Transcript Cinder cones

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
• 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.
Calderas
 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
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.
Shield Volcanoes
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
Pyroclastic Density Currents (pyroclastic
LAVA
FLOW
flows and surges)
Structural Collapse: Debris flowAvalanches
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
LACCOLITH: Utah
BATHOLITH
BC Batholith
BATHOLITH: Half Dome
Yosemite Nat’n Pk Cal.