Earthquakes in the Western Colorado Plateau
The western Colorado Plateau in southeastern Utah is an area of low
seismicity, and historical earthquakes have generally been small
(M2-4) and widely distributed. The highest concentration of
seismicity is related to underground coal mining along the
northwestern edge of the western Colorado Plateau. Regional network
instrumentation in the Colorado Plateau outside the coal-mining area is
sparse, so the record, particularly for smaller earthquakes, may be
incomplete. Another part of the Colorado Plateau where induced
seismicity has occurred is the Rangely oil field in northwestern
Colorado, close to the Utah border, where earthquakes as large as M4.5
were triggered in the 1960s by fluid injection. The largest
historical earthquake in the Colorado Plateau in Utah was the 1988
M5.2 San Rafael Swell earthquake near Castle Dale south of Price.
However, larger earthquakes (M5-6) have occurred in northern Arizona.
Because moderate and large earthquakes are rare, expected levels of
strong ground shaking are relatively low. However, the stable,
undeformed bedrock at the ground surface over much of the Colorado
Plateau causes ground shaking to be felt and damage to occur over a
much larger area than for a similar magnitude earthquake in western
Utah. Ground shaking from the M5.2 San Rafael Swell earthquake near
Castle Dale was felt as far away as Golden, Colorado (475 km, 295
miles) to the east, but only as far as Delta, Utah (156 km, 97 miles)
to the west in the Basin and Range.
Faults
The
Colorado Plateau is a large, stable block of the North American tectonic
plate that extends across much of eastern Utah and western Colorado
and is characterized by generally flat-lying and locally folded
sedimentary rocks. It was uplifted relative to adjacent areas during
Cenozoic time, but is relatively unaffected by faulting in the past 2
million years. The most recent movement on geologically young faults
in the area is generally greater than 150,000 years and little
evidence exists for younger movement. Although the predominant mode
of deformation in the western Colorado Plateau is faulting on
northwest-trending faults in response to approximate northeast-southwest
stretching, data from the 1988 San Rafael Swell earthquake implies a
response to stretching in a roughly east-west direction, similar to
the tectonic stresses in the nearby Basin and Range and Intermountain
seismic belt to the west.
The few moderate-magnitude
earthquakes in the area have not been attributable to mapped
geologically young faults, and most earthquakes likely occur along
deeply buried pre-existing faults lacking surficial expression.
https://maps.google.com/maps?q=the+big+knoll+az&hl=en&client=firefox-a&ie=UTF-8&ei=lgvsUK29Bsv-2QWUwoCYAw&ved=0CAsQ_AUoAA
editor's whim:
Similar Dense Stone Outcroppings in the Middle of Nowhere.
Lacolith in Nature.
Volcanic Plug?
We need an Expert. We are not.
Too Similar IMHO.
I need to get some Sleep.
Stay Informed.
-MP
Devils Tower
From Wikipedia, the free encyclopedia
Devils Tower (
Lakota:
Matȟó Thípila or
Ptehé Ǧí, which means “Bear Lodge” and ”brown buffalo horn”, respectively) (
Arapaho: Wox Niiinon
[4]) is an
igneous intrusion or
laccolith located in the
Black Hills near
Hulett and
Sundance in
Crook County, northeastern
Wyoming, above the
Belle Fourche River. It rises dramatically 1,267 feet (386 m) above the surrounding terrain and the summit is 5,114 feet (1,559 m) above sea level.
Devils Tower was the first declared
United States National Monument, established on September 24, 1906, by President
Theodore Roosevelt. The Monument's boundary encloses an area of 1,347 acres (545 ha).
In recent years, about 1% of the Monument's 400,000 annual visitors
climb Devils Tower, mostly using
traditional climbing techniques.
[5]
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Name
Devils Tower in geological context. The oval-shaped mesa around the
Tower suggests the old volcano's shape. The red rock is the
Permian-Triassic Spearfish Formation, and above that is the younger,
white
Gypsum Springs Formation. Aerial photo, 2010.
