Ocean Trench

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R E S O U R C E L I B R A R Y

E N C Y C L O P E D I C E N T RY

Ocean trench

Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth.

G R A D E S

5 - 12+

S U B J E C T S

Earth Science, Geology, Geography, Physical Geography

C O N T E N T S

11 Images, 1 Video, 2 Links For the complete encyclopedic entry with media resources, visit: http://www.nationalgeographic.org/encyclopedia/ocean-trench/ Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth. Ocean trenches are found in every ocean basin on the planet, although the deepest ocean trenches ring the Pacific as part of the so-called “Ring of Fire” that also includes active volcanoes and earthquake zones.

Ocean trenches are a result of tectonic activity, which describes the movement of the Earth’s lithosphere. In particular, ocean trenches are a feature of convergent plate boundaries, where two or more tectonic plates meet. At many convergent plate boundaries, dense lithosphere melts or slides beneath less-dense lithosphere in a process called subduction, creating a trench.

Ocean trenches occupy the deepest layer of the ocean, the hadalpelagic zone. The intense pressure, lack of sunlight, and frigid temperatures of the hadalpelagic zone make ocean trenches some of the most unique habitats on Earth.

How Ocean Trenches Form

Subduction Zones

When the leading edge of a dense tectonic plate meets the leading edge of a less-dense plate, the denser plate bends downward. This place where the denser plate subducts is called a subduction zone.

Oceanic subduction zones almost always feature a small hill preceding the ocean trench itself. This hill, called the outer trench swell, marks the region where the subducting plate begins to buckle and fall beneath the more buoyant plate.

Some ocean trenches are formed by subduction between a plate carrying continental crust and a plate carrying oceanic crust. Continental crust is always much more buoyant than oceanic crust, and oceanic crust will always subduct.

Ocean trenches formed by this continental-oceanic boundary are asymmetrical. On a trench’s outer slope (the oceanic side), the slope is gentle as the plate gradually bends into the trench. On the inner slope (continental side), the trench walls are much more steep. The types of rocks found in these ocean trenches are also asymmetrical. The oceanic side is dominated by thick sedimentary rocks, while the continental side generally has a more igneous and metamorphic composition.

Some of the most familiar ocean trenches are the result of this type of convergent plate boundary. The Peru-Chile Trench off the west coast of South America is formed by the oceanic crust of the Nazca plate subducting beneath the continental crust of the South American plate. The Ryukyu Trench, stretching out from southern Japan, is formed as the oceanic crust of the Philippine plate subducts beneath the continental crust of the Eurasian plate.

More rarely, ocean trenches can be formed when two plates carrying oceanic crust meet. The Mariana Trench, in the South Pacific Ocean, is formed as the mighty Pacific plate subducts beneath the smaller, less-dense Philippine plate.

In a subduction zone, some of the molten material—the former seafloor—can rise through volcanoes located near the trench. The volcanoes often build volcanic arcs—island mountain ranges that lie parallel to the trench. The Aleutian Trench is formed where the Pacific plate subducts beneath the North American plate in the Arctic region between the U.S. state of Alaska and the Russian region of Siberia. The Aleutian Islands form a volcanic arc that swings out from the Alaskan Peninsula and just north of the Aleutian Trench.

Not all ocean trenches are in the Pacific, of course. The Puerto Rico Trench is a tectonically complex depression in part formed by the Lesser Antilles subduction zone. Here, the oceanic crust of the enormous North American plate (carrying the western Atlantic Ocean) is being subducted beneath the oceanic crust of the smaller Caribbean plate.

Accretionary Wedges

Accretionary wedges form at the bottom of ocean trenches created at some convergent plate boundaries. The rocks of an accretionary wedge are so deformed and fragmented they are known as melange—French for “mixture.”

Accretionary wedges form as sediments from the dense, subducting tectonic plate are scraped off onto the less-dense plate. Sediments often found in accretionary wedges include basalts from the deep oceanic lithosphere, sedimentary rocks from the seafloor, and even traces of continental crust drawn into the wedge. The most common type of continental crust found in accretionary wedges is volcanic material from islands on the overriding plate.

