BY:
ROMIT
SHASHANK CHAUHAN
KAVIRAJ
What is a volcano?
A volcano is a place on the
Earth’s surface where hot,
molten rock (called magma)
breaks through.
It is a vent or 'chimney' that connects molten rock (magma) from within the Earth’s crust to the Earth's surface.
The volcano includes the surrounding cone of erupted material.
vent
cone
magma chamber
conduit
How and why do volcanoes erupt?
Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface.
◦ Same principle as hot air rising, e.g. how a hot air balloon works
◦ At depths > 20 km the temperature = 800-1,600 degrees Celsius
When magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it as to how it erupts.
Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption!
◦ Think about shaking a carbonated drink and then releasing the cap.
Small amounts of gas and (or) low viscosity (runny) magma will form an effusive eruption
◦ Where the magma just trickles out of the volcano (lava flow).
How do volcanoes work? Heat and pressure cause rocks to melt and form magma.
Magma needs to get out, too much pressure!!!!!!
Rise in temperature or drop in pressure causes magma to form faster.
How do volcanoes work? (cont.)
Magma is forced onto
Earth’s surface.
It dries and hardens,
this happens many
times over thousands of
years.
Eventually a mountain
called a volcano is
formed.
Areas of volcanism
Sub-ducting Boundaries Plate Sub-ducts below surface into mantle
Oceanic-Oceanic Volcanoes form near boundary
Mid Ocean Ridges Eruptions occur where plates are diverging
Hot spots
Where do most volcanoes occur?(cont.)
Volcanoes occur at
both divergent and
convergent boundaries
and also at hot spots.
Oceanic-Oceanic/Suducting
Graphic taken from:
http://147.205.15.81/geology/work/VFT-so -far/orogeny/pl.tect.html
Mid Ocean Ridges
Hot Spots
Graphic taken from:
http://volcano.und.nodak.edu/vwdocs/vw/lessons/atg.htm
l
Parts of a Volcano Most volcanoes share a specific
set of features.
The magma that feeds the eruptions pools deep underground in a structure called a magma chamber.
At Earth’s surface, lava is released through openings called vents.
Flowing lava in the interior travels through long, pipelikestructures known as lava tubes.
Magma: Molten rock beneath the surface of the earth.
Magma chamber: The subterranean cavity containing the gas-rich liquid magma which feeds a volcano.
Conduit: A passage followed by magma in a volcano.
Vent: The opening at the earth's surface through which volcanic materials issue forth.
Cone: A volcanic cone built entirely of loose fragmented material (pyroclastics) and (or) lava flows erupted from the vent. Erupted material builds up with each eruption forming the cone.
Types of volcanos:
On the basis of Activity:
i)Active ; ii) Dormant; ii) Extinct
a volcano is classed as “active” if it erupts lava, rock, gas or ash, or if it shows seismic (earthquake) activity.
A volcano is dormant if it hasn't erupted for a long time (less than 1 million years) but could again one day.
An extinct volcano will never erupt again.
Types of Volcanoes:
On the basis of type of erruption:
i)Explosive erruption
ii)Effussive erruption
Explosive Eruptions
Mt. Redoubt
Explosive volcanic eruptions can be catastrophic
Erupt 10’s-1000’s km3 of magma
Send ash clouds >25 km into the stratosphere
Have severe environmental and climatic effects
Hazardous!!! Above: Large eruption column and
ash cloud from an explosive eruption
at Mt Redoubt, Alaska
Direct
measurements of
pyroclastic flows are
extremely
dangerous!!!
Effusive Eruptions
Effusive eruptions are
characterised by outpourings
of lava on to the ground.
Hawaii
Courtesy of www.swisseduc.ch
On the basis of External structure:
Shield volcano: usually form at hot spots,
from non explosive eruptions
Cinder cone volcano: form from explosive
eruptions, very steep.
Composite volcano: form from both
explosive and non explosive eruptions.
Shield volcano
Form from many layers of “runny” lava.
Very wide, not to steep.
Biggest type of volcanoes
Tallest mountain in the world is Mauna Kea (measures from sea floor to top)
non explosive eruptions
Mauna Kea, Hawaii
Cinder cone volcano Smallest type of volcano
Most common
Made from pyroclastic material (material shot
out of a volcano)
Form a large crater
Explosive!
Paricutin, Mexico
Composite volcano:
Eruptions alternate between explosive
and non-explosive.
Sometimes they have runny lava layers,
other times the have pyroclastic materials
form layers.
