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 |
Visit A Volcano - Hawaii National Parks and Monuments
Learn More About
Shield Volcanoes
Learn More About
Plate Tectonics and "Hot Spots"
For More Hawaii Volcano Information
Link to:
Hawaii Volcano Observatory Website
Hawaii:
Hawaiian Islands:
Excerpts from: Wood and Kienle, 1990, Volcanoes of North America: Cambridge University Press, contribution by Charles A. Wood; and USGS Hawaii Volcano Observatory Website, 2001 |
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| Hawaiian "Hot Spot" |
Hawaiian "Hot Spot":2
Over the past 70 million years, the combined processes of magma formation,
volcano eruption and growth, and continued
movement of the Pacific Plate over the stationary Hawaiian "hot-spot"
have left a long trail of volcanoes across the Pacific Ocean
floor. The Hawaiian Ridge-Emperor Seamounts chain extends some 6,000 kilometers
from the "Big Island" of Hawaii to the Aleutian
Trench off Alaska. The Hawaiian Islands themselves are a very small part of
the chain and are the youngest islands in the
immense, mostly submarine mountain chain composed of more than 80 volcanoes.
The length of the Hawaiian Ridge segment
alone, from the Big Island northwest to Midway Island,
is about equal to the distance from Washington, D.C. to Denver,
Colorado (2,600 kilometers). The amount of lava erupted to form the
Hawaiian-Emperor chain is calculated to be at least 750,000
cubic kilometers-more than enough to blanket the entire
State of California with a layer of lava roughly 1.5 kilometers thick.
| Diamond Head State Monument |
Diamond Head:
Hawai'i's most famous landmark --
a large tuff cone which was formed
by a short series of explosive
eruptions some 100,000 years ago;
National Natural Landmark.
Picnicking on the crater floor in a
landscaped meadow; detachment from the city.
Moderate family hike (bring a flashlight)
with panoramic
view of Honolulu; trail 0.7 mile one-way
and with some hazards.
Viewpoint of Kahala plain. Park gate
open 6 a.m. to 6 p.m.
How the Crater was Formed:8
The pronounced seaward summit, deeply eroded
ridges, and ovoid-shaped crater are evidence
of Le'ahi's (Diamond Head)
very dynamic geological history.
The creation of O'ahu began around 2.5 to 3
million years ago with volcanic eruptions
from 2 shield volcanoes. A period of
extensive erosion followed, leaving the
Ko'olau and Wai'anae Mountain Ranges as the
remnants of these very eroded volcanoes.
After about 2 million years of volcanic
inactivity, the southeastern end of the
Ko'olau Range erupted. These eruptions
occurred near the ocean where the magma was
broken down into ash and fine particles by
the water and steam. Blown into the air,
these particles were cemented together into
a rock called tuff which created tuff cones,
such as Le'ahi.
Le'ahi is believed to have been created
about 300,000 years ago during a single,
brief eruption. The broad, saucer-shaped
crater covers 350 acres with its width being
greater than its height. The southwestern
rim is highest because winds were blowing
ash in this direction during the eruption.
Since the eruption, the slopes of the crater
have been eroded and weathered by rain,
wind, and the pounding of the sea. A coral
reef now protects the seaward slopes of the
crater.
Today, Le'ahi is the most
recognized landmark in Hawai'i. It was
designated a National Natural Landmark in
1968 as an excellent example of a tuff cone.
| Haleakala National Park |
Haleakala:4
Haleakala is the easternmost of two shield volcanoes
forming the island of Maui (more than 830,000 years ago),
and is the third largest of all Hawaiian shield volcanoes,
having a total volume of approximately 29,300 cubic kilometers.
Haleakala Crater:4,5
Haleakala Crater is now a cool, cone-studded reminder of a once-active volcano.
Streaks of red, yellow,
gray, and black trace the courses of recent and ancient lava, ash, and cinder flows.
The volcanic rocks
slowly break down as natural forces reduce them to minute particles which are
swept away by wind, heavy
rain, and intermittent streams.
The only known historical eruption
at Haleakala (1790 A.D. +/- 3 years)
occurred near La Perouse Bay and was witnessed by Hawaiians.
