America's Volcanic Past
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| "Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994 |
Select Volcanic Highlights and Features:
| [NOTE: This list is just a sample of various Craters of the Moon features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of the Craters of the Moon.] |
Craters of the Moon Lava Field:
Excerpt from: NASA "Earth From Space" Website, 2002 |
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| Craters of the Moon Lava Field |
Craters of the Moon Lava Field:4
The Craters of the Moon Lava Field is the largest
basaltic, dominantly Holocene (last 10,000
years) lava field in the conterminous United States.
Volcanic eruptions first occurred at
Craters of the Moon about 15,000 years ago.
The most recent eruptions ended about 2,100
years ago and were likely witnessed by the
Shoshone people. A Shoshone legend speaks of
a serpent on a mountain who,
angered by lightening, coiled around and
squeezed the mountain until liquid rock flowed,
fire shot from cracks, and the mountain exploded.
The volcanic area now lies dormant,
but its eight eruptive periods formed
60 lava flows which traveled as far as
45 miles from their vents.
Some of the lava flowed around areas
of higher ground, forming isolated
islands of vegetation called "kipukas".
Today, these kipukas provide a
window on the vegetation communities of
the past. They contain some of
the last pristine vegetation in the
Snake River Plain, including 700-year-old
juniper trees and relic stands of
sagebrush and native bunchgrass.
| Craters of the Moon National Monument |
Craters of the Moon National Monument1
Established in 1924, Craters of the Moon National
Monument celebrated its 75th birthday in 1999. On
November 9, 2000, President Clinton issued a
proclamation greatly expanding the size of the
monument. The expanded monument will be
managed cooperatively by the National Park Service
and the Bureau of Land Management. The
monument encompasses three major lava fields
and the surrounding sagebrush steppe
grasslands. The Craters of the Moon lava field
covers 618 square miles and is the largest young
basaltic lava field in the conterminous United
States. The park contains more than 25 volcanic
cones including outstanding examples of spatter
cones. Sixty lava flows lie within the Craters of the
Moon lava field ranging in age from 15,000 to just
2,000 years old. The Kings Bowl and Wapi lava
fields, which are about 2,200 years old, are now
part of the monument. All three lava fields lie along
the Great Rift, with some of the best examples of
open rift cracks in the world. There are excellent
examples of pahoehoe, slabby pahoehoe, shelly
pahoehoe, spiny pahoehoe, aa, and block lava, as
well as rafted blocks, tree molds, lava tubes, and
many other volcanic features. Although a desolate
looking place at first glance, the Monument thrives
with wildlife. A 7 mile loop drive at the north end of
the Monument provides unique views and hiking
opportunities.
Big Cinder Butte:2
Big Cinder Butte - the highest cone within the monument - has a total
volume of 2 x 108 cubic meters and rises 250 meters above the
plain. It has no summit crater. Many bombs are found on the cone,
including cow dung, breadcrust, and spindle types. The rims of five or
six older volcanoes are visible around its base. Several flows issued
from Big Cinder Butte. The youngest originated from a fissure on the
north side of the cone and is a "Blue Dragon" types pahoehoe flow. This
type of flow is characterized by a shining iridescent surface.
Big Craters:2
Big Craters is a series of spatter cones and open fissure flows.
The slope of each cone is 50 to 60 degrees near the summit and decreases
to approximately 30 degrees near the base. The upper slopes are angular
and rough, but the lower slopes are smoother and have profiles similar to
those of cinder cones. The cones range in height from 12 to 20 meters and
have chimneylike vent areas, most of which have collapsed, displaying a
rubbly interior. Toward the northwest portion of the Big Crater area,
however, two vents remain intact. Several large pahoehoe and aa flows
were erupted from these vents.
Devil's Orchard:1
After the road skirts Paisley Cone,
on the east side stands Devils Orchard. This group of
lava fragments stands like islands in a sea of cinders.
A short spur road leads to a self-guiding trail through
these weird features. As you walk this 1/2-mile trail,
you will see how people have had an impact on this lava
landscape and what is being done to protect it today.
This barrier-free trail is designed to provide access to
all people.
Great Rift:4
The monument's central focus is the Great Rift,
a 62-mile long crack in the earth's crust.
The Great Rift is the source of a remarkably
preserved volcanic landscape with an
array of exceptional features. Craters, cinder cones,
lava tubes, deep cracks, and
vast lava fields form a strangely beautiful
volcanic sea on central Idaho's Snake River Plain.
MORE Great Rift:5
The Great Rift volcanic rift zone is a zone of cracks
running approximately northwest to southeast across
almost the entire eastern part of the
Snake River Plain.