Accretionary wedges are roughly shaped like a triangle with one angle pointing downward toward the trench. Because sediments are mostly scraped off from the subducting plate as it falls into the mantle, the youngest sediments are at the bottom of this triangle and the oldest are at the more flattened area above. This is the opposite of most rock formations, where geologists must dig deep to find older rocks.

Active accretionary wedges, such as those located near the mouths of rivers or glaciers, can actually fill the ocean trench on which they form. (Rivers and glaciers transport and deposit tons of sediment into the ocean.) This accreted material can not only fill trenches, but rise above sea level to create islands that “hide” the ocean trenches beneath. The Caribbean island of Barbados, for example, sits atop the ocean trench created as the South American plate subducts beneath the Caribbean plate.

Life in the Trenches

Ocean trenches are some of the most hostile habitats on Earth. Pressure is more than 1,000 times that on the surface, and the water temperature is just above freezing. Perhaps most importantly, no sunlight penetrates the deepest ocean trenches, making photosynthesis impossible.

Organisms that live in ocean trenches have evolved with unusual adaptations to thrive in these cold, dark canyons. Their behavior is a test of the so-called “visual interaction hypothesis,” which states that the greater an organism’s visibility, the more energy it must expend to catch prey or repel predators. In general, life in dark ocean trenches is isolated and slow-moving.

Pressure

Pressure at the bottom of the Challenger Deep, the deepest spot on Earth, is about 12,400 tons per square meter (8 tons per square inch). Large ocean animals, such as sharks and whales, cannot live at this crushing depth.

Many organisms that thrive in these high-pressure environments lack gas-filled organs, such as lungs. These organisms, many related to sea stars or jellies, are made mostly of water and gelatinous material that cannot be crushed as easily as lungs or bones. Many of these creatures navigate the depths well enough to even make a vertical migration of more than 1,000 meters (3,281 feet) from the bottom of the trench—every day.

Even the fish in deep trenches are gelatinous. Several species of bulb-headed snailfish, for example, dwell at the bottom of the Mariana Trench. The bodies of these fishes have been compared to tissue paper.

Dark and Deep

Shallower ocean trenches have less pressure, but may still fall outside the photic or sunlight zone, where light penetrates the water.

Many fish species have adapted to life in these dark ocean trenches. Some use bioluminescence, meaning they produce their own “living light” in order to attract prey, find a mate, or repel a predator. Anglerfish, for instance, use a bioluminescent growth on the top of their heads (called an esca) to lure prey. The anglerfish then snaps up the little fish with its huge, toothy jaws.

Food Webs

Without photosynthesis, marine communities rely primarily on two unusual sources for nutrients. The first is “marine snow.” Marine snow is the continual fall of organic material from higher in the water column. Marine snow is mostly detritus, including excrement and the remains of dead organisms such as seaweed or fish. This nutrient-rich marine snow feeds such animals as sea cucumbers and vampire squid.

Another source of nutrients for ocean-trench food webs comes not from photosynthesis, but from chemosynthesis. Chemosynthesis is the process in which producers in the ocean trench, such as bacteria, convert chemical compounds into organic nutrients. The chemical compounds used in chemosynthesis are methane or carbon dioxide ejected from hydrothermal vents and cold seeps, which spew these toxic, hot gases and fluids into the frigid ocean water. One common animal that relies on chemosynthetic bacteria for food is the giant tube worm.

Exploring Trenches

Ocean trenches remain one of the most elusive and little-known marine habitats. Until the 1950s, many oceanographers thought that these trenches were unchanging environments nearly devoid of life. Even today, most research on ocean trenches has relied on seafloor samples and photographic expeditions.

That is slowly changing as explorers delve into the deep—literally. The Challenger Deep, at the bottom of the Mariana Trench, lies deep in the Pacific Ocean near the island of Guam. Only three people have visited the Challenger Deep, the deepest ocean trench in the world: a joint French-American crew (Jacques Piccard and Don Walsh) in 1960 and National Geographic Explorer-in-Residence James Cameron in 2012. (Two other unmanned expeditions have also explored the Challenger Deep.)

