Earth Science Chapter 18
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58 terms
Terms | Definitions |
|---|---|
 Volcanism | All the processes associated with the discharge of magma, hot fluids, and gases. |
| Volcano | Both the opening in the Earth's crust through which molten rock, gases, and ash erupt and the landform that develops around this opening. |
| The Ring of Fire | The zone of volcanic activity surrounding the Pacific Ocean. |
| Convergent Volcanism | Volcanoes form on the overriding plate as subducting plate melts to form magma. |
| If convergent boundary is ocean/continent, then the chain of volcanoes is where? | On land |
| What forms when a convergent boundary is ocean/ocean? | A volcanic island arc |
| Example of a chain of volcanoes on an ocean/continent convergent boundary | Cascade Range of Pacific Northwest |
| Example of a volcanic island arc on an ocean/ocean convergent boundary | Mariana Islands |
| Where does most magma reach Earth's surface? | At divergent boundaries |
| When magma reaches the surface what does it do? | Fills in gap as plates move apart. |
| What type of magma does divergent volcanism contain? | Basaltic |
| Almost all divergent volcanism is (1)_________. Except in (2)__________. | (1) underwater. (2) iceland |
| Hotspots | Areas of volcanic activity that result from plumes of hot solid material that have risen from deep within Earth's mantle. As this rises, it melts to produce magma. |
| What do hotspots form and how? | Forms islands as plate moves over spot if in water. |
| Example of a hotspot | Hawaiian Islands |
| What happens when a hotspot is under land? | It erupts through cracks (called fissures) and forms flood basalts, resulting in lava plateaus. |
| Fissure | A crack in the ground |
| Example of a hot spot under land | Columbia River basalts; Deccan Traps, India. |
| Conduit | Tube-like structure lava travels through to reach the surface. |
| Vent | Opening on the surface at the end of the conduit. |
| Crater | Bowl-shaped depression around the vent at the top of a volcano. |
| Caldera | Forms when the top of a volcano collapses after an eruption empties part of the lava chamber underneath it. |
| What do types of eruptions and lava that form it determine? | Shape and structure |
| Shield Volcanoes | Made with basalt. Very fluid and will flow long distances before cooling. Volcanoes have a very broad, circular base with shallow slope. Largest type of volcano. Non-explosive eruptions. |
| What are shield volcanoes made with? | Basalt |
| Example of a shield volcano | Mauna Loa, Hawaii. |
| What type of lava are in cinder cone volcanoes? | Usually basaltic |
| Cinder Cone Volcano | Molten lava thrown into air from vent, form solid fragments that fall on ground around vent. Cone-shaped mound with oval base and steep sides. Smaller than other types, often found in groups. |
| Tephra | solid material ejected from a volcano during an eruption |
| Another name for a composite volcano is a ________. | Stratovolcano |
| Composite Volcano | Mixed layers of lava flows and more explosive pyroclastic material. |
| Example of a composite volcano | Mount Rainier, Washington. |
| 3 conditions which allow solid asthenosphere to melt and form magma | 1.) Decrease in pressure- divergent zones where lithosphere thinner and exert less pressure. 2.) Increase in temperature- hot spots. 3.) Increase in water in asthenosphere- subduction boundaries. |
| Viscosity | Resistance to flow. Determined by amount of silica and temperature. |
| The more silica magma contains then... | The slower the magma moves |
| Basaltic Magma | <50% Silica, low viscosity, non-explosive. Rifts and ocean hot spots. |
| Andesitic Magma | 50-60% Si, medium viscosity, medium explosivity. Subduction boundaries. |
| Rhyolitic Magma | >60% Si, high viscosity, high explosivity. Hot spots under continents. |
| Lava | Magma that reaches the Earth's surface. |
| Pahoehoe | ropelike in appearance. |
| What forms pahoehoe? | Hot, quick flowing lava on land |
| Aa | blocky in appearance. |
| What forms aa? | Cool, slow moving lava on land |
| What forms pillow lava? | Lava underwater |
| Pillow Lava | pillow-like appearance. |
| Pyroclastic Material | ejected lava when trapped gases escape. |
| What are ash and lava classified by? | Size |
| How big is ash? | < 2 mm |
| How big is lapilli? | 2 - 64 mm |
| How big are blocks and bombs? | > 64 mm |
| Pyroclastic flow | a dense, superheated cloud of gases and pyroclastic material that travels downhill at high speed. |
| Plutons | Intrusive, igneous rock bodies. |
| Batholith | Irregularly shaped mass of coarse-grained igneous rocks that cover at least 100 km2 and take millions of years to form. Common in interior of mountain chains. |
| Stock | Similar to batholiths but smaller in size. |
| Laccolith | A lens-shaped pluton with a round top and flat bottom. |
| Sill | When magma intrudes parallel to layers of rock. |
| Dike | A pluton that cuts across pre-existing rocks. |
| Volcanic neck | When the magma in a volcano conduit solidifies. |
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