Have a wide base and steep sides.
Have a crater
Mount Fuji
Mount Fuji
Some other types of volcanos
Stages of eruption:
Pyroclastic Flow
For example,
eruption of
Vesuvius in 79
AD destroyed
the city of
Pompeii
Pyroclastic materials
Material that is thrown into the air during
an explosion.
Volcanic bombs: large blobs of magma that
harden in the air.
Lapilli: pebble size rocks
Volcanic ash: tiny powder like material
Effects of volcanic eruption
Negative effects(destruction of lifeforms)
Positive effects
Pyroclastic flow
Mud flows
Pyroclastic fall
Lava flow
Noxious Gas
Earthquakes
Volcanic Hazards
Courtesy of www.swisseduc.ch
Pyroclastic Flow - direct impact
Courtesy of www.swisseduc.ch
Pyroclastic Flow - burial
Pyroclastic Flow - burns
Pyroclastic Flow – mudflow
Hot volcanic activity can melt snow and ice
Melt water picks up rock and debris
Forms fast flowing, high energy torrents
Destroys all in its path
Pyroclastic Fall
• Ash load
– Collapses roofs
– Brings down power lines
– Kills plants
– Contaminates water
supplies
– Respiratory hazard for
humans and animals
Lava Flow
It is not just explosive volcanic activity that
can be hazardous. Effusive (lava) activity is also
dangerous.
Positive effects
provide nutrients to the surrounding soil.
Volcanic ash often contains minerals that
are beneficial to plants
volcanic gases are the source of all the
water (and most of the atmosphere) that
we have today
Pompeii (79AD)
On August 24, 79AD Mount Vesuvius literally
blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the
atmosphere. Pyroclastic flows flowed over the
city of Pompeii and surrounding areas.
Pompeii (79AD)
Pyroclastic flows of poisonous gas and hot
volcanic debris engulfed the cities of Pompeii,
Herculaneum and Stabiae suffocating the
inhabitants and burying the buildings.
Pompeii (79AD)
The cities remained buried
and undiscovered for almost
1700 years until excavation
began in 1748. These excavations continue today
and provide insight into life during the Roman Empire.
Vesuvius today
Vesuvius remains a hazardous volcano with heavily populated flanks:
◦ around 1.5 million people live in the city of Naples alone
◦ Naples is situated approx. 30 km from Vesuvius
◦ Pyroclastic flows can flow up to 100 km from source!
Bay of
Naples
Vesuvius
Naples
Courtesy of www.swisseduc.ch
Volcanic explosivity index
The volcanic explosivity index (VEI)
was devised by Chris Newhall of the US
Geological Survey and Stephen Self at
the University of Hawaii in 1982 to
provide a relative measure of the
explosiveness of volcanic eruptions.
Volume of products, eruption cloud
height, and qualitative observations are
used to determine the explosivity value.
SUPERVOLCANO
A supervolcano is any volcano capable of producing a volcanic eruption with an ejecta volume greater than 1,000 km3 (240 cu mi).
This is thousands of times larger than normal volcanic eruptions.
Supervolcanoes can occur when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust, and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure (this is the case for theYellowstone Caldera
YELLOWSTONE RIVER IN HAYDEN VALLEY
1883 eruption of Krakatoa
The 1883 eruption of Krakatoa in
the Dutch East Indies (now Indonesia) began
on August 26, 1883 (with origins as early as
May of that year) and culminated with several
destructive eruptions of the remaining caldera
It was one of the deadliest and most
destructive volcanic events in recorded history,
with at least 36,417 deaths being attributed to
the eruption itself and the tsunamis it created
1883 eruption of Krakatoa(cont.)
average Northern Hemisphere summer temperatures fell by as much as 1.2 °C
The eruption darkened the sky worldwide for years
Ships as far away as South Africa rocked as tsunamis hit them, and the bodies of victims were found floating in the ocean for months after the event.
The explosion is considered to be the loudest sound ever heard in modern history, with reports of it being heard up to 4,800 km from its point of origin.
Famous volcanos around the world
Mt. Etna(active)
Mt Kilimanjaro (dormant)
Did you know?
Pumice stone, which comes from volcanoes, is very light because it contains lot of tiny bubbles. If there are enough bubbles, then pumice stone can float on water!
Mount Kilauea, in Hawaii, is the most active volcano on Earth because it has been erupting since 1983!
The word, ‘volcano’ comes from the name Vulcan, who was the Roman god of fire.