Engineering submersibles to explore ocean trenches is presents a huge set of unique challenges. Submersibles must be incredibly strong and resilient to contend with strong ocean currents, no visibility, and intense pressure of the Mariana Trench. Engineering a submersible to safely transport people, as well as delicate equipment, is even more challenging. The sub that took Piccard and Walsh to the Challenger Deep, the remarkable Trieste, was an unusual vessel called a bathyscaphe.

The Deepsea Challenger, Cameron’s submersible, successfully addressed engineering challenges in innovative ways. To combat deep-sea currents, the sub was designed to spin slowly as it descended. Lights on the sub were not incandescent or fluorescent bulbs, but arrays of tiny LEDs that illuminated an area of about 30 meters (100 feet). To adapt to the pressure of the deep, the sub was shaped like a sphere—the walls of a square or cylindershaped vessel would need to be at least three times thicker to avoid being crushed. The sub’s fuel was augmented by seawater to prevent the oil from compressing. Perhaps most startlingly, the Deepsea Challenger itself was designed to compress. Cameron and his team created glass-based syntactic foam that allowed the vehicle to compress under the ocean’s pressure—the Deepsea Challenger came back to the surface 7.6 centimeters (3 inches) smaller than when it descended.

Vocabulary

Part of
Term

accrete

Definition

to build up or grow together.

Speech

verb

mass of sediments scraped off from oceanic crust during subduction and piled up at the edge of the overriding plate. Also called an accretionary prism.

accretionary wedge

noun

volcano that has had a recorded eruption since the last glacial period, about 10,000 years ago.

active volcano noun

a modification of an organism or its parts that makes it more fit for existence. An adaptation is passed from generation to generation. region at Earth's extreme north, encompassed by the Arctic Circle.

adaptation

noun noun

Arctic asymmetric augment

adjective not identical on both sides.

verb

to enlarge or add to.

plural noun noun noun

(singular: bacterium) single-celled organisms found in every ecosystem on Earth.

bacteria basalt basin

type of dark volcanic rock. a dip or depression in the surface of the land or ocean floor. vehicle used to explore the deep ocean. Developed after the bathysphere.

bathyscaphe

noun

light emitted by living things through chemical reactions in their bodies.

bioluminescencenoun

adjective,

bone

structure composing the skeleton of vertebrate animals.

noun verb

buckle

to bend, fold, or fall apart quickly.

buoyant canyon

adjective capable of floating. noun deep, narrow valley with steep sides.

Part of Speech

  • Term
  • Definition

greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.

carbon dioxide noun chasm

noun

a deep opening in the earth's surface. process by which some microbes turn carbon dioxide and water into carbohydrates using energy obtained from inorganic chemical reactions.

chemosynthesis noun coast

noun noun

edge of land along the sea or other large body of water. marine environment where hydrogen sulfide and methane seep up from beneath the seafloor and mix with the ocean water. substance having at least two chemical elements held together with chemical bonds.

cold seep compound

noun

compress contend continental crust

verb verb

to press together in a smaller space. to sincerely assert.

noun noun

thick layer of Earth that sits beneath continents.

convergent plate boundary current

area where two or more tectonic plates bump into each other. Also called a collision zone.

noun noun verb

steady, predictable flow of fluid within a larger body of that fluid. tube or long, circular object.

cylinder deform

to put out of shape or distort.

delicate delve

adjective fragile or easily damaged.

verb

to research or investigate thoroughly.

dense

adjective having parts or molecules that are packed closely together.

depression descend detritus devoid

noun verb noun

indentation or dip in the landscape. to go from a higher to a lower place. non-living organic material, often decomposing. adjective lacking or not having something.

dominate

verb noun verb

to overpower or control. the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity. to get rid of or throw out.

earthquake eject elusive

adjective difficult to capture. the art and science of building, maintaining, moving, and demolishing structures.

engineering

noun

Part of

  • Term
  • Definition

Speech

enormous equipment esca

adjective very large.

noun noun

tools and materials to perform a task or function. long, thin, fleshy growth from the head of an anglerfish. to develop new characteristics based on adaptation and natural selection.

evolve

verb

excrement expedition

noun noun

waste material discharged from the body. journey with a specific purpose, such as exploration. pre-eminent explorers and scientists collaborating with the National Geographic Society to make groundbreaking discoveries that generate critical scientific information, conservation-related initiatives and compelling stories.

