Mountain building & volcanism md. yousuf gazi

VOLCANISM
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

Geological Processes
I. Endogenetic Processes: Those operate within the Earth's crust,
viz. earthquake, volcanic eruption.
II. Exogentic Processes: Those which are active on the Earth’s
surface, viz. weathering, erosion.
Geological processes: A number of processes which shape the planet on which we live
and concentrate the resources on which we depend.

Endogenetic Geological Processes
1. Mountain Building
2. Volcanism 3. Plate Tectonic 4. Earthquake.

Global Topography

Global Distribution of Active Volcanoes

Volcanism
• The process whereby magma and associated gas rises through the crust
and are extruded onto the surface or into the atmosphere.

Volcanoes
• Conical mountains formed around a vent where lava, gas, and pyroclastics are erupted to the surface.
• Main crater (circular depression) at the summit fed by a volcanic pipe. Subordinate vents on the
volcano flanks may also extrude material (parasitic cones).
• Calderas: Characterize large volcanic craters like those responsible for ignimbrites and
“supervolcano” eruptions. Exceed 1 km in diameter with steep sides.
Calderas

Shield Volcano: Resemble an upside-down shield with low, rounded
profiles and gentle slopes (2-10 degrees max). Basaltic lava flow.
Types of Volcanoes

Cinder Cone: Volcanic peak composed of pyroclastic materials resembling cinders
(scoria, pumice, lapilli, and ash).

Composite Volcano: (Stratovolcanoes) Built of both lava flows and pyroclastics in
layers. Usually andesitic composition material. Large, high mountains with concave
profiles (steep summit and shallow flanks).

Lava Dome: Characteristic of viscous (e.g. cool & felsic) magmas. Bulbous, steep-
sided constructs, often in the craters of larger composite volcanoes.

Volcano Types
9 km
3 km
0.3 km
Shield volcano (e.g. Mauna Loa, Hawaii)
Composite or Stratovolcano (e.g. Mt. St. Helens, Washington)
Cinder cone (e.g. Sunset Crater, Arizona)
150 km
15 km
1.5 km

Products of Volcanism
• Volcanic Gas
• Lava flows
– Pahoehoe
– Aa
– Lava lakes & fountains
– Lava channels & tubes
– Columnar joints
– Pillows
• Pyroclastics
– Ash
– Lapilli
– Volcanic bombs & blocks
– Lahars, mudflows, etc.
– Nuee ardente
– Tuff
• Constructional features (volcanoes)

Volcanic Gas

Lava flows

Pyroclastics

Styles of Volcanic Eruption
• Hawaiian
• Strombolian
• Vulcanian
• Pelean
• Plinian
• Surtseyan (Phreatic)
• Other
– Mid-ocean ridge
– Supervolcanoes
– Continental Flood
Basalts

• Mountains are landforms that rise at least 1,000 feet above the surrounding landscape. They must
be a minimum of 1000 feet from summit to base. They fall into one of four different categories that
depend on the way they were formed:
1. Volcanic Mountains: produced by rising plumes of mantle material either near rift zones, plate
boundaries or in the centres of plates over hot spots.
Mountain Building

Continental rift zones: as in the Great Rift Valley of eastern Africa where splits in the plate are filled
by rising mantle material. Material rises as a result of deep mantle convection.
1. Volcanic Mountains:

 Mid Oceanic ridges: rift zones such as the Mid-Atlantic rift where oceanic plate material is
produced. Same as continental rift zones but under water.

 Hot Spots: such as Hawaii, are shield cone volcanoes produced where rising mantle hot spot
material breaks through plate material in isolated areas as the oceanic plate drifts across the hot
spot. Hot spots on continental plates do not result in the formation of volcanoes but in hot springs
and geysers.

 Subduction zone: volcanoes such as Mount St. Helens and Fujiyama are produced where subducted
material is returned to the surface inland of the subduction zone itself.

Mountain Building
2. Orogenesis is the formation of mountains. This process tends to be concentrated in specific
areas depending on the type of mountain being formed.

• Ocean-Continent Orogenesis: process resulting from the convergence of an oceanic plate and a
continental plate. The subduction of the oceanic plate leads to the formation of some volcanic
mountains as well as folded mountains. Examples: Andes Mountains, Sierra Nevada
West Coast of South America
Andes Mountains

• Ocean-Ocean Orogenesis: process resulting from the convergence of two oceanic plates. The
subduction of one of the two plates leads to the formation of an arc of islands that are primarily
volcanic in origin, with only the tallest peaks visible above the water's surface. Examples:
Japanese islands, Aleutian islands, Puerto Rico, Bahamas.

• Continent-Continent Orogenesis: process resulting from the convergence of two continental plates.
Neither plate is truly subducted. No volcanic activity results. Seriously high and folded mountains
result. Example: Himalayas
SE
Asia
Himal
aya
Tibeta
n
Platea
u
60 million years ago
30 million years ago
Today
Indian
Plate
(continental)
Eurasian
Plate
(continental)

Convergent Boundaries
ocean-continent
“subduction zone”
(Andes Mtns)
ocean-ocean
“subduction zone”
(Japan, Aleutians)
continent-continent
collision zone
(Himalayas, Alps)

2. Domal and Block-Fault Mountains: produced by forces that result in the upwarping of the earth’s
surface.
– Local doming: Rising subsurface materials result in the upward warping or pushing of material
with sizes between 50 and 100 miles. Upwarping typically results in the erosion of materials as
the doming is underway.
– Regional doming: Uplift of larger areas, such as the Colorado Plateau, that results in the
formation of entire mountain ranges with these same characteristics.
3. Block-Fault: Formation of mountains as faulting causes the boundary lines necessary for the uplift
and possible rotation of chunks of surface materials. May produce horsts and grabens when blocks of
material are uplifted or sink into the ground respectively.
4. Foldbelt Mountains: Generated at the boundaries of convergent plates when layers of materials are
squeezed and buckle due to the pressure. Results in the formation of anticlines and synclines.
Mountain Building

Thank you…..

Mountain building & volcanism md. yousuf gazi

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