Transcript Hawai`i (Big Island)

Hawai‘i (Big Island)
Long-lasting Eruption of Kilauea Volcano, Hawai`i Leads to VolcanicAir Pollution
Kilauea
Summit
Hot Spot
1170°C
Erta` Ale
Divergent Plate
1130°C
Momotombo
Convergent
Plate
820°C
H0
37.1
77.2
97.1
C0
2
48.9
11.3
1.44
S0
2
11.8
8.34
0.50
H
0.49
1.39
0.70
CO
1.51
0.44
0.01
HS
2
0.04
0.68
0.23
HCl
0.08
0.42
2.89
HF
---
---
0.26
Volcano
Tectonic Style
Temperature
2
2
Profile of Hawaiian shield volcanoes compared with the profile of Mount
Rainier, one of the larger composite volcanoes of the Cascade Range,
drawn at the same scale.
Aerial view of some of the prominent fissures within the southwest rift
zone of Kilauea Volcano. The shiny dark lava was erupted from these
fissures in September 1971. (Photograph by J.D. Griggs.)
Growth profiles of Kilauea's newest volcanic cone, built during the Pu'u 'O'o eruption.
Map of the Big Island showing the volcanic hazards from lava flows.
Severity of the hazard increases from zone 9 to zone 1. Shaded areas
show land covered by historic flows from three of Hawaii's five
volcanoes (Hualalai, Mauna Loa, and Kilauea).
A’a Lava on top of Pahoehoe Flows
Pahoehoe Flows Dominate
Pahoehoe Flows Dominate Extrusive Igneous Rock - Lava (Hawaii)
Shiny strands of volcanic glass, called Pele's hair (above) are
commonly found downwind from active eruptive vents.
Volcanic spatter commonly becomes tightly welded to form
mounds around active vents (below). (Photographs by Donald
W. Peterson and Richard P. Moore, respectively.)
Graph illustrating the difference in average chemical compositions between lava
erupted by Hawaiian volcanoes and by Mount St. Helens in 1980. The number given
for each chemical element gives the amount (in weight percent) of that element
(expressed as oxide) contained in the lava. Left: Note the contrast in color and texture
between Hawaiian basalt (dark) and Mount St. Helens dacite (light).
The pyroclastic deposits exposed at Kilauea indicate that about two
dozen major explosive eruptions have occurred during the past 70,000
years. Mauna Loa apparently has had less frequent explosive eruptions
during the same time interval. Judging by their distribution and
thickness, Kilauea's prehistoric pyroclastic deposits had to be produced
by explosive eruptions at least as powerful as the 1790 eruption and, in
some cases, several times stronger.
Kilauea's explosions
Map showing areas covered by fallout from 4 explosions at Kilauea. This map is a work in
progress, and the question marks indicate areas where more observations are needed
Where can we see red lava? Currently, lava is flowing in a remote area of
the park, 3 miles beyond the ranger station at the end of Chain of Craters
Road:
Areas to the right (east) and seaward of the dotted lines are closed due to
the potential for major land collapse.
Methane Gas Explosions
Underground explosions occur
in front of lava flowing over
burning vegetation. Plants burn
in methane from soils without
oxygen as they are covered by
lava, creating methane gas
explosions. The gas fills
underground lava tubes. When
the methane ignites, the ground
explodes up to 100 yards/meters
in front of the advancing lava
flow. Rocks and debris blast in
all directions. DO NOT
APPROACH LAVA FLOWING
THROUGH VEGETATION!
When Lava Enters the Sea: Growth & Collapse of Lava Deltas
The new land where lava enters the ocean is poised to collapse without
warning. The area has been closed to the public. USGS 06/28/2005
The island of Hawai'i, known as the Big Island, is the largest in the Hawaiian Chain. Greater than
twice the area of the remaining main eight Hawaiian Islands combined, Hawai'i encompasses
10,432 sq km (4028 sq mi). The island was formed from five major volcanoes. The volcano of
Mauna Kea is the tallest mountain on Earth, reaching nearly 9 km (5.5 mi) from the seafloor to
the summit. Although shorter, Mauna Loa's massive size makes it the largest volcano in the
world. Kiluea, long thought to be part of Mauna Loa, is the only currently active subaerial
volcano in the Hawaiian Island chain and is home to Pele, the Hawaiian volcano goddess.