The entire Great Rift is 62 miles long.
The Great Rift is an example of basaltic
fissure eruption. This type of volcanic
activity is characterized by extrusion of
lavas from fissures or vents that is relatively
quiet in comparison with highly explosive
eruptions such as the 1980 Mount Saint
Helens eruption.
Where the Great Rift intersects the earth's
surface, there is an array of cinder cones,
lava cones, eruptive fissures, fresh-appearing
lava flows, noneruptive fissures, and
shield volcanoes.
Highway Flow:2
The North Crater flow possesses features termed "monoliths" which appear to
be fragments of cinder cones broken apart and rafted to their present
positions by flowing lava. They range in length from about 1/2 to 200
meters long; some are up to 25 meters high. The massive Highway flow
issued northward from North Crater vent and was confined to the valley
between Sunset and Grassy Cones.
Indian Tunnel:2
Indian Tunnel is one of the largest lava tubes in the Monument,
reaching widths of over 15 meters.
Concentric rock heaps in this area were probably
used to secure tepees of the Indians who
frequented the caves. Numerous other tunnels and
caves are common in this area, ranging from
centimeters to meters in size.
Inferno Cone:2
The area east of Inferno Cone consists of a series of lava "domes". Many
of the flow unites contain lava tubes, and individual flow units are
generally "Blue Dragon" pahoehoe. The lava tubes in this area may be part
of an extensive network in a single flow. Indian Tunnel is one of the
largest tubes in the Monument. [See Indian Tunnel above]
King's Bowl:3
Composite flow field; Basalt composition; 1,500 meter elevation.
The King's Bowl Field is small and cover less than 2.6 square kilometers.
It is situated on the King's Bowl Rift Set, one of several such sets which
collectively make up Idaho's Great Rift, a series of tension fractures
that cross cut the eastern Snake River Plain. The King's Bowl field is a
composite feature made up of flows from several point sources along the
Rift as well as a larger, apparently dike-fed sheet flow, which for a time
was held in a lava lake. These flows locally overlap, indicating that the
eruptive sequence was complex and issued from different vents at different
times.
North Crater:2
The North Crater flow possesses features termed "monoliths" which appear to
be fragments of cinder cones broken apart and rafted to their present
positions by flowing lava. They range in length from about 1/2 to 200
meters long; some are up to 25 meters high. The massive Highway flow
issued northward from North Crater vent and was confined to the valley
between Sunset and Grassy Cones.
Picabo Volcanic Field:4
Craters of the Moon is in the Picabo Volcanic Field.
Sunset and Grassy Cones:2
Sunset and Grassy cones rise approximately 160 meters above the
surrounding plain. Three flows issued from Sunset cone but are largely
blanketed with ash and soil. Two pahoehoe flows breached the crater in
the northeast and in the west. On the northwest flank of the crater, an
aa flow, approximately 6 meters thick issued from a small parasitic cone.
Both cones represent some of the earliest eruptive activity in the
Monument. Two craters on the north side of Grassy Cone erupted lava
simultaneously to produce flows which merged and extended northward. A
network of lava tubes, some as large as 5 meters in diameter, developed
within the flows.
Wapi:2
The Wapi lava field is one of several Holocene to Pleistocene volcanic
fields on the Snake River Plain. In many respects, it is typical of the
older fields of low shields that make up the present surface of the plain.
It covers a large (300 square kilometer) area that is elongate in the
north-south direction and has three prominent lobes extending east, west,
and northwest from the main mass of the field.
| Snake River Plain |
Snake River Plain:1
Craters of the Moon lies at the north
edge of the eastern Snake River
Plain, a broad flat arc, concave to the
north, which covers nearly 10,000
square miles of southern Idaho. It
extends from the Yellowstone Plateau
and the Teton Mountains on the east
to the Oregon state line on the west.
The Snake River borders the southern
edge of the plain, which occupies
almost a quarter of the surface of Idaho and
contrasts markedly with the mountainous
terrain that dominates the northern, central,
and far southern parts of the state.
The eastern Snake River Plain is essentially flat in
this vicinity: vertical relief is a few
hundred feet at Craters of the Moon and less than
that elsewhere.
| MORE America's Volcanic Past - Idaho |
Excerpts from:
1) U.S. National Park Service Website,
Craters of the Moon National Monument, 2000
2) Greeley, 1990, IN: Wood and Kienle, 1990,
Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p
3) King, 1990, IN: Wood and Kienle, 1990,
Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p
4) U.S. Bureau of Land Management, Idaho Office, Website, 2001
5) NASA "Earth From Space" Website, 2002
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