Volcanoes

1. Volcanoes
Formation, Causes, Types, Geysers etc.
(ENGINEERING GEOLOGY)
LECTURE – 10
Instructor: Engr. Naeem Bashir AwanHITEC, University

2. Outline
1. Volcanoes
2. Formation of Volcanoes
3. Causes of Volcanoes
4. Nature & type of Volcanic Eruptions
5. Products of eruptions
6. Types of Volcanoes
7. Geysers

3. Volcano
Volcano is a landform on earth’s surface, where molten rocks,
gases and pyroclastic debris erupt through the volcanic vent.

4. Volcano
Different parts (Typical Volcano)
 Magma Chamber
 Main Vent
 Secondary Vent
 Crater
 Volcanic bombs
 Lava flow
 Ash Clouds

5. Volcano
A volcanic vent is an
opening exposed on
earth’s surface, from
where the volcanic
material is emitted. All
volcanoes contain a
central vent underlying the
summit crater of the
volcano.

6. Volcanoes
Definitions:
1) Magma - Molten rock beneath Earth's surface.
2) Vent - An opening in Earth's surface through which volcanic materials escape.
3) Flank - The side of a volcano.
4) Lava - Molten rock that erupts from a volcano that solidifies as it cools.
5) Crater - Mouth of a volcano, surrounds a volcanic vent.
6) Ash - Fragments of lava or rock smaller than 2 mm in size that are blasted into the air by
volcanic explosions.
7) Ash Cloud - A cloud of ash formed by volcanic explosions.
8) Sill - A flat piece of rock formed when magma hardens in a crack in a volcano.
9) Parasitic Cone - A small cone-shaped volcano formed by an accumulation of volcanic
debris.
10) Summit - Highest point; apex

7. Types of Volcanoes
Types of Volcanoes:
1. Active
2. Dormant
3. Extinct
Active - Eruptions can be anytime and often.
Dormant - Has been a while since it has erupted, but could at anytime.
Extinct - Meaning it hasn't erupted in a very long, long time so it probably
won't ever again.

8. Volcanic State Description Example
Extinct Volcanoes Extinct volcanoes will never erupt
again.
Ben Nevis, the tallest mountain in
Scotland, and the British Isles.
Dormant Volcanoes Dormant volcanoes have been in
the state of sleep or dormancy for
a very long period of time—
usually at least 2,000 years.
However, dormant volcanoes are
not extinct and, hence, could
erupt at any time.
Sakurajima, Japan.
Active Volcanoes Active volcanoes are considered
as immediate threats. Lava and
gases may erupt from these
volcanos, and/or these volcanoes
may show seismic activities. An
active volcano may have erupted
recently and is at a risk of erupting
again.
Mauna Loa, Hawaii

9. Types of Volcanoes
Types w.r.t shapes of Volcanoes:
The type of magma in the earth creates four different types volcanoes:
1. Cinder Cones
2. Shield Volcanoes
3. Composite Volcanoes
4. Lava Domes

10. Types of Volcanoes
Cinder Cones:
Cinder cones are circular or oval cones built from erupting lava that breaks into small
pieces as it shoots into the air. As small pieces fall back to the ground, they cool and
form cinders around the vent.
One of the most common types of volcanoes is the cinder cone.
Less dangerous compared to other types, cinder cones only grow to about 1,000-
1,200 feet tall.
Unlike some of the other types of volcanoes, cinder cones are usually created from a
single opening.

11. Types of Volcanoes
The opening of a cinder cone is a cone-shaped structure, while the steeps are
formed of the erupted, fragmented cinders that fall close to the chimney/vent.
The manner of eruption for cinder cones is relatively simple. When the lava erupts,
cinders of it are blown into the air. These fragmented cinders fall a short distance
from the opening, thus creating the cone.

13. Types of Volcanoes
Shield Volcano - Flat:
Another type of volcano is the shield volcano. Unlike cinder cones, shield volcanoes
can be very, very big in size. However, they are not as dangerous as that size might
make it seem. This is because the eruption of lava out of shield volcanoes is not
accompanied by pyroclastic material (bursts of gas and particles).
Shield volcanoes may be tall but tend to be very broad, with less steep slopes than
other volcanoes.
Shield volcanoes can be huge because of their ample supply of magma. For
example, Mauna Loa is a shield volcano that rises more than 30,000 feet above its
base on the bottom of the ocean.

14. Types of Volcanoes
If the magma is runny, the gas can escape easily and there will not be an
explosion. The magma just comes out of the mountain and flows down the
sides.
Shield volcanoes are shaped like a bowl or shield in the middle with long
gentle slopes made by the lava flows.
Examples include the volcanoes in Hawaii and Mount Etna.