Explorer-inResidence

noun

type of electric light in which an electrical gas discharge is maintained in a tube with a thin layer of phosphor on its inside surface.

fluorescent

noun

food web fragment frigid

noun noun

all related food chains in an ecosystem. Also called a food cycle. piece or part. adjective very cold.

fuel

noun

material that provides power or energy. state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

gas

noun

gelatinous geologist glacier

adjective resembling or behaving like a jelly, gel, or gelatin.

noun noun

person who studies the physical formations of the Earth. mass of ice that moves slowly over land. environment where an organism lives throughout the year or for shorter periods of time.

habitat

noun noun noun

hadalpelagic zone

deepest zone of the open ocean, starting at around 6,000 meters (20,000 feet). land that rises above its surroundings and has a rounded summit, usually less than 300 meters (1,000 feet).

hill hostile

adjective confrontational or unfriendly.

hydrothermal vent

noun

opening on the seafloor that emits hot, mineral-rich solutions.

igneous rock illuminate

noun verb

rock formed by the cooling of magma or lava. to shine light on.

Part of Speech

  • Term
  • Definition

a type of electric light in which light is produced by a filament heated by electric current.

incandescent

adjective

inner slope innovative

noun

landward or continental side of an ocean trench. adjective new, advanced, or original.
(light emitting diode) device (semiconductor) that emits light when

LED

noun

an electric current passes through it.

lithosphere lung

noun noun noun noun

outer, solid portion of the Earth. Also called the geosphere. organ in an animal that is necessary for breathing. object used to attract an animal or other organism. middle layer of the Earth, made of mostly solid rock.

lure mantle marine

adjective having to do with the ocean. continuous fall of organic and inorganic particles (including the

marine snow

noun

remains of marine organisms, fecal matter, shells, and sand) from the upper layers of the water column to the seafloor. one of a breeding pair of animals.

mate

noun noun

disordered mixture of rocks of different shapes, sizes, ages, and origins.

melange metamorphic rock

rock that has transformed its chemical qualities from igneous or sedimentary.

noun noun noun

methane

chemical compound that is the basic ingredient of natural gas. movement of a group of people or animals from one place to another.

migration molten

adjective solid material turned to liquid by heat.

mountain range noun

series or chain of mountains that are close together. place where a river empties its water. Usually rivers enter another body of water at their mouths.

mouth

noun

navigate

verb noun noun

to plan and direct the course of a journey.

nutrient

substance an organism needs for energy, growth, and life. thin layer of the Earth that sits beneath ocean basins. person who studies the ocean.

oceanic crust oceanographer noun ocean trench ocean trench

noun noun

a long, deep depression in the ocean floor. a long, deep depression in the ocean floor. fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.

oil

noun noun

organ

group of tissues that perform a specialized task.

Part of Speech
Term

organic

Definition

adjective composed of living or once-living material.

outer slope outer trench swell

noun

oceanic side of an ocean trench. hill on the seafloor near an ocean ridge, where the oceanic lithosphere begins to subduct beneath the overriding plate.

noun

parallel

adjective equal distance apart, and never meeting.

penetrate peninsula

verb

to push through.

noun

piece of land jutting into a body of water. process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars. animal that hunts other animals for food. force pressed on an object by another object or condition, such as gravity.

photosynthesis noun predator pressure prey

noun noun noun noun verb

animal that is hunted and eaten by other animals. organism on the food chain that can produce its own energy and nutrients. Also called an autotroph.

producer rely

to depend on.

remarkable repel

adjective unusual and dramatic. verb to resist or push back. adjective able to recover.

