Chapter 9 Volcanoes Vocabulary: Aa: A solidified basaltic lava flow on land that has formed with rough, jagged surfaces. Caldera: base level. The level of the body of water into Cinder Cone: A cone-shaped volcano formed from lava fragments that have been ejected from a volcanic vent. Composite Volcano: A volcano made of layers of hardened lava flows and pryoclastic materials Hot Spot: An area of volcanic activity that results from a plume of hot solid material that has risen from deep within Earth’s mantle. Lahar: a fast-moving mudflow that occurs when the heat associated with a volcanic eruption melts snow and ice on top of a volcano. Lava: Magma that reaches Earth’s surface. Lava Plateau: A plateau formed from basaltic lava pouring from a crack or fissure in Earth’s surface. Pahoehoe: Solidified basaltic lava flow on land that has formed with smooth, ropelike surfaces. Pillow Lava: Lava that cools underwater, taking on a distinctive pillow-like shape as it hardens. Pyroclastic Flow: A dense, superheated cloud of gases and pyroclastic material that moves rapidly downhill from an erupting volcano. Pyroclastic material: Solid rock fragments that are ejected during a volcanic eruption. Shield Volcano: A shield-shaped volcano with a broad base and gently sloping sides that is made of basaltic lava. Viscosity: A substance’s resistance to flow. Volcano: An opening in Earth’s crust through that molten rock, gases, and ash erupt; also, the landform that develops around this opening.