terms?

• aa: A Hawaiian term for a lava flow that has a rough, jagged surface.
• batholith: A large, discordant, intrusive body of igneous rock.
• barchan: A crescent-shaped sand dune with horns pointing downwind.
• caldera:A large, basin-shaped volcanic depression, more or less circular in form. Typically steep-sided, found at the summit of a shield volcano .
• chert: A cryptocrystalline form of quartz, microscopically granular. Occurs as nodules and as thin, continuous layers.
• coquina: A coarse-grained, porous variety of clastic limestone made up chiefly of shells and shell fragments.
• gas: produced by the volvano during eruption ion the form of steam, this gas includes carbon dioxide, nitrogen, and sulphur dioxide.
• lahar: A mudflow composed chiefly of pyroclastic material on the flanks of a volcano.
• lava: magma that has escaped to Earth's surface. Can be hotter than 2000 degrees F.
• pahoehoe: A Hawaiian term for a basaltic lava flow with a smooth, or ropy surface. compare aa.
• Tephra: fragments of lava blasted into the air. Sizes range from dust four feet across. Some weigh 100 tons.
• remanent magnetism:Magnetism acquired by a rock as some time in the past.