Tribes including the
Arapaho,
Crow,
Cheyenne,
Kiowa,
Lakota, and
Shoshone
had cultural and geographical ties to the monolith before European and
early American immigrants reached Wyoming. Their names for the monolith
include: Aloft on a Rock (Kiowa), Bear's House (Cheyenne, Crow), Bear's
Lair (Cheyenne, Crow),
Daxpitcheeaasáao, "Home of bears" (
Crow[6]),
Bear's Lodge (Cheyenne, Lakota), Bear's Lodge Butte (Lakota), Bear's
Tipi (Arapaho, Cheyenne), Tree Rock (Kiowa), and Grizzly Bear Lodge
(Lakota).
The name Devil's Tower originated in 1875 during an expedition led by Col.
Richard Irving Dodge when his interpreter misinterpreted the name to mean Bad God's Tower, which then became Devil's Tower.
[7] All
information signs in that area use the name "Devils Tower", following a geographic naming standard whereby the apostrophe is eliminated.
[8]
In 2005, a proposal to recognize several
American Indian
ties through the additional designation of the monolith as Bear Lodge
National Historic Landmark met with opposition from the US
Representative
Barbara Cubin, arguing that a "name change will harm the tourist trade and bring economic hardship to area communities".
[9]
Geological history
Red sandstone and siltstone cliffs above the Belle Fourche River
Map of Wyoming National Parks and landmarks, showing Devils Tower (upper right) far east of
Yellowstone (upper left), north across the state from
Cheyenne.
The landscape surrounding Devils Tower is composed mostly of
sedimentary rocks. The oldest rocks visible in Devils Tower National Monument were laid down in a shallow sea during the
Triassic period, 225 to 195 million years ago. This dark red
sandstone and maroon
siltstone, interbedded with
shale, can be seen along the
Belle Fourche River.
Oxidation of iron minerals causes the redness of the rocks. This rock layer is known as the Spearfish Formation.
Above the Spearfish formation is a thin band of white
gypsum, called the
Gypsum Springs Formation. This layer of gypsum was deposited during the
Jurassic period, 195 to 136 million years ago.
Created as sea levels and climates repeatedly changed, gray-green
shales (deposited in low-oxygen environments such as marshes) were
interbedded with fine-grained sandstones,
limestones, and sometimes thin beds of red
mudstone. This composition, called the Stockade Beaver member, is part of the
Sundance Formation.
The Hulett Sandstone member, also part of the Sundance formation, is
composed of yellow fine-grained sandstone. Resistant to weathering, it
forms the nearly vertical cliffs which encircle the Tower itself.
About 65 million years ago, during the
Paleogene Period, the
Rocky Mountains and the
Black Hills were uplifted.
Magma rose through the
crust, intruding into the existing sedimentary rock layers.
[10]
Theories of formation
Geologists agree that Devils Tower was formed by the
intrusion of
igneous
material, but they cannot agree on how, exactly, that process took
place. Geologists Carpenter and Russell studied Devils Tower in the late
19th century and came to the conclusion that the Tower was formed by an
igneous intrusion. Later geologists searched for further explanations.
Several geologists believe the molten rock comprising the Tower might
not have surfaced; other researchers are convinced the tower is all that
remains of what once was a large explosive
volcano.
In 1907, scientists Darton and O'Hara decided that Devils Tower must be an eroded remnant of a
laccolith.
A laccolith is a large mass of igneous rock which is intruded through
sedimentary rock beds without reaching the surface, but makes a rounded
bulge in the sedimentary layers above. This theory was quite popular in
the early 20th century since numerous studies had earlier been done on
laccoliths in the Southwest.
Other theories have suggested that Devils Tower is a
volcanic plug
or that it is the neck of an extinct volcano. Presumably, if Devils
Tower was a volcanic plug, any volcanics created by it – volcanic ash,
lava flows, volcanic debris – would have been eroded away long ago. Some
pyroclastic material of the same age as Devils Tower has been
identified elsewhere in Wyoming.
The igneous material that forms the Tower is a
phonolite porphyry intruded about 40.5 million years ago,
[11] a light to dark-gray or greenish-gray igneous rock with conspicuous crystals of white
feldspar.
