Transcript Unit 6 - Angelfire

Earth Formations &
Unusual Occurrences
Volcanoes
Volcanoes
• Volcanic landscapes contain diverse
landforms.
• The most recognizable of these
include volcano edifices, calderas,
and lava domes.
• Each of these landforms can vary
markedly in size, shape,
composition, and eruptive history.
When is a volcano considered active,
dormant, or extinct?
• _______________ – generally active or
showing activity through
earthquakes, uplift, or gas emissions
• _______________ – has the potential
or could erupt
• _______________ – typically cinder
cones since they usually only erupt
once
Parts of a Volcano
• _______________
– When an erupting volcano empties a
shallow-level magma chamber, the
edifice of the volcano may collapse into
the voided reservoir, thus forming a
steep, bowl-shaped depression called a
caldera
– These features are highly variable in
size, ranging from 1-100 km in
diameter.
• Crater Lake, Oregon
• Kilauea, Hawaii
• The Kilauea caldera is located at the
summit area of the Kilauea shield volcano
in Hawaii National Volcanic Park.
• It is shown here in a shaded elevation
map, courtesy of NASA. Kilauea caldera is
4 km in diameter.
• The U.S. Geological Survey's Hawaiian
Volcano Observatory lies on the high
northwest terrace of the caldera.
Lava Flows
• Two types
– _______________
– _______________
Pahoehoe
• Surfaces are
smooth, billowy,
or ropy
• ______________
flows typically
advance through
breakouts
beneath thin,
hardened crust
• Pahoehoe lavas
are typically the
first to erupt from
a vent
A’a Lava
• Flow fronts can
vary from 2 meters
to 20 meters thick.
• Pahoehoe is often
converted to a'a as
lava advances
down slope, away
from the volcano.
• Conversion of a'a
to pahoehoe never
takes place.
• Kilauea, Hawaii
Lava and Water
• Pahoehoe tends to pour into water in
a passive manner, sometimes with
little interaction beyond the boiling
of water.
• More explosive interactions are
generally associated with a'a flows.
• Water has a greater opportunity to
penetrate into the cracks of a'a,
where it expands explosively and
fragments the lava into airborne
particles.
• This passive entrance
of lava into the sea is
characteristic of most
pahoehoe lava.
• The hot lava has a
temperature between
1100 and 1150
degrees Celsius,
which results in the
instantaneous boiling
of the seawater.
• A’a lava
flowing into
the sea from a
cracking lava
tube.
Pyroclastic Flows
• A _______________is a fluid mixture of
solid to semi-solid fragments and hot,
expanding gases that flows down the flank
of a volcanic.
• These awesome features are heavier-thanair emulsions that move much like a snow
avalanche, except that they are fiercely
hot, contain toxic gases, and move at
phenomenal, hurricane-force speeds,
often over 100 km/hour.
• They are the most deadly of all volcanic
phenomena.
• Mt. Pelée,
Martinique
Mount St. Helens
• Mt. Augustine,
Alaska
– A pyroclastic flow
from the 1996
eruption of Mt.
Augustine
– The glowing
avalanche races
down the flanks of
the volcano at
hurricane-force
speeds.
– The avalanche is
partly disguised by
the more buoyant,
billowing ash cloud
that rises above it.
Eruptions
Fissure
Eruptions
Fire Fountains
• Pu’u O’o
Volcano Type
Volcano Shape
Eruption Type
Strombolian
CINDER CONE
Straight sides with steep slopes; large
summit crater
SHIELD VOLCANO
Hawaiian
Very gentle slopes; convex upward
COMPOSITE CONES
Plinian
Gentle lower slopes, but steep upper
slopes; concave upward; small summit
crater
Cinder Cones
• The most common type of volcano
• _______________ type of volcano –
usually less than 300 meters
• Parasitic cone on Mauna Kea
• Sunset Crater, Flagstaff, Arizona
Shield Volcanoes
• broad, low-profile features with
basal diameters that vary from a few
kilometers to over 100 kilometers
• Mauna Loa
Composite Cones
• are the most picturesque and the
most deadly of the volcano types
• Mt. Fuji, Japan
• Mount St. Helens (before)
• Mt. Etna is Europe's highest volcano at
10,900 ft (3,516 m).
• This SeaWiFS satellite image was taken on
Monday October 28 one day after Mt. Etna
began to erupt.
• The image is taken from the perspective
of looking across the Mediterranean Sea,
toward the west - Albania and Greece are
beneath Italy's "heel."
• The red arrows show the ash plume from
the eruption moving to the south.
Courtesy of NASA.
Historical Eruptions
• Mt. Pelée – 1902
• Population before eruption – 28,000
• Population after eruption - 2
Paricutin
• 1943 – 1952
• 200 miles west of Mexico City
• Not many people died from the
actual eruption.
Krakatau, Indonesia
• 1883
• Over 36,000 people died – mostly
from the tsunami that resulted
Mt. Pinatubo
• June 15, 1991
• Philippines
Mount St. Helens
• May 17, 1980
Mount St. Helens
• At 8:32 Sunday morning, May 18,
1980, Mount St. Helens erupted.
• Shaken by an earthquake measuring
5.1 on the Richter scale, the north
face of this tall symmetrical
mountain collapsed in a massive rock
debris avalanche.
• Nearly 230 square miles of forest was
blown over or left dead and standing.
• The eruption lasted 9 hours.
• The pyroclastic flow reached
temperatures of more than 1200ºF
The Bulge
• 08:27 (approximate) Pre-earthquake view of
the bulge on the volcano's north flank
produced by the growing cryptodome of
magma intruded since March 20. About 5
minutes later (08:32:11.4 PDT), a 5.1
magnitude earthquake struck beneath the
mountain at shallow depth.
