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.