Download volcano 1

Volcanoes
Magma
Simple put, a volcano occurs when magma
erupts onto the surface (land or under the ocean)
Magmas originate at depths between 50 and 250
kilometers (30 to 150 miles) beneath the crust
Source of Magma
Magmas can reach the surface
in one of three plate tectonic
settings:
Divergent plate boundaries
Subduction zones
“Hot spots”
Types of Volcanoes
Common types of
magma eruptions
Shield volcano
Cinder cones
Composite volcano
Caldera
Fissure
Flood basalt
Shield Volcano
Non-explosive eruptions of dark, fluid,
basaltic magma high in Fe and Mg.
Low viscosity of the magma allows for the
flow off the mountain making the shield
shape.
Example: Mauna Kea, Mauna Loa,
Hualalai, and Kilauea which make
up the “big island” of Hawaii.
Shield Volcanoes
•
•
•
•
•
Low silica level
Low viscosity Lava
High or low levels of gas
Flattened mound
Resembles a warrior’s shield
Composite or Stratovolcano
Explosive andesitic viscous magma rich in
silica that is layered with lava and rock
from old eruptions.
Periods of inactivity followed by huge,
violent explosions.
QuickTime™ and a
decompressor
are needed to see this picture.
Composite Volcanoes
•
•
•
•
•
•
High in silica
High viscosity magma
High levels of gas
Highly explosive
Cone shaped
Formed by layers of lava and ash
Cinder Cone Volcano
Non-explosive eruptions of
basaltic magma high in iron.
Produces tephra (ash, dust,
rocks, & lava bombs).
Steep sided with a conical
shape.
Very common type of volcano.
Example: Paricutin,
Mexico. This volcano
erupted in a field in
1943.
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
Cindercones
•
•
•
•
Low silica lava
High levels of gas
“Fire-fountain” eruptions
Commonly found on the flanks of shield
volcanoes
• Made from a pile of rock pieces
• Structurally weak
Mount St. Helens
Mount St. Helens in
Washington is a composite
volcano
On March 16, 1980 the first
of a series of minor
earthquakes occurred
under the volcano
This marked the beginning
of a new eruption cycle
It had been ~350 years
since the last eruption
ON YOUR PHYSICAL MAP, OUTLINE ALL OF THE
COUNTRIES THAT TOUCHES THE PACIFIC OCEAN. ALONG
YOUR OUTLINE, DRAW A VOLCANO SYMBOL.
Mid-Ocean Ridge/Underwater
Pillow lavas above,
Black smoker at midocean ridge, &
Iceland erupts
Divergent boundary produces usually fluid basaltic
magma. Large rifts may erupt volumes of lava.
Underwater pillow lavas may form.
Seamounts
There are more than a million seamounts in the oceans
(only a couple thousand are plotted on the map below)
So there are far more volcanoes under the sea than on
land
Hot Spot Volcanism
The Hawaiian Islands are the classic
example of hot spot volcanism
Hot Spot Volcanism
Every island in the Hawaiian Island chain was
created by volcanic eruptions that occurred as
the Pacific Oceanic Plate crossed over a hot spot
Hot Spot Volcanism
Hot Spot Volcanism
The plate has
moved to the
northwest for
more than 65
million years
The big island
of Hawaii is
now over the
hot spot
Main areas of hot spot activity
globally
TOPS Top 10 Geography in conjunction with www.sln.org.uk/geography
Continental Volcanic Hot Spots
Yellowstone Caldera Chain formed as the North
America Plate moved to the west southwest
The ages of the Yellowstone Calderas formed
over the hot spot range from 16 million years
ago to the present
Continental Volcanic Hot Spots
Currently, volcanic activity is exhibited only via
numerous geothermal vents, including Old
Faithful Geyser, but within the past two million
years, it has undergone three extremely large
explosive eruptions, up to 2,500 times the size
of the 1980 Mount St. Helens eruption
Continental Volcanic Hot Spots
The brown area marks the extent of the ash fall
Volcanic Hazards
How Bad Can It Be?
1815
1822
1826
1883
1902
1902
1919
1951
1982
1985
Indonesia
Indonesia
Indonesia
Indonesia
Martinique
Guatemala
Indonesia
New Guinea
Mexico
Columbia
92,000 killed
5,500 killed
3,000 killed
36,417 killed
29,025 killed
6,000 killed
5,110 killed
2,942 killed
1,700 killed
23,000 killed
How Bad Can It Be?
Causes of volcanicrelated deaths Over
the last 2,000 years
Pyroclastic Material
Pyroclastic material
is volcanic ejecta
violently blown out
of the volcano into
the atmosphere
during an eruption
It can be molten,
partially molten or
solid, with heated
gases
Basaltic Lava Types
A sampling of Hawaiian lava
A’a crumbles over an older
pahoehoe flow
Pahoehoe is “smoother” lava at the surface, while
A’a lava is a rougher more viscous rocky lava that
crumbles as it flows.
