section 9.3 volcanic landforms. notes 9.3 types of volcanoes make this chart in your notebook page...
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Section 9.3
Volcanic Landforms
Notes 9.3 Types of Volcanoesmake this chart in your notebook page 203
Size, shape
Draw a diagram
Slope:
Boundary:
TIME to form
LAVA type:
ERUPTION:
Examples:
shield cinder Compositestratovolcano
Shield
• Broad, slight dome shape• gently sloping • TIME: Slow to form• Divergent, mid-ocean ridge, hot spots • LAVA: Very fluid – mafic basaltic lava, low gas,
low silica (< 50%), low viscosity, high temps. pahoehoe- very little pyroclastic material
• Quiet eruptions V.E.I. 0 – 2• Hawaiian Islands are composed of 5 shield
volcanoes -Mauna Loa is the largest in Hawaii-Kilauea is the most active, having erupted more than 50 times
Cinder cone
• Frequently appear in groups around larger volcanoes at any boundary.
• Rather small in size (less than 1000 feet)• Steep slopes (30-40 degrees) form when molten lava is
thrown up into the air from a vent and hardens into fragments before coming straight down to the ground
• Forms fast! From months to a few years• Lava is ejected fragments: ash, cinders, lapilli, pumice,
scoria - - the Paricutin (Mexico City) formed from a cornfield rather quickly (2 years)-
Composite Cones
• Large, nearly symmetrical mountain structures composed of alternating layers of lava and pyroclastics
• Thick, viscous, slow-moving lava, • Felsic / andesitic lava, high silica (70% - more) • Pyroclastic flows: ash, fragments, and steam clouds that
race down steep slopes at speeds of 125 mph• Most explosive and violent type of volcano• Around “Ring of Fire”, convergent/subduction, O-O, O-C• Mt. Visuvius,Cascade Range in NW U.S. Mt. St. Helen
Pyroclastic Flows
Lahar
Mt. St. Helen
COMPOSITE VOLCANOShape: Broad/flat Steep symmetrical
Size: Largest area Highest smallest
Boundary: Convergent Divergent hotspot
Magma: Mafic (basalt) Felsic (rhyolite)
Eruption: Violent/gassy quiet
Other: Pyroclastic flows Pahoehoe lava Cinders/ash
SHIELD VOLCANO(Circle one answer for each category)
Shape Size Plate boundary
Broad/flat Largest area Convergent
Steep Highest Divergent
Symmetrical smallest hotspot
Magma Eruption Other
Mafic (basalt) Violent/gassy Pyroclastic flows
Felsic (rhyolite) quiet Pahoehoe lava
Cinders/ash
CINDER CONEShape: Size: Boundary:
Broad/flat Largest area Convergent
Steep Highest divergent
Symmetrical smallest hotspot
Magma: Eruption: other:
(basalt)mafic Violent/gassy Pyroclastic flow
(rhyolite) felsic quiet Pahoehoe lava Cinders/ash
Answers: COMPOSITE volcanoShape: Broad/flat Steep symmetrical
Size: Largest area Highest smallest
Boundary: Convergent Divergent hotspot
Magma: Mafic (basalt) Felsic (rhyolite)
Eruption: Violent/gassy quiet
Other: Pyroclastic flows Pahoehoe lava Cinders/ash
Answers: SHIELD VOLCANO(Circle one answer for each category)
Shape Size Plate boundary
Broad/flat Largest area Convergent
Steep Highest Divergent
Symmetrical smallest hotspot
Magma Eruption Other
Mafic (basalt) Violent/gassy Pyroclastic flows
Felsic (rhyolite) quiet Pahoehoe lava
Cinders/ash
Answers:CINDER CONEShape: Size: Boundary:
Broad/flat Largest area Convergent
Steep Highest divergent
Symmetrical smallest hotspot
Magma: Eruption: other:
(basalt)mafic Violent/gassy Pyroclastic flow
(rhyolite) felsic quiet Pahoehoe lava Cinders/ash
Calderasand
Lava Plateaus
Collapsed cone
• A caldera is a bowl-shaped depression or basin at the summit of a volcano
• which forms when the summit collapses
• after the magma chamber has been mostly emptied after it erupted
Mazama started to grow around 400,000 years ago.
Over time much of the c.4000 foot (c.1200 m) depth of the caldera was filled with volcanic material. The rest was filled with water from snowmelt and rain to eventually form Crater Lake.
Crater Lake in Oregon
At 1,943 feet deep, Crater Lake is the deepest lake in the United States and the seventh deepest lake in the world!
Features beneath the surface of Crater Lake constructed using data from the 2000 bathymetry survey.
Colors range from orange to blue with increasing water depth.
Yellowstone National
Park is/was a
caldera
The caldera has been partially filled or “flooded” with lava.
Lava plateaus
Flood BasaltsWhen huge volumes of basalt lava erupt rapidly, their flows spread out and no 'volcano' is formed at all - just a huge flat plain of lava flow.
Such huge effusions of lava are moderately common in Earth's past.
The Columbia River Basalts cover 500,000 square kilometers, and are up to 2000 meters thick, for a total volume of near 170,000 cubic kilometers.
Layers of igneous rock show evidence of repeated lava flows.
A thick layer of basaltic lava that once flooded over the land
Obsidian Mountain , WY.
World flood basalts
Slow, cooled columns of basaltic lava several meters high.
Northern Ireland