Hilina Slump
Encyclopedia
The Hilina Slump is a 5,000 cubic mile (20,000 kilometre³) chunk of the big island
of Hawaii
on the south flank of the Kilauea
volcano
. Between 1990 and 1993, Global Positioning System measurements showed a southward displacement of the south flank of Kilauea
up to approximately 10 centimeters per year. The slump has the potential of breaking away at a faster pace in the form of an underwater landslide
. In Hawaii, landslides of this nature are called debris avalanches. If the entire Hilina Slump did slide into the ocean at once, it could cause an earthquake
in excess of a 9 in magnitude and a megatsunami
. Previous megatsunamis in Hawaii 110,000 years ago caused by similar geological phenomena created waves 1,600 feet (500 m) tall. Were such a megatsunami to occur again, it would threaten the entire Pacific Rim
.
On April 2, 1868, an earthquake
in this area with a magnitude estimated between 7.25 and 7.75 rocked the southeast coast of Hawaii. It triggered a landslide on the slopes of the Mauna Loa
volcano
, five miles (8 km) north of Pahala
, killing 31 persons. A tsunami claimed 46 additional lives. The villages of Punaluu, Ninole, Kawaa, Honuapo, and Keauhou Landing were severely damaged. According to one account, the tsunami "rolled in over the tops of the coconut trees, probably 60 feet (20 m) high ... inland a distance of a quarter of a mile in some places, taking out to sea when it returned, houses, men, women, and almost everything movable."
On November 29, 1975, a 40 mile (60 km) wide section of the Hilina Slump plunged 11 feet (3 m) into the ocean, widening the crack by 26 ft (8 m). This movement caused a 7.2 magnitude earthquake and a 50 foot (15 m) high tsunami. Oceanfront properties were washed off their foundations in Punaluu. Two deaths were reported at Halape, and 19 other persons were injured. The shoreline at Keauhou Bay
was dramatically altered.
It is predicted that the Hilina slump is sliding seaward on top of the southern flank of the Kilauea volcano that composes the southeastern portion, about 13.7%, of the Big Island of Hawaii. Compared to the 25,000 to 35,000 km3 volume of Kilauea, the submarine slide is between 10,000 to 12,000 km3, making up about 10% of the island. Model results based on present day slope and sea level suggest that earthquake accelerations stronger than about 0.4 to 0.6 g are enough to exceed the static friction coefficient resulting in a slip along a failure surface. However, recent undersea measurements show that an undersea "bench" has formed a buttress at the forefront of the Hilina Slump, and "this buttress may tend to reduce the likelihood of future catastrophic detachment."
As the Pacific plate is being pushed to the west/northwest, it is traveling over a hot spot that is erupting silica poor and highly viscous basaltic magma. The Big Island of Hawaii is the youngest of the chain of Hawaiian shield volcanoes that have penetrated and scarred the overriding Pacific plate. Located on the eastern side of the Big Island, the Kilauea volcano is believed to be the only Hawaiian volcano still being fed by the magma chambers below. Since the northeastern flank of the Hilina slump is still growing, the sliding southern flank of the slump may be experiencing a frictional force that is resisting slope failure as the northeastern flank is pushing upwards. Once the northeastern flank becomes inactive, and the resisting frictional force decreases, the Hilina slump may be more susceptible to submarine landslides caused by earthquakes.
Hawaii (island)
The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
of Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
on the south flank of the Kilauea
Kilauea
Kīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
. Between 1990 and 1993, Global Positioning System measurements showed a southward displacement of the south flank of Kilauea
Kilauea
Kīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
up to approximately 10 centimeters per year. The slump has the potential of breaking away at a faster pace in the form of an underwater landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
. In Hawaii, landslides of this nature are called debris avalanches. If the entire Hilina Slump did slide into the ocean at once, it could cause an earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
in excess of a 9 in magnitude and a megatsunami
Megatsunami
Megatsunami is an informal term to describe a tsunami that has initial wave heights that are much larger than normal tsunamis...
. Previous megatsunamis in Hawaii 110,000 years ago caused by similar geological phenomena created waves 1,600 feet (500 m) tall. Were such a megatsunami to occur again, it would threaten the entire Pacific Rim
Pacific Rim
The Pacific Rim refers to places around the edge of the Pacific Ocean. The term "Pacific Basin" includes the Pacific Rim and islands in the Pacific Ocean...
.
On April 2, 1868, an earthquake
1868 Hawaii earthquake
The 1868 Hawaii earthquake is the largest recorded in the history of Hawaii island, causing a landslide and tsunami that led to 77 deaths. The earthquake occurred at 4 p.m. local time on April 2, 1868...
in this area with a magnitude estimated between 7.25 and 7.75 rocked the southeast coast of Hawaii. It triggered a landslide on the slopes of the Mauna Loa
Mauna Loa
Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...
volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
, five miles (8 km) north of Pahala
Pahala, Hawai'i
Pahala is a census-designated place in Hawaii County, Hawaii, United States. The population was 1,378 at the 2000 census.-Geography:Pahala is located at ....
, killing 31 persons. A tsunami claimed 46 additional lives. The villages of Punaluu, Ninole, Kawaa, Honuapo, and Keauhou Landing were severely damaged. According to one account, the tsunami "rolled in over the tops of the coconut trees, probably 60 feet (20 m) high ... inland a distance of a quarter of a mile in some places, taking out to sea when it returned, houses, men, women, and almost everything movable."
On November 29, 1975, a 40 mile (60 km) wide section of the Hilina Slump plunged 11 feet (3 m) into the ocean, widening the crack by 26 ft (8 m). This movement caused a 7.2 magnitude earthquake and a 50 foot (15 m) high tsunami. Oceanfront properties were washed off their foundations in Punaluu. Two deaths were reported at Halape, and 19 other persons were injured. The shoreline at Keauhou Bay
Keauhou Bay
Keauhou Bay is a historic area in the Kona District of the Big Island of Hawaii.The name comes from ke au hou which means "the new era" in the Hawaiian Language.-Kamehameha III's Birthplace:...
was dramatically altered.
It is predicted that the Hilina slump is sliding seaward on top of the southern flank of the Kilauea volcano that composes the southeastern portion, about 13.7%, of the Big Island of Hawaii. Compared to the 25,000 to 35,000 km3 volume of Kilauea, the submarine slide is between 10,000 to 12,000 km3, making up about 10% of the island. Model results based on present day slope and sea level suggest that earthquake accelerations stronger than about 0.4 to 0.6 g are enough to exceed the static friction coefficient resulting in a slip along a failure surface. However, recent undersea measurements show that an undersea "bench" has formed a buttress at the forefront of the Hilina Slump, and "this buttress may tend to reduce the likelihood of future catastrophic detachment."
As the Pacific plate is being pushed to the west/northwest, it is traveling over a hot spot that is erupting silica poor and highly viscous basaltic magma. The Big Island of Hawaii is the youngest of the chain of Hawaiian shield volcanoes that have penetrated and scarred the overriding Pacific plate. Located on the eastern side of the Big Island, the Kilauea volcano is believed to be the only Hawaiian volcano still being fed by the magma chambers below. Since the northeastern flank of the Hilina slump is still growing, the sliding southern flank of the slump may be experiencing a frictional force that is resisting slope failure as the northeastern flank is pushing upwards. Once the northeastern flank becomes inactive, and the resisting frictional force decreases, the Hilina slump may be more susceptible to submarine landslides caused by earthquakes.