Projectile Volcanic Products
Ash, tephra, lava
bombs, lapilli, pele’s
tears, cinder,
pumice, and other
volcanic products
may be ejected
through the air.
Volcanic Bomb
Pyroclasts
Pyroclasts are classified by the size of the
particle
Volcanic ash is very fine dust which is “ash-like”
in consistency
Cinder is composed of gravel-sized pieces of
ejecta and usually feels rough to the touch
Volcanic bombs are large fragments of ejected
magma which become rounded and cool
(solidify) as they fly thru the atmosphere
Pyroclastic Flow
• For example,
eruption of
Vesuvius in 79
AD destroyed
the city of
Pompeii
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:
Naples
Vesuvius
Bay of
Naples
Courtesy of
www.swisseduc.ch
– 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!
Gases
Volcanoes can also eject
great quantities of gases
and steam which can be
mixed with the pyroclasts
Sulfur dioxide (SO2)
Hydrogen sulfide (H2S)
Carbon dioxide (CO2)
Hydrogen Chloride (HCl)
Hydrogen Fluoride (HF)
Lahar
Lahars are formed by the sudden mixing of
large volumes of pyroclastic material, such
as ash, with water
For example, when volcanic activity melts a
glacier on a mountain top, or because of
heavy rain, or the draining of a lake in a
crater
Lahar
Lahars can flow very fast, at speeds faster than
100 kilometers per hour (60 miles per hour)
They can flood large areas and flow for long
distances in river channels
Lahar in the Belham Valley, Montserrat, in the
Caribbean, during heavy rain, 19 July 2007
Nuée Ardente
A poetic-sounding French word introduced in
1904 to describe the terrible pyroclastic flow
that destroyed the entire city of St. Pierre on
the island of Martinique in 1902
It translates to “glowing incandescence”
Nuée Ardente
Nuée ardente are extremely fast moving
fluidized bodies of very hot gas, ash and rock
that hug the ground as they flow down the
volcanic slope
Temperatures can be as high as 800oC
Mount St. Helens
On May 18, 1980, at 8:32 am, a
magnitude 5.1 earthquake
occurred 1 mile directly under
the volcano
10 seconds later, the north
side of the volcano began to
collapse followed immediately
by an explosion that blew the
top 400 meters (1300 feet) off
of the peak (a volume of 1.3
cubic kilometers)
Mount St. Helens Ash Fall
Mount St. Helens
Mount St. Helens is
now a volcanic
national monument
and remains active
1902 Martinique
With each passing day,
the eruptions became
worse
The French governor
refused to evacuate the
city of St. Pierre and
surrounding smaller
cities at the base of the
volcano
On Wednesday, May 7, 1902, the governor with his
family and entourage visited St. Pierre
There was a gala ball that night
1902 Martinique
Martinique is an island
formed by volcanoes in
the Caribbean
It was a French colony
The dormant Mount Pelée
volcano began a new
series of eruptions on
April 25, 1902
1902 Martinique
The next day at 8:02 am,
the city of St. Pierre was
destroyed by a pyroclastic
flow that roared down the
slopes of Mount Pelée at of
670 kilometers per hour
(415 miles per hour)
1902 Martinique
Over 29,000 people
are burned alive in
seconds
The entire town was
completely destroyed
1902 Martinique
Supposedly, there was one lone survivor, LouisAuguste Cyparis (aka Ludger Sylbaris), who was
in jail either for murder or being drunk
He joined the circus
2007 Martinique
Today, Martinique is an overseas department of
France and St. Pierre is a quaint tourist attraction
Mount
Pele
Santorini
Santorini is a circular group
of islands in the Aegean
Sea and is part of Greece
The central lagoon is a
volcanic caldera 12 by 7
kilometers (8 by 4 miles) in
size
Mount Tambora
Mount Tambora (or Tomboro) is an active
stratovolcano on Sumbawa island, Indonesia
It was thought to be 14,000 feet (4,300 meters) high
when it blew up in April 1815
The death toll was at least 71,000 people (some
estimate 92,000 people were killed), of which
11,000 to 12,000 were killed directly by the eruption
Mount Tambora
The explosion was heard on Sumatra island
2,000 kilometers (1,200 miles) away
The red areas outlines the heavy ash fall
Year Without a Summer
1816 became known as the Year Without a
Summer and the Poverty Year and Eighteen
hundred and Froze to Death
Agricultural crops failed and livestock died in
much of the Northern Hemisphere, resulting in
the worst famine of the 19th century
Europe, still
recuperating from
the Napoleonic
Wars, suffered
from food
shortages