Lava Flows and Cinder Cones:4
Lava Flows and cinder cones (up to 180 meters high)
completely cover the floor of Haleakala Crater.
| Hawaii Volcanoes National Park |
Hawaii Volcanoes National Park:6
Today Hawaii Volcanoes National Park displays the results of
70 million years of volcanism, migration,
and evolution - processes that thrust a bare land from the sea and clothed it with complex and unique
ecosystems and a distinct human culture. Created to preserve the natural setting of Kilauea and Mauna
Loa, the park is also a refuge for islands native plants and animals and a link to its human past.
Kilauea, Mauna Ulu, and Pu'u O'o:7
Written records of
Kilauea's activity began with arrival of Christian missionaries in 1823.
The following century saw nearly
continuous eruption in the caldera,
punctuated by lava-lake subsidence and eruptions along both rift zones.
Continuous summit activity ended in 1924 with deep subsidence and an explosive eruption at Halemaumau.
Eruptions occurred intermittently in Halemaumau through 1934 and, following a hiatus, resumed in 1952.
Eruptions returned to the east rift zone in 1955, and were frequent on both summit and flank until 1968;
but in 1969 summit eruptions became less frequent as sustained activity began along the east rift zone.
That activity so far has built lava shields and extensive flow fields and pyroclastic deposits at Mauna Ulu
(1969-1974) and Pu'u O'o (beginning in 1983).
| Kilauea Volcano |
Kilauea Volcano:3
When Kilauea began to form is not known, but various estimates are
300,000-600,000 years ago. The volcano has been active ever since, with no
prolonged periods of quiescence known. Geologic studies of surface exposures,
and examination of drillhole samples, show that Kilauea is made mostly of lava
flows, locally interbedded with deposits of explosive eruptions. Probably what we
have seen happen in the past 200 years is a good guide to what has happened ever
since Kilauea emerged from the sea as an island perhaps 50,000-100,000 years
ago.
Kilauea and Halemaumau:7
Kilauea lies at the southeast end of the Hawaiian chain. It is the youngest major
shield now protruding
above sea level, but much of its bulk is under water. The subaerial part of Kilauea covers approximately
1,500 square kilometers. Its modern caldera
contains an annulus of arcuate blocks stepped downward toward
an inner sink, which is partly filled by a lava shield indented by Halemaumau crater. The modern caldera
is thought to be nested within the buried rim of an older caldera. Two rift zones radiate from the summit.
Kilauea probably began to grow
about 200,000 years ago, and the oldest flows of Hilina Basalt now exposed in the fault scarps of
the subaerial south flank probably date from 50-100 thousand years ago.
| Mauna Loa |
Mauna Loa and Mokua'aweoweo:7
Mauna Loa is considered the world's largest active volcano, with an estimated volume of more than 40,000
cubic kilometers, based on the assumption that the volcano extends from the surface to the top of the
isostatically depressed ocean crust. However, because of adjacent volcanoes interfingering with Mauna Loa,
and because older volcanic edifices may be buried at depth, the volcano's actual volume is probably less.
The Mauna Loa shield
is composed entirely of relatively thin flows of aa and pahoehoe, averaging 3 to 4
meters in thickness. Individual flows are typically less than one kilometer wide, but some are greater
than 50 kilometers long. Mauna Loa's summit is indented by a 3 x 5-kilometer
caldera up to 180 meters
deep -- Mokua'aweoweo. ... Mauna Loa's summit -- elevation of 4,619 meters above sea level, and
approximately 9 kilometers above the seafloor) -- is usually snow-covered in winter months.
Excerpts from:
1) Wood, 1990, IN: Wood and Kienle, 1990,
Volcanoes of North America:
Cambridge University Press
2) Kious and Tilling, This Dynamic Earth: The Story of Plate Tectonics:
USGS Online Publication
and
3) USGS Hawaii Volcano Observatory Website, January 2001
4) West, 1990, IN: Wood and Kienle, 1990,
Volcanoes of North America:
Cambridge University Press
5) U. S. National Park Service Website,
Haleakala National Park, 2000
6) U. S. National Park Service Website,
Hawaii Volcanoes National Park, Hawaii, 2000
7) Wood, Lockwood, and Holcomb, 1990, IN: Wood and Kienle, 1990,
Volcanoes of North America:
Cambridge University Press
8) State of Hawaii, Department of Land and Natural Resources
Website, 2002
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