[12] As the magma cooled,
hexagonal (and sometimes 4-, 5-, and 7-sided)
columns
formed. As the rock continued to cool, the vertical columns shrank
horizontally in volume and cracks began to occur at 120 degree angles,
generally forming compact 6-sided columns. The nearby
Missouri Buttes,
3.5 miles (5.6 km) to the northwest of Devils Tower, are also composed
of columnar phonolite of the same age. Superficially similar, but with
typically 2 feet (0.61 m) diameter columns,
Devils Postpile National Monument and
Giant's Causeway are
columnar basalt.
Devils Tower did not visibly protrude out of the landscape until the overlying sedimentary rocks
eroded
away. As the elements wore down the softer sandstones and shales, the
more resistant igneous rock making up the tower survived the erosional
forces. As a result, the gray columns of Devils Tower began to appear as
an isolated mass above the landscape.
As rain and snow continue to erode the sedimentary rocks surrounding
the Tower's base, more of Devils Tower will be exposed. Nonetheless, the
exposed portions of the Tower still experience certain amounts of
erosion. Cracks along the columns are subject to water and ice erosion.
Erosion due to the expansion of ice along cracks and fractures within
rock formations is common in colder climates – a prime example being the
featured formations at
Bryce Canyon National Park.
Portions, or even entire columns, of rock at Devils Tower are
continually breaking off and falling. Piles of broken columns, boulders,
small rocks, and stones – or
scree – lie at the base of the tower, indicating that it was once wider than it is today.
[10]
Native American folklore
A sign informs visitors of the American Indian heritage.
According to the Native American tribes of the
Kiowa and Lakota
Sioux,
some girls went out to play and were spotted by several giant bears,
who began to chase them. In an effort to escape the bears, the girls
climbed atop a rock, fell to their knees, and prayed to the
Great Spirit
to save them. Hearing their prayers, the Great Spirit made the rock
rise from the ground towards the heavens so that the bears could not
reach the girls. The bears, in an effort to climb the rock, left deep
claw marks in the sides, which had become too steep to climb. (Those are
the marks which appear today on the sides of Devils Tower.) When the
girls reached the sky, they were turned into the star constellation the
Pleiades.
Another version tells that two
Sioux boys wandered far from their village when Mato the bear, a huge creature that had claws the size of
teepee poles, spotted them, and wanted to eat them for breakfast. He was almost upon them when the boys prayed to
Wakan Tanka
the Creator to help them. They rose up on a huge rock, while Mato tried
to get up from every side, leaving huge scratch marks as he did.
Finally, he sauntered off, disappointed and discouraged. The bear came
to rest east of the
Black Hills at what is now
Bear Butte. Wanblee, the eagle, helped the boys off the rock and back to their village. A painting depicting this legend by artist
Herbert A. Collins hangs over the fireplace in the visitor's center at Devils Tower.
In a
Cheyenne
version of the story, the giant bear pursues the girls and kills most
of them. Two sisters escape back to their home with the bear still
tracking them. They tell two boys that the bear can only be killed with
an arrow shot through the underside of its foot. The boys have the
sisters lead the bear to Devils Tower and trick it into thinking they
have climbed the rock. The boys attempt to shoot the bear through the
foot while it repeatedly attempts to climb up and slides back down
leaving more claw marks each time. The bear was finally scared off when
an arrow came very close to its left foot. This last arrow continued to
go up and never came down.
[13]
Wooden Leg,
a Northern Cheyenne, relates another legend told to him by an old man
as they were traveling together past the Devils Tower around 1866-1868.
An Indian man decided to sleep at the base of Bear Lodge next to a
buffalo head. In the morning he found that both himself and the buffalo
head had been transported to the top of the rock by the Great Medicine
with no way down. He spent another day and night on the rock with no
food or water. After he had prayed all day and then gone to sleep, he
awoke to find that the Great Medicine had brought him back down to the
ground, but left the buffalo head at the top near the edge. Wooden Leg
maintains that the buffalo head was clearly visible through the old
man's spyglass. At the time, the tower had never been climbed and a
buffalo head at the top was otherwise inexplicable.
[14]
The buffalo head gives this story special significance for the
Northern Cheyenne. All the Cheyenne maintained in their camps a sacred
teepee to the Great Medicine containing the tribal sacred objects. In
the case of the Northern Cheyenne, the sacred object was a buffalo head.
