Mariana Trench

 Beneath our feet, beneath our towns, beneath our countries and beneath our oceans is the outer covering of our planet’s core, the Earth’s crust.

Because of intense pressure even farther below, our crust has broken up into eight large tectonic plates (and a host of smaller plates). The plates collide with each other, with the larger plate tending to thrust underneath the smaller plate. The collision of tectonic plates causes earthquakes, volcanoes, and oceanic trenches around the world.

A very long time ago the Pacific plate (the largest plate) collided with the Mariana Plate and plowed underneath it into the earth’s mantle. The trough created by this motion became known as the Mariana Trench.

Cross section

Water trapped between the two plates heated and then exploded up through the overlaying Mariana Plate, creating a curved chain of volcanic islands (to the north) and habitable islands (to the south) which includes Guam. The Trench itself is 1,500 miles long and 43 miles wide: a curved, deep scar located east of the Philippine Islands, and 3,500 miles southwest of Hawaii, in a part of the world known as Micronesia. 


The islands were discovered before the Trench. In 1521 Spanish explorer Ferdinand Magellan landed on one of the southern islands, which was inhabited by the Chamorro people (ethnically similar to Filipinos), who excelled in seafaring, weaving, and pottery making. 

The encounter was not a happy one. Magellan accused the Chamorro of stealing his supplies, provisions, and everything else that wasn’t nailed down. In return the Spanish burned down huts and killed the men, until their items were restored. Still upset sailing away, Magellan named the island Islas de los Ladrones (Islands of the Thieves). 

The Spanish visited again in 1668. These Spaniards were Jesuits, and they renamed the island chain the Mariana Islands, after Spain’s reigning queen and regent. Colonizing and Catholicizing the islands required military support, although the introduction of European diseases subdued the Chamorro more than military force. Within a century interbreeding with the Spanish caused the Chamorro to cease to exist as a separate people.

In 1898 the United States defeated Spain in the Spanish-American War, and took possession of the Mariana Islands, including the southern island of Guam. The Mariana Trench was discovered, and explored by the British ship HMS Challenger. Using the equipment of the time, the British estimated the depth of the Trench to be approximately five miles, and located the deepest spot in the trench, which they named Challenger Deep.

Scientists could only speculate as to how deep the Trench really was, and whether life could survive that deep in the ocean. It was not until 1960 that human beings visited Challenger Deep and came back to talk about it.

Bathyscaphe, 1960

Jacques Piccard was a Swiss engineer. He and his father designed a sort of submarine they called a “bathyscaphe.” In 1958 the U.S. Navy purchased the vehicle and asked for pilots to learn to operate it. Only two submariners were interested. One of them, Don Walsh, got the job. “I just thought it would be fun,” he said later.

Walsh and Piccard, 1960

On January 20 1960, Walsh and Piccard got into the bathyscaphe, named Trieste, and took a five hour dive almost seven miles straight down to the bottom of Challenger Deep, the deepest spot of the Trench. They spent twenty minutes there. Although Trieste stirred up enough sand and silt to make it hard to see anything, Walsh and Piccard did see an unusual creature:

“... as we were settling this final fathom, I saw a wonderful thing. Lying on the bottom just beneath us was some type of flatfish, resembling a sole, about 1 foot long and 6 inches across. Even as I saw him, his two round eyes on top of his head spied us — a monster of steel — invading his silent realm…Here, in an instant, was the answer that biologists had asked for the decades. Could life exist in the greatest depths of the ocean? It could!”

This news surprised many scientists, since the Mariana Trench is over a mile lower than Mount Everest is high, meaning that if Everest was dropped into the Trench its peak would be one mile below the ocean’s surface.

At these freakish depths everything is very dark. And really cold: the water temperature is slightly above freezing. The water pressure in Challenger Deep is eight tons per square inch, about one thousand times the pressure at sea level.

The Trench is not just dark. It is very old. The international scientific community considers it the oldest place on the floor of any ocean on earth. Crustal material at the western edge of the Pacific Plate is some of the oldest oceanic crust on earth. Some estimates date it at up to 170 million years old.

In 1995 a Japanese deep sea probe called Kaiko visited Challenger Deep and collected samples of the silt that Trieste stirred up thirty five years before. The official scientific term for this substance is “ooze:” that is, marine organisms and sediment made up of shells and other parts of microscopic animal and plant plankton.

In 2009 America sent its own unmanned probe, the Nereus, to Challenger Deep for a ten hour expedition collecting soil samples and other data, including live video feeds. That same year President George W. Bush established most of the Mariana trench as a wildlife reserve, a protected zone requiring government approval for any research carried out in the area.

The most celebrated recent exploration was in 2012 by filmmaker James Cameron. Funded by National Geographic, Cameron became the first human to reach Challenger Deep solo. His descent in a “vertical torpedo” took 2 ½ hours, and his ascent a speedy seventy minutes. The fifty seven year old Cameron was on the bottom for three hours, collecting samples and 3-D video illumined by an eight foot tower of LED lights lending a ghostly beauty to the lowest place we know of.

James Cameron, 2012

Cameron intended a much longer stay down low, but malfunctions caused him to cut the trip short, and prevented him from collecting all the samples he wanted to. However, in December 2014, the University of Aberdeen released a video of life in the Mariana Trench taken during a recent exploration by the UK’s Hadal-Lander, a deep sea diving vehicle that captured proof there are fish at the deepest point of the ocean.

"Snailfish" in Mariana Trench

There is a type of snailfish: a gossamer, almost translucent creature with an overly large head and fragile, winglike fins. Given the intense water pressure, it is difficult to believe something that wispy would not be crushed