resilient

horseshoe-shaped string of volcanoes and earthquake sites around

Ring of Fire

noun

edges of the Pacific Ocean.

river

noun noun noun

large stream of flowing fresh water.

rock

natural substance composed of solid mineral matter. surface layer of the bottom of the ocean. base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle. marine algae. Seaweed can be composed of brown, green, or red algae, as well as "blue-green algae," which is actually bacteria. solid material transported and deposited by water, ice, and wind. rock formed from fragments of other rocks or the remains of plants or animals.

seafloor sea level

seaweed

noun noun noun noun

sediment sedimentary rock

region of land stretching across Russia from the Ural Mountains to the Pacific Ocean.

Siberia

noun

spew

verb

to eject or discharge violently.

sphere

noun

round object.

Part of
Term

startling

Definition
Speech

adjective surprising or astonishing. adjective extreme incline or decline.

steep

process of one tectonic plate melting, sliding, or falling beneath another.

subduction submersible

noun noun

small submarine used for research and exploration. The upper zone of the ocean. This zone goes down to about 200 meters (660 feet). Also called the photic, euphotic, or epipelagic zone.

sunlight zone noun

material consisting of tiny hollow "microballoons" made from material such as glass or carbon.

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  • Mantle Flow Through the Northern Cordilleran Slab Window Revealed by Volcanic Geochemistry

    Mantle Flow Through the Northern Cordilleran Slab Window Revealed by Volcanic Geochemistry

    Downloaded from geology.gsapubs.org on February 23, 2011 Mantle fl ow through the Northern Cordilleran slab window revealed by volcanic geochemistry Derek J. Thorkelson*, Julianne K. Madsen, and Christa L. Sluggett Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada ABSTRACT 180°W 135°W 90°W 45°W 0° The Northern Cordilleran slab window formed beneath west- ern Canada concurrently with the opening of the Californian slab N 60°N window beneath the southwestern United States, beginning in Late North Oligocene–Miocene time. A database of 3530 analyses from Miocene– American Holocene volcanoes along a 3500-km-long transect, from the north- Juan Vancouver Northern de ern Cascade Arc to the Aleutian Arc, was used to investigate mantle Cordilleran Fuca conditions in the Northern Cordilleran slab window. Using geochemi- Caribbean 30°N Californian Mexico Eurasian cal ratios sensitive to tectonic affi nity, such as Nb/Zr, we show that City and typical volcanic arc compositions in the Cascade and Aleutian sys- Central African American Cocos tems (derived from subduction-hydrated mantle) are separated by an Pacific 0° extensive volcanic fi eld with intraplate compositions (derived from La Paz relatively anhydrous mantle). This chemically defi ned region of intra- South Nazca American plate volcanism is spatially coincident with a geophysical model of 30°S the Northern Cordilleran slab window. We suggest that opening of Santiago the slab window triggered upwelling of anhydrous mantle and dis- Patagonian placement of the hydrous mantle wedge, which had developed during extensive early Cenozoic arc and backarc volcanism in western Can- Scotia Antarctic Antarctic 60°S ada.
  • Constraints on the Moho in Japan and Kamchatka

    Constraints on the Moho in Japan and Kamchatka

    Tectonophysics 609 (2013) 184–201 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Review Article Constraints on the Moho in Japan and Kamchatka Takaya Iwasaki a, Vadim Levin b,⁎, Alex Nikulin b, Takashi Iidaka a a Earthquake Research Institute, University of Tokyo, Japan b Rutgers University, NJ, USA article info abstract Article history: This review collects and systematizes in one place a variety of results which offer constraints on the depth Received 1 July 2012 and the nature of the Moho beneath the Kamchatka peninsula and the islands of Japan. We also include stud- Received in revised form 12 November 2012 ies of the Izu–Bonin volcanic arc. All results have already been published separately in a variety of venues, and Accepted 22 November 2012 the primary goal of the present review is to describe them in the same language and in comparable terms. Available online 3 December 2012 For both regions we include studies using artificial and natural seismic sources, such as refraction and reflec- tion profiling, detection and interpretation of converted-mode body waves (receiver functions), surface wave Keywords: Kamchatka dispersion studies (in Kamchatka) and tomographic imaging (in Japan). The amount of work done in Japan is Japan significantly larger than in Kamchatka, and resulting constraints on the properties of the crust and the upper- Crustal structure most mantle are more detailed. Upper-mantle structure Japan and Kamchatka display a number of similarities in their crustal structure, most notably the average Moho crustal thickness in excess of 30 km (typical of continental regions), and the generally gradational nature of the crust–mantle transition where volcanic arcs are presently active.
  • Geometrical Effects of a Subducted Seamount on Stopping Megathrust

