incr easing heat & pr essur e crust mantle magma • liquid rock • gases • water granite basalt pumice obsidian crust magma lava Magma Magma is a mixture of liquid rock, gases and water formed from intense heat and pressure in the Earth’s mantle. Not all magma is the same. The composition and viscosity of magma can vary. These properties affect how fast the lava flows and the type of volcano that forms. Viscosity is a liquid's resistance to flow. High viscosity magma is sticky and flows very slowly. Low viscosity magma flows more quickly. Higher temperatures make magma and lava more fluid, lowering the viscosity. Pahoehoe is a type of very hot, fast-moving lava with low viscosity. Slower-moving, cooler, high-viscosity lava is known as aa. Different Types of Lava Magma with high silica content has a higher viscosity and produces light-colored lava that later forms rhyolite. Magma with less silica and a lower viscosity produces dark lava that forms basalt. aa - high viscosity pahoehoe - low viscosity Magma, Lava & Igneous Ro ck Mt. Saint Helen’s © Copyright NewPath Learning. All Rights Reserved. 94-4672 Visit www.newpathlearning.com for Online Learning Resources. Photos courtesy of USGS. What Is a Volcano? A volcano forms when magma moves through the crust and erupts onto the surface of the Earth. Magma that flows onto the Earth's surface is called lava. Layers of cooled lava harden into igneous rock and build up on the Earth's surface around a volcano. Igneous rock also forms when magma cools and hardens under the Earth’s crust.
incr easing heat & pr essur e • liquid rock • gases • water Pause and Review Label the images below. © Copyright NewPath Learning. All Rights Reserved. 94-4672 Visit www.newpathlearning.com for Online Learning Resources. Magma, Lava & Igneous Ro ck