Kilauea is a shield volcano that rises approximately 6100 m
from the ocean floor and 1239 m above sea level. Its summit
area consists of a caldera that is 4 km long and 3.2 km wide.
This caldera formed by subsidence when magma was
withdrawn from beneath the summit (Stone 1926). The main
vent of Kilauea is a collapsed crater in the floor of the summit
caldera, called Halemaumau.
Until the 1959 eruption, the volcano had erupted about once
every 4 years.
Once considered a curiosity, explosions at Kilauea are now recognized as
an important type of eruption with significant hazard to people on the
ground and in the air. How did this revolution in thinking come about?
Deposits of tephra (anything solid exploded by a volcano) known as the
Keanakako`i Ash are a familiar sight at Kilauea's summit, particularly
southwest of the caldera, where the trade winds often blew ash during
eruptions. Geologists thought that the ash formed during eruptions in, or
within a few years before, 1790, when 80-800 people were killed. Some
older explosion deposits, such as the Uwekahuna Ash, were known but
had not been studied carefully.
In the late 1980s, Jocelyn McPhie, an Australian on a Fulbright
fellowship at UH-Manoa, studied the Keanakako`i Ash and found two ash
beds distributed southeastward, though most of the ash, slave to the trade
wind, went southwestward. She had no time to continue her work, but her
important discovery set the scene for what was to follow.
Kilauea is capable of exploding debris into the westerly jet
stream, which then transports the fallout into areas where
people live.
Small explosions, more numerous than the larger ones, may be
driven by groundwater. They may happen when the floor of
Halema`uma`u or of the caldera drops down to about the level
of the water table, more than 500 m (1,600 feet) deep. Such a
drop would serve as a warning that explosions, dangerous to
people in the summit but less so in outlying areas, could occur.
What drives such powerful explosions? Around 1,000-1,200
years ago, the largest explosion brought up rocks several
kilometers (miles) from the volcano's depths.
This explosion was likely caused by rapid expansion of carbon
dioxide bubbles within Kilauea's deep plumbing system. Were
the Keanakako`i explosions also driven by CO2? What is the
interplay between gas from the magma and steam from
groundwater? These and other questions will take time to
answer.
Glowing lava flows erupt from vents on the south flank of the Pu‘u ‘O‘o
cone. Ongoing collapse of the southwest (left) side of the cone has
formed a scallop-shaped scar, revealing red layers of welded spatter
(deposited as clots of molten lava) that underlie loose tan-colored cinders
(bubble-filled, glassy lava pieces that solidified while still airborne).
(USGS photo by Richard Hoblitt, January 2004.)
During the first 3½ years of the
eruption, fallout from lava fountains
at Pu‘u ‘O‘o built a cinder-andspatter cone 835 feet (255 m) high,
more than twice as high as any
other cone on Kilauea’s east rift
zone. Cone growth ceased after the
activity shifted to Kupaianaha in
mid-1986. When the eruption
returned to Pu‘u ‘O‘o in 1992, lava
flows from flank vents built a
“shield” against the west flank of
the cone (top). In 1993, collapse
pits appeared on the west flank of
Pu‘u ‘O‘o as subsidence over the
flank vents undermined the cone.
When the crater floor dropped in
January 1997, the weakened flank
also failed, leaving the prominent
“west gap.” Note growth of the
shield (bottom). (USGS photos by
Tari Mattox and Christina Heliker.)
Kilauea's south flank is moving seaward at up to three inches per year. This area experienced a
magnitude 7.2 earthquake in 1975; it is also where the most spectacular palis (the Hawaiian word
for cliffs) are found. The southeast flank of Mauna Loa is also moving seaward, but at a slower
rate. This region of Mauna Loa experienced a magnitude 6.7 earthquake in 1983. Although these
motions are a small fraction of those that occurred during the earthquakes, they indicate that the
forces that produced the earthquakes and created the palis are still active.
ERUPTION STATISTICS 1983 TO 2004
Lava flows
• Area covered: 45.1 square miles (116.9 km2)
• New land: 560 acres (225 ha)
• Volume: 0.6 cubic miles (2.6 km2)
• Thickness along coast: 33 to 115 feet (10-35 m)
• Coastal highway covered: 8.9 miles (14.3 km)
• Structures destroyed: 189
Pu‘u ‘O‘o
• Maximum height, 1987: 835 feet (255 m)
• Height, February 2004: 595 feet (181 m)
• Crater size: 820 x 1,312 feet (250 x 400 m)