• 08:32:47.0 Estimate of the time of the first photograph in
Rosenquist's sequence that shows movement of the
mountain. By this time, the first slide block had already
dropped about 2,300 feet and a second block behind it had
slid 330 feet. The beginning of the north flank's collapse
and downward movement to initiate the debris avalanche
was estimated to be 26 seconds earlier (08:32:21.0 PDT).
• 08:32:49.2 A little more than 2 seconds
later, as the slide blocks continued to
move, the initial explosions of the vertical
eruption column as well as the lateral
blast, although obscure, had already
begun.
• 08:32:53.3 The first slide block now had
dropped sufficiently to expose more of the
cryptodome magma, accelerating the
explosive expansion of gases in the magma
and the eruption of the first magmatic
material of the 1980 eruptions.
• 08:33:03.7 The continuing movement of the slide blocks and
explosions had now thoroughly "uncorked" the magmatic
system of the cryptodome, and old and new (magmatic) debris
were blasted outward by increasingly more powerful
explosions. The high-velocity lateral blast cloud, with its clearly
visible trajectory trails of large blocks, was overtaking the
slower moving debris avalanche.
• 08:33:18.8 Less than a minute after the start of the
debris avalanche, the eruption of Mount St. Helens
was in full fury, further enlarging the crater as
smaller slide blocks fell into the vent and were
blasted away. The leading front of the lateral blast
now had completely overtaken the debris avalanche.
• The lateral blast lasted no more than
30 seconds.
• Vertical column rose to 16 miles
within 15 minutes.
• Mudflows traveled
as fast as 30 mph,
carrying boulders as
large as 20 feet in
diameter.
• Ash fell as far away
as 930 miles
• 57 people died
Spirit Lake
• Spirit Lake was
dramatically
changed by the
debris avalanche.
This photo of Spirit
lake, with Mt.
Rainier in the
background, was
taken from the
summit of Mount St.
Helens in 1979.
• As the debris
avalanche slammed
into the south shore of
the lake, a wave
surged 600 feet up
nearby hillsides. Note
the scour marks on the
hillsides above the
lake.
• The avalanche raised
the level of the lake by
about 200 feet. It
raised the water
temperature to 96
degrees Fahrenheit.
• The May 18th eruption began when an
earthquake, magnitude 5.1 on the
Richter scale, jolted the volcano. This
caused the north flank of the mountain
to break loose. This enormous block slid
off the mountain at more than 100 miles
an hour. A second block collapsed behind
the first one. Then a third block broke
free. It was completely obscured by the
lateral blast.
• The blast of rocks, ash, and gases
swept across the land at speeds up to
670 miles an hour.
• Obscurity Lake
before and
after
• Spirit Lake
before and
after
Mudflow
• Reached up to 26 feet
• Location of ash
Tsunami
What is a tsunami?
• Tsunami is a
Japanese word
with the
English
translation,
"_____________
.“
How does a tsunami differ from
other waves?
• Tsunamis are not _______________
generated.
• A tsunami can have a wavelength of
up to 100 km and a period of up to
an hour.
• As a result of their long wavelengths,
tsunamis behave as shallow-water
waves.
• A wave becomes a shallow-water
wave when the ratio between the
water depth and its wave length gets
very small.
• In the Pacific Ocean, where the
typical water depth is about 4000 m,
a tsunami travels at about 200 m/s,
or over 700 km/hr.
• Because the rate at which a wave
loses its energy is inversely related
(the bigger the wave length the less
the loss of energy) to its wave
length, tsunamis not only spread at
high speeds, they can also travel
great, transoceanic distances with
limited energy losses.
• As a tsunami approaches land, it
begins to _______________and grow
in _______________.
• Despite losing some energy when
approaching shallow water, it still
has a tremendous amount when it
actually reaches the shore.
• Wave heights can be up to 10, 20, or
even 30 meters (30, 60, or 90 feet)
Aleutian Tsunami
• April 1, 1946
• Devastated Hawaii
• Originated near Alaska
Chilean Tsunami
• May 23, 1960
• Originated off the coast of Chile
• The 1960 tsunami had eight separate
waves that crested between 4 and 14
feet above sea level
• Destroyed the downtown area of
Hilo, Hawaii
Sumatra Tsunami
• December 26, 2004
• Was compared to the release of
energy of 23,000 Hiroshima-type
atomic bombs
• One of the most deadliest ever
tsunami
• Over 225,000 killed
Mountains
Mountains
• Mountains are formed by slow but
gigantic _______________ of the
earth's _______________.
• Sometimes the crust has folded and
buckled, sometimes it breaks into
huge blocks.
• Mountains make up about one-fifth of the world's
landscape.
• Heights of mountains are generally given as
heights above sea level.
• The world's highest peak on land is Mount Everest
in the Himalayas. It is 8,850.1728 m ( 29,036 ft )
tall.
• The world's highest mountain, from its base on
the ocean floor, is Mauna Kea, on Hawaii. It is
10,203 m ( 33,474 ft ) high but only 4,205 m (
13,796 ft ) is above sea level.
• The highest 14 mountains in the
world are all found in the Himalayas.
• The most famous being Mount
Everest.
• These mountains are growing at a
rate of 2.4 inches a year.
• Best & Worst Years on Mount Everest
– 1993, 129 summited and eight died (a
ratio of 16:1)
– 1996 – 98 summited and 15 died – a
ratio of 6 ½ : 1
• Panorama view from the Summit
– http://www.panoramas.dk/fullscreen2/full22.html
• Reaching the summit
– http://www.pbs.org/wgbh/nova/everest/exposure/