The Hawaiian Trough, otherwise known as the Hawaiian Deep, is a moat-like depression of the

seafloor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth an ...

surrounding the Hawaiian Islands. The weight from the volcanic island chain depresses the plastic lithosphere that is already weakened by the underlying thermal hotspot, causing subsidence to occur. The location with the greatest rate of subsidence is directly above the hotspot with a rate of about per year. The Hawaiian Trough is about deep and has a radius of about .Rees, B. A., Detrick, R. S., & Coakley, B. J. (1993). Seismic stratigraphy of the Hawaiian flexural moat. ''Geologic Society of America Bulletin'', ''105'', 189–205. The subsiding lithosphere is balanced out and through the concept of

isostasy Isostasy (Greek ''ísos'' "equal", ''stásis'' "standstill") or isostatic equilibrium is the state of gravitational equilibrium between Earth's crust (or lithosphere) and mantle such that the crust "floats" at an elevation that depends on its ...

a part of the crust surrounding the trough is levered upwards creating the Hawaiian Arch. The Hawaiian Arch extends about above the surrounding ocean floor, and contains tilted

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...

Trough Development

The Hawaiian Trough is filled with a stratified sedimentary section >2 km thick that was deposited in 4 sequential stages. The first (bottom) stage is a basal layer composed of 50 –100 m of primarily pelagic sediment. This layer was slowly deposited on the 80-Ma oceanic crust before the depression formed. The sediment in this layer is from a variety of different sources including wind blown material, slowly setting fine-grained sediment, and biogenic debris. The second stage is characterized by a bedded layer of volcanoclastic material that fills the Trough as it quickly subsides due to large influxes of material from nearby volcanos. The majority of material in this layer was transported by turbidity currents that flow along the axis of the moat and transport material from mass wasting events. During the third stage, the depression fills with slumps and debris avalanches which creates a layer of landslide debris. This layer contributes to the bulk of the sediment in the Trough. In the fourth and final stage, volcanic activity and subsistence effectively ends, and sediment deposits brought my turbidity currents, create a ponded unit in the deepest part of the Trough. This top layer is primary composed of turbidite and pelagic sediments. The largest

mass wasting Mass wasting, also known as mass movement, is a general term for the movement of rock or soil down slopes under the force of gravity. It differs from other processes of erosion in that the debris transported by mass wasting is not entrained in ...

events, such as the Nuuanu-Wailau debris avalanches and the Hana slump, overfilled the moat and created a series of sub-basins. These large deposits block the lateral transport of sediment along the Trough, especially in the deepest sections. Storm surges and

internal wave Internal waves are gravity waves that oscillate within a fluid medium, rather than on its surface. To exist, the fluid must be stratified: the density must change (continuously or discontinuously) with depth/height due to changes, for example, in ...

s trigger mass wasting events from older volcanos on the western side of the ridge, earthquakes provoke this behavior from younger volcanos on the eastern side^{/sup>.

Coral Reefs

The coral reefs in the Hawaiian Trough are described as mesophotic coral ecosystems, which can be found between 100 and 500 feet below sea level. 43 percent of fish

Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...
species documented at the mesophotic reefs are unique to the Hawaiian Islands. At Maui's ‘Au’au channel the largest uninterrupted mesophotic coral ecosystem was discovered, with an area larger than 3 square miles. These reefs contained many stony, reef building coral that belong to the genus Leptoseris, which are adapted for deep water environments. These coral environments are not greatly understood because the great depth where they exist make exploration difficult.

See also

* South Arch volcanic field
* Submarine landslide

Submarine landslides are marine landslides that transport sediment across the continental shelf and into the deep ocean. A submarine landslide is initiated when the downwards driving stress (gravity and other factors) exceeds the resisting str ...

Sources

External links

Overview of Hawaiian Arch geology (PDF)

New Evidence for Massive Landslides from the Hawaiian Islands (PDF)
{{Webarchive, url=https://web.archive.org/web/20040723052409/http://www.usssp-iodp.org/PDFs/Greatest_Hits/Rhythms/Garcia.pdf , date=2004-07-23

Geology of Hawaii
Oceanography
Marine geology}