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58 terms

Earth Science Chapter 18

All of the questions are from the chapter 18 power point in class notes.
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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.