Volcanic Structures.docx

8/12/2019 Volcanic Structures.docx

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Volcanic Structures

Figure 1 Types of Volcanoes

CINDER CONES- are produced by the eruption of viscous magma and are composed almost

entirely of pyroclastic deposits. These angular fragments form steep (30-40o)

and usually small

(< 1000') cones.


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Figure 3 Mayon volcano

MAAR - Also called "tuff cones," maarsare shallow, flat-floored craters that scientists interpret

have formed above diatremes as a result of a violent expansion of magmatic gas or steam; deep

erosion of a maar presumably would expose a diatreme.


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Figure 4Zuni Salt Lake Maar, New Mexico

VOLCANIC PLUGS- believed to overlie a body of magma which could be either still largely liquidor completely solid depending on the state of activity of the volcano. Plugs are known, or

postulated, to be commonly funnel shaped and to taper downward into bodies increasingly

elliptical in plan or elongated to dike-like forms.

Figure 5 Ship rock, New Mexico

LAVA DOMES- are formed by relatively small, bulbous masses of lava too viscous to flow any

great distance; consequently, on extrusion, the lava piles over and around its vent. A dome

grows largely by expansion from within. As it grows its outer surface cools and hardens, then

shatters, spilling loose fragments down its sides.


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Figure 6 Novarupta dome, Alaska

SHIELD VOLCANOES- are built almost entirely of fluid lava flows. Flow after flow pours out in

all directions from a central summit vent, or group of vents, building a broad, gently sloping

cone of flat, domical shape, with a profile much like that of a warrior's shield.

Figure 7 Mauna Loa, Hawaii

GEYSERS, FUMAROLES (SULFATARAS), HOT SPRINGS- springs are generally found in regions of

young volcanic activity. Surface water percolates downward through the rocks below the


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Earth's surface to high-temperature regions surrounding a magma reservoir, either active or

recently solidified but still hot.

Figure 8 Old Faithful Geyser, Wyoming

FISSURE VOLCANO -This type of volcano has no central crater at all, which makes it difficult to

recognize either from the ground or from space. Instead, giant cracks open in the ground and

expel vast quantities of lava that spread far and wide to form huge pools that can cover almost

everything around.

Figure 9 The 2010 fissure eruption at Eyjafjallajokull

FLOOD BASALT PROVINCES- This is another strange type of "volcano". Some parts of the world

are covered by thousands of square kilometers of thick basalt lava flows--some flows are more

than 50 meters thick, and individual flows extend for hundreds of kilometers.


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LAVA MOUNDS- Some basaltic volcanoes have no sign of a crater, but are gently sloping

mounds

Figure 12 Mount Cottrell, Victoria

CUMULO-DOMES- When viscous lava is extruded, it sags and spreads into convex dome-like

bodies called cumulo-domes. These may be almost independent, or may be associated with andpartly intrusive into previously deposited pyroclasts.

Figure 13 Lassen Peak

MONOGENETIC FIELDS- don't look like "volcanoes", rather they are collections of sometimes

hundreds to thousands of separate vents and flows. Monogenetic fields are the result of very

low supply rates of magma.


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Figure 14 San Fransisco volcanic field

SOURCES:

http://pubs.usgs.gov/gip/volc/types.html

http://www.geocities.ws/alhy731/volcanoes/type.html

http://geography.unt.edu/~williams/geog_3350/examreviews/volcanic_structures.htm

http://geoenviron.wordpress.com/2012/02/24/structure-of-volcanoes/
http://pubs.usgs.gov/gip/volc/types.htmlhttp://pubs.usgs.gov/gip/volc/types.htmlhttp://www.geocities.ws/alhy731/volcanoes/type.htmlhttp://www.geocities.ws/alhy731/volcanoes/type.htmlhttp://geography.unt.edu/~williams/geog_3350/examreviews/volcanic_structures.htmhttp://geography.unt.edu/~williams/geog_3350/examreviews/volcanic_structures.htmhttp://geography.unt.edu/~williams/geog_3350/examreviews/volcanic_structures.htmhttp://www.geocities.ws/alhy731/volcanoes/type.htmlhttp://pubs.usgs.gov/gip/volc/types.html

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