earth formations & unusual occurrences. volcanoes
TRANSCRIPT
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-than-air 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
CINDER CONE
Straight sides with steep slopes; large summit crater
Strombolian
SHIELD VOLCANO
Very gentle slopes; convex upward
Hawaiian
COMPOSITE CONES
Gentle lower slopes, but steep upper slopes; concave upward; small summit crater
Plinian
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/