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.

Kilauea caldera

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