Hilina Slump - Hawaii's 2012?

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The Hilina Slump is a 4,760 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.^[1] 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 (487 m) tall.^[2] 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 (18 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."^[3]

On November 29, 1975, a 37 mile (60 km) wide section of the Hilina Slump plunged 11 feet (3 m) into the ocean, widening the crack by 26 feet (7.9 m). This movement caused a 7.2 magnitude earthquake and a 48 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.

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.^[4] 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. ^[5] 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."^[6] ^[7]

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 cause by earthquakes.^[8]

Hualalai Eruptive Activity

Hualalai is the third youngest of the volcanos making up the Big Island. It towers above above Kailua-Kona, and its steep slopes form the backdrop for the city. The most recent eruption of Hualalai Volcano occured in 1801 and covered an area shown on the map on the left. The character of this eruption was reported by John Young a form member of Captain Cook's crew and advisor to King Kamehameha I. Lava issued from two vents along the Northwest Rift Zone, with the upper being the first as is often the case on Mauna Loa's rift zones. Hualalai is in its Post-tholeitic, alkalic phase, and it is puzzling why the rift zones are still a preferred site of eruptive activity. Apparently its shallow magma chamber has essentially cooled, and the eruption seems to have come from a depth exceeding 10 km. The evidence for this is the unusual xenoliths (foreign rocks) that were piled near the vent. Many of these were dunites, which as you will recall are formed at the bottom of magma chambers. The fact that these rocks were brought to the surface seems to indicate that lava rose rapidly from below this depth. Also, the lava covering the xenoliths is frothy with large bubbles, seemly having a much high volatile content than is generally found in vesiculated, surface erupted lavas. The lava must of risen rapidly to the surface to carry such a large load of such dense xenoliths

1801 Hualalai eruption Many people think of Hualalai as a dead or extinct volcano, although this is hardly the case. Over half of the surface lavas of Hualalai are younger than 3,000 years, and about 25 percent of the surface was covered by lava erupted later than 1000 A.D. The map on the right shows the age distribution of recent prehistorical flows on Hualalai volcano. Lighter shades represent younger lava, with the lightest less than 1000 years old, and the darkest shown greater than 10,000 years old. You will probably have to expand this view (click on image) to see the details of these flows. Again, as with the 1801 eruption, it seems that most flows erupt along the rift zone. Apparently Hualalai erupts every few centuries, the last time being in 1801. A swarm of large earthquakes beneath Hualalai in 1929 has been interpretted by many as an intrusion or dike that did not make it to the surface. Unfortunately, the availablility of seismic data at that time was not adequate to be definitive on this matter. Still, because of the steep slopes and fairly frequent eruptions, Hualalai poses a distinct threat to Kailua-Kona and agent communities. See more at http://www.uhh.hawaii.edu/~kenhon/GEOL205/maunaloa/default.htm

Yellowstone Hot Spot Shreds Ancient Pacific Ocean

Analysis by Michael Reilly
Thu Sep 2, 2010 05:15 PM ET
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If you thought the geysers and overblown threat of a supervolcanic eruption in Yellowstone National Park were dramatic, you ain't seen nothing: deep beneath Earth's surface, the hot spot that feeds the park has torn an entire tectonic plate in half.

The revelation comes from a new study in the journal Geophysical Research Letters that peered into the mantle beneath the Pacific Northwest to see what happens when ancient ocean crust from the Pacific Ocean runs headlong into a churning plume of ultra-hot mantle material.

Geologically speaking, the Pacific Northwest is a peculiar place. Hot spots usually sit way out on their own in the middle of a tectonic plate (think Hawaii or the Galapagos). Not Yellowstone -- it pokes its way to the surface just a few hundred miles from the edge of the North America plate, where a giant trench sends the Juan de Fuca tectonic plate sliding underneath Washington, Oregon, and northern California.

Peering into the middle of this tectonic traffic jam is a tricky business. So scientists, led by Mathias Obrebski of the University of California, Berkeley, had to build an image from seismic waves bouncing around inside the mantle. What they found was a subterranean world filled with violence.

The original data figures are a little hard to look at, but the team built a cartoon representation of what they think is going on down there. Around 19 million years ago, the Yellowstone hot spot first ascended from deep within the mantle. As it neared the surface, it ran into the subducting Juan de Fuca plate.

But the Juan de Fuca plate was itself young at the time (there's a mid-ocean ridge just off the coast of Oregon that forms brand new crust to this day), so it hadn't had the chance fully harden yet. When the crust and hot spot met, the hot mantle plume to found a weakness in the plate -- perhaps a pre-existing fracture -- and punched a giant hole through it.

So, who cares? The encounter has had several amazing consequences. First, and most obvious, it resurfaced much of northern Nevada, Idaho, and Wyoming over the last several million years in basalt through a series of massive volcanic eruptions. Then there were the tremendous supervolcanic explosions, which coated much of the western U.S. in thick blankets of ash and made the Yellowstone park region what it is today.

Second, the team points out that the rise of the Yellowstone plume also coincided with a large change in the rate at which the crust of the Pacific Ocean dives beneath North America. It's possible that the shattered underlying plate simply didn't pull as much weight anymore, and the subduction zone slowed down.

It's a new chapter in what we know about Yellowstone's legendary power to change the landscape. Not only did its massive eruptions coat North America in ash from Idaho to the Mississippi River, and south almost to the Gulf of Mexico, but its deep plume sent a ripple effect through the very roots of the continent and the Pacific Ocean that fundamentally altered the coastline of the Pacific Northwest.

Images: AGU