16. Types of Volcanoes
Composite Volcano - tall and thin
If the magma is thick and sticky (like honey), the gas cannot escape, so it
builds up and up until it explodes sending out huge clouds of burning rock
and gas.
Composite volcanoes are steep-sided volcanoes composed of many layers
of volcanic rocks, usually made from thick sticky lava, ash and rock debris
(broken pieces).
Composite volcanoes are also known as strato-volcanoes.

17. Types of Volcanoes
Composite volcanoes are reasonably big and can rise up 8,000-10,000 feet.
Moreover, they can range anywhere from 1-10 km in diameter.
Their eruptions are dangerous and explosive in nature, with many layers of
lava and pyroclastic materials, the current of rock and gas that can reach
1,800°F and 450 mph, killing any living organism in its path immediately.
The general structure of composite volcanoes is tall and symmetrical and
with steep sides. Commonly, composite volcanoes erupt hot gases, ash,
lava, and pumice as well as stiff, slow-moving lava.

18. Types of Volcanoes
Composite volcanoes are believed to kill the most people because of their
deadly nature and high numbers.
Apart from their dangerous side, composite volcanoes are also famous
because they comprise some of the most beautiful mountains on planet
Earth. For example, Mount Fuji of Japan and Mount Shasta in California are
two famous composite volcanoes.
Examples include Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta and Lassen
in California, Mount Hood in Oregon, Mount St. Helens and Mount Rainier in Washington and
Mt. Etna in Italy

20. Types of Volcanoes
Lava Domes
Lava domes are formed when erupting lava is too thick to flow and makes a steep-
sided mound as the lava piles up near the volcanic vent.
Unlike composite and shield volcanoes, lava domes are of significantly smaller
stature. They are formed when the lava is too viscous to flow to a great distance.
As the lava dome slowly grows, the outer surface cools and hardens as the lava
continues to pile within.
Eventually, the internal pressure can shatter the outer surface, causing loose
fragments to spill down its sides. Generally, such lava domes are found on the flanks
of larger composite volcanoes.

22. Volcano Shape / Type Description
Cinder Cones Cinder cones are circular or oval cones made up of small fragments of
lava from a single vent that have been blown into the air, cooled and
fallen around the vent.
Composite Volcanoes Composite volcanoes are steep-sided volcanoes composed of many
layers of volcanic rocks, usually made from high-viscosity lava, ash and
rock debris. Mt. Rainier and Mount St. Helens are examples of this type
of volcano.
Shield Volcanoes Shield volcanoes are volcanoes shaped like a bowl or shield in the
middle with long gentle slopes made by basaltic lava flows. Basalt lava
flows from these volcanoes are called flood basalts. The volcanoes that
formed the basalt of the Columbia Plateau were shield volcanoes.
Lava Volcanoes Lava domes are formed when erupting lava is too thick to flow and
makes a steep-sided mound as the lava piles up near the volcanic vent.
The eruption of Mount St. Helens in 1980 was caused in part by a lava
dome shifting to allow explosive gas and steam to escape from inside

23. Causes of Volcanoes
What causes volcanoes to erupt?
The Earth's crust is made up of huge slabs called plates, which fit together
like a jigsaw puzzle. These plates sometimes move.
Between the Earth's crust and the mantle is a substance called magma
which is made of rock and gases.
When two plates collide, one section slides on top of the other, the one
beneath is pushed down. Magma is squeezed up between two plates.

24. Nature of Volcanoes
Nature of Volcanoes
Volcanoes are mountains but they are very different from other mountains; they are
not formed by folding and crumpling or by uplift and erosion.
Instead, volcanoes are built by the accumulation of their own eruptive products -- lava,
bombs (crusted over ash flows, and tephra (airborne ash and dust).
A volcano is most commonly a conical hill or mountain built around a vent that
connects with reservoirs of molten rock below the surface of the Earth.
The term volcano also refers to the opening or vent through which the molten rock and
associated gases are expelled.

25. Nature of Volcanoes
Nature of Volcanoes
Driven by buoyancy and gas pressure the molten rock, which is lighter than the
surrounding solid rock forces its way upward and may ultimately break though zones
of weaknesses in the Earth's crust.
If so, an eruption begins, and the molten rock may pour from the vent as non-
explosive lava flows, or if may shoot violently into the air as dense clouds of lava
fragments. Larger fragments fall back around the vent, and accumulations of fallback
fragments may move downslope as ash flows under the force of gravity. Some of the
finer ejected materials may be carried by the wind only to fall to the ground many
miles away. The finest ash particles may be injected miles into the atmosphere and
carried many times around the world by stratospheric winds before settling out.

26. Geysers
Geysers- are springs that throw boiling water high in the air. They are caused by
volcanic heat warming trapped ground water.

27.  HITEC University, Taxila
The End
“Everything has beauty, but not everyone can see.” – Confucius
“Happiness is not something ready made. It comes from your own actions.”– Dalai Lama