[15]
Recent history
Fur trappers may have visited Devils Tower, but they left no written
evidence of having done so. The first documented visitors were several
members of Captain W. F. Raynold's 1859
Yellowstone Expedition. Sixteen years later, Colonel
Richard I. Dodge escorted an Office of Indian Affairs scientific survey party to the massive rock formation and coined the name Devils Tower.
[16] Recognizing its unique characteristics,
Congress designated the area a U.S. forest reserve in 1892 and in 1906 Devil's Tower became the nation's first
National Monument.
[17]
The 1977 movie
Close Encounters of the Third Kind used the formation as a plot element and as the location of its climactic scenes.
[18][19] Its release was the cause of a large increase in visitors to the monument.
[20]
Volcanic plug
From Wikipedia, the free encyclopedia
A
volcanic plug, also called a
volcanic neck or
lava neck, is a
volcanic landform created when
magma hardens within a
vent on an active volcano. When forming, a plug can cause an extreme build-up of
pressure if
volatile-charged
magma is trapped beneath it, and this can sometimes lead to an explosive eruption. A good example is
Castle Rock (volcano), a volcanic plug that had volatile-charged magma still beneath it, leading to a
Volcanic Explosivity Index 2 eruption. If a plug is preserved,
erosion
may remove the surrounding rock while the erosion-resistant plug
remains, producing a distinctive upstanding landform. Examples include
Shiprock,
New Mexico;
Rockall,
The Nut,
Australia; the
Pitons of
Saint Lucia, and
Deganwy Castle,
Wales.
Glacial
erosion can lead to exposure of the plug on one side, while a long
slope of material remains on the lee side. Such landforms are called
crag and tail. An example is the
Castle Rock in
Edinburgh, Scotland.
Further examples of volcanic plugs in the
United States include
Morro Rock,
California;
Lizard Head,
Colorado; and
Laurel Hill,
New Jersey.
Devils Tower in
Wyoming, as well as
Little Devils Postpile located in Yosemite National Park, are also thought to be a volcanic plug by many
geologists. Another example of a volcanic plug in the eastern USA is the highly eroded
Stark's Knob basaltic structure located along the
Hudson River near
Saratoga Springs,
New York.
[citation needed] However, some geologists believe Stark's Knob is not a plug at all, but merely an outcrop of an ancient submarine lava flow.
Ailsa Craig,
Bass Rock,
North Berwick Law and
Dumgoyne hill are examples of volcanic plugs located in
Scotland.
Borgarvirki is a volcanic plug located in north Iceland. A volcanic plug is situated in the town of
Motta Sant'Anastasia in Italy.
New Zealand's Lion Rock was fortified as a refuge for local
Maori.
There are several volcanic plugs in New Zealand, including the Pinnacles in the
Coromandel Peninsula,
Bream Head, Paritutu and adjacent
Sugar Loaf Islands, and
Piha's Lion Rock, which hosted a fortified
Maori pa. Australia's
Mount Warning is a volcanic plug.
Another example is
Sigiriya (Lion's rock), the hardened magma plug from an extinct and long-eroded
volcano. The rock rises 370 m (1,210 ft) and is sheer on all sides, in many places overhanging the base.
[1] It hosts an ancient rock fortress and ruins of a castle, one of the eight
World Heritage Sites of Sri Lanka (Ref:202).
[2][3]
Another building on a volcanic plug is the 14th century
Trosky Castle in the Czech Republic.
The origin of the famous
Devils Tower (featured in the 1977 movie
Close Encounters of the Third Kind) in
Wyoming
(USA) is not totally clear. Although it is generally admitted that it
was formed by igneous intrusion, it is not necessarily a volcanic plug
(stricto censu) which formed within the vent of an active volcano.
Madtown Preppers Alerts are for informational use
only. These alerts purpose is to inform you of news events in order for
you to adjust your family preparedness programs. We believe that
knowledge is power and in order for you to make informed decisions, we
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inform you. We do not endorse any of the sources we link to in any
article.
*This is a theory. We are Truth Seekers, not Experts.*
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