    Geometrical Effects of a Subducted Seamount on Stopping Megathrust

    GEOPHYSICAL RESEARCH LETTERS, VOL. 40, 1–6, doi:10.1002/grl.50509, 2013 Geometrical effects of a subducted seamount on stopping megathrust ruptures Hongfeng Yang,1,2 Yajing Liu,1,3 and Jian Lin1 Received 6 March 2013; revised 18 April 2013; accepted 25 April 2013. [1] We have numerically simulated dynamic ruptures along rich sediments into seismogenic zone [Bangs et al., 2006]. a “slip-weakening” megathrust fault with a subducted The presence of entrained fluid-rich sediments in the vicinity seamount of realistic geometry, demonstrating that of a subducted seamount would reduce effective normal seamounts can act as a barrier to earthquake ruptures. Such stress and lubricate the thrust interface, leading to little barrier effect is calculated to be stronger for increased elastic strain accumulation and thus inhibiting coseismic seamount normal stress relative to the ambient level, for ruptures [Mochizuki et al., 2008; Singh et al., 2011]. Further- larger seamount height-to-width ratio, and for shorter more, it was proposed that seamount subduction may create seamount-to-nucleation distance. As the seamount height a complex fracture network in the overriding plate, making it increases from 0 to 40% of its basal width, the required unfavorable for the generation of large earthquakes [Wang increase in the effective normal stress on the seamount to and Bilek, 2011]. Thus, the specific mechanisms for stop ruptures drops by as much as ~20%. We further subducted seamounts to stop coseismic ruptures could be demonstrate that when a seamount is subducted adjacent to complex and remain open for debate. the earthquake nucleation zone, coseismic ruptures can be [3] Previous numerical studies have modeled a subducted stopped even if the seamount has a lower effective normal seamount as a patch under elevated effective normal stress stress than the ambient level.
  • Subducting Oceanic High Causes Compressional Faulting In

    Subducting Oceanic High Causes Compressional Faulting In

    Available online at www.sciencedirect.com Tectonophysics 466 (2009) 255–267 www.elsevier.com/locate/tecto Subducting oceanic high causes compressional faulting in southernmost Ryukyu forearc as revealed by hypocentral determinations of earthquakes and reflection/refraction seismic data ⁎ Yvonne Font a, , Serge Lallemand b a Géosciences Azur, UMR IRD–CNRS–UPMC–UNSA 6526, 06235 Villefranche-sur-Mer, France b Géosciences Montpellier, UMR CNRS–UM2 5243, CC.60, UM2, place E. Bataillon, 34095 Montpellier, France Available online 22 November 2007 Abstract Absolute earthquake hypocenter locations have been determined in the area offshore eastern Taiwan, at the Southernmost Ryukyu subduction zone. Location process is run within a 3D velocity model by combining the Taiwanese and neighboring Japanese networks and using the 3D MAXI technique. The study focuses on the most active seismic cluster in the Taiwan region that occurs in the forearc domain offshore eastern Taiwan. Earthquakes distribute mainly along 2 active planes. The first one aligns along the subduction interface and the second one, shallower affects the overriding margin. Focal mechanisms within the shallow group indicate that nodal planes are either compatible with high-angle back- thrusts or low-angle thrusts. The active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench-perpendicular strong compression. By integrating the seismological image into the regional context, we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en-échelon high-angle reverse faults accommodating the uplift of a broken piece of Ryukyu Arc basement, called Hoping Basement Rise. The uplift is inferred to be caused by the subduction of an oceanic relief, either exotic block, seamount or oceanic crust sliver.
  • The Next Generation of Ocean Exploration. Kelly Walsh Repeats Father’S Historic Dive, 60 Years Later, on Father’S Day Weekend

