STRUCTURES DUE TO
VOLCANISM
INTRUSIVE AND
EXTRUSIVE VOLCANIC
LANDFORMS

VOLCANISM :
•
Defined as the transfer of magma from one area of the earth to another, due to a change in the pressure of the earth. It is the drop in pressure that allows the semi-liquid molten rock to become liquid and rise to the top.

EXTRUSIVE FORMS
•
When magma reaches the surface of the earth.
•
Extrusive forms have been exposed by erosion or released in the form of lava.
•
The volcanic shape (cone) is considered an extrusive feature.

PARTS OF A VOLCANO
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A cone or crater at the top.
•
When the cone walls break away, the basin which is left over is a caldera .
•
Sometimes, this is filled with water and is called a crater lake .

 range in shape from circular to oblong. These depressions are formed by collapse of the central vent during the extrusion of pyroclastic materials.

Their diameters are many times larger than those of associated vents.

CONE OR
CRATER:
Wizard Is. OR

CALDERA

Domes

Lava domes form by the slow extrusion of highly viscous silica-rich magma

Domes can be solitary volcanoes, form in clusters, grow in craters or along the flanks of composite cones.

A dome has been growing slowly within the crater of Mount St. Helens since the eruption of 1980. Domes have also filled the crater of Mt. Pelée, Martinique, etc.

TYPES OF VOLCANOES
•
The type of volcano is dependent upon what type of plate boundary it is at and what type of magma is extruded
•
There are 3 types: cinder, shield, and composite volcanoes.

CINDER CONE
•
Mainly acidic or SIALIC magma is extruded. The rock cools quickly in the form of cinder and ash. This results in steep sides and a narrow neck. This volcano can become plugged easily and thus is explosive in nature.


Cinder cones are mounds of basaltic fragments.

Streaming gases carry liquid lava bombs into the atmosphere that rain back to earth around the vent to form a cone.

CINDER CONE

CINDER CONE: Diamond Head

CINDER CONE: ARIZONA

Cinder Cone: Pu`u ka Pele – Maui

SHIELD CONE
•
Mainly basic or SIMATIC magma is extruded. The rock cools very slowly and forms low cones and wide sheets of lava. Free flows and slow cooling means low explosiveness.

large volcanoes with broad summit areas and low-sloping sides
- low viscosity basaltic lava flows.

SHIELD CONE

SHIELD CONE: Mauna Kea Hawaii

SHIELD CONE: Haleakala
10000 ft above, 18000 ft below

Gabi Laske – Iceland

COMPOSITE CONE
•
Formed by the mixture of SIALIC AND
SIMATIC magma. This builds up alternate layers of cinder ash and lava.
As a result, both great width and height are attained, making the world’s largest volcanoes.
•
Most common in oceanic-continental subduction zones, where there is a mixture of simatic and sialic rock

Composite Continued
•
Also known as – Strato Volcanoes
• built by multiple eruptions, sometimes recurring over hundreds of thousands of years, sometimes over a few hundred.

COMPOSITE CONE

COMPOSITE CONE: Mt Fuji

COMPOSITE CONE: Mt. Rainier

Mount Rainier

COMPOSITE
CONE:
Mt. St Helens

MT ST HELENS MAY 18, 1980

MT ST HELENS MAY 18, 1980

BEFORE:

AFTER:

VOLCANO CLASSIFICATION
•
Active means they show signs of movement and unrest
•
Dormant shows possibilities of future unrest
•
Extinct show no signs of any activity

DESTRUCTIVE EFFECTS:
•
Lava flow and explosive rock can destroy surrounding countrysides.
•
Cinder ash can bury surrounding areas and affect weather patterns worldwide
•
Tidal waves (tsunamis) can result
•
Nuee ardentes, clouds of super-heated steam and gas can blow down the mountain destroying all in its path.

List of Volcanic Hazards flows and surges)
Structural Collapse: Debris flow-
Avalanches
Dome Collapse and the formation of pyroclastic flows and surges
Lava flows
Tephra fall and ballistic projectiles
Volcanic gas
Tsunamis

CINDER ASH and MUDFLOW
(lahar)

CINDER ASH and MUDFLOW

NUEE ARDENTE (pyroclastic flow)
A cloud of hot gas and ash, etc from a volcano, spreading horizontally.

INTRUSIVE FORMS:
•
When magma goes into the lithosphere but does not reach the surface
•
The magma will fill cracks and force spaces open with the lithosphere
•
These formations are often sought after for their mineral concentrations.

INTRUSIVE FORMS:
•
DIKE: magma cools in a vertical crack forming a wall
•
SILL: magma cools in a space between sedimentary layers forming a thin sheet
•
LACCOLITH: feature created when magma fills a hollow or cavern. The form the surface takes when pushed up from underneath by magma (called a laccolithic dome)
•
BATHOLITH: Larger version of a laccolith.
When so much magma has intruded that the intrusion has no known depth. B.C.’s coast has a huge granite batholith.
•
Diagram: page 74

DIKE: Ship Rock N.M.

SILL: in Scotland

LACCOLITH: Utah

BATHOLITH

BC Batholith

BATHOLITH: Half Dome
Yosemite Nat’n Pk Cal.