    The Next Generation of Ocean Exploration. Kelly Walsh Repeats Father’S Historic Dive, 60 Years Later, on Father’S Day Weekend

    From father to son; the next generation of ocean exploration. Kelly Walsh repeats father’s historic dive, 60 years later, on Father’s Day weekend DSSV Pressure Drop. Challenger Deep, Mariana Trench 200miles SW of Guam. June 20th, 2020 – Kelly Walsh, 52, today completed a historic dive to approximately 10,925m in the Challenger Deep. The dive location was the Western Pool, the same area that was visited by Kelly’s father, Captain Don Walsh, USN (Ret), PhD, who was the pilot of the bathyscaph ‘Trieste’ during the first dive to the Challenger Deep in 1960. Mr. Walsh’s 12- hour dive, coordinated by EYOS Expeditions, was undertaken aboard the deep-sea vehicle Triton 36000/2 ‘Limiting Factor” piloted by the owner of the vehicle Victor Vescovo, a Dallas, Texas based businessman and explorer. The expedition to the Challenger Deep is a joint venture by Caladan Oceanic, Triton Submarines and EYOS Expeditions. Mr. Vescovo and his team made headlines last year by completing a circumnavigation of the globe that enabled Mr. Vescovo to become the first person to dive to the deepest point of each of the worlds five oceans. The dives by father and son connect a circle of exploration history that spans 60 years. “It was a hugely emotional journey for me,” said Kelly Walsh aboard DSSV Pressure Drop, the expedition’s mothership. “I have been immersed in the story of Dad’s dive since I was born-- people find it fascinating. It has taken 60 years but thanks to EYOS Expeditions and Victor Vescovo we have now taken this quantum leap forward in our ability to explore the deep ocean.
  • Latitude Volcanoes Dubious Case for Slab Melting in the Northern

    Latitude Volcanoes Dubious Case for Slab Melting in the Northern

    Dubious case for slab melting in the Northern volcanic zone of the Andes: Comment and Reply COMMENT Moreover, the SiO2 range of “putative slab melts” is assumed to represent the silica content of primary magmas produced in front of the E. Bourdon Carnegie Ridge. Such an assumption should be valid only if all magmas Department of Geology, Royal Holloway, University of London, represent true primary melts. However, fractional crystallization is an effi - Egham, Surrey TW20 0EX, UK cient process able to strongly modify silica content of magmas (including P. Samaniego in the Northern volcanic zone). Consequently, silica defi nitely appears to Departamento de Geofísica, Escuela Politecnica Nacional, be an inappropriate geochemical feature to distinguish slab melts. AP 17-01-2759, Quito, Ecuador Garrison and Davidson (2003) also argue that the lack of unequivocal M. Monzier, C. Robin, J.-P. Eissen geochemical variation along the arc excludes slab melting. However, data re- IRD, UR 031, Laboratoire Magmas et Volcans, Universite Blaise cently presented (Monzier et al., 2003) show systematic geochemical varia- Pascal, 5 rue Kessler, 63038 Clermont-Ferrand, France tion along the arc, all showing a negative or positive peak between 0.5°N and H. Martin 1°S. Among those, Y and La/Yb display clear minimums and maximums, UMR 6524, Laboratoire Magmas et Volcans, Universite Blaise Pascal, respectively, precisely where the Carnegie Ridge is subducting (Fig. 1). Such 5 rue Kessler, 63038 Clermont-Ferrand, France behavior refl ects the intervention of slab melts in the petrogenesis of the magmas, directly related to the subduction of the Carnegie Ridge. Recently, Garrison and Davidson (2003) questioned the possibility We agree with the Garrison and Davidson (2003) conclusion that that the adakites of the Northern volcanic zone of the Andes were gener- the magma geochemical signature characterizes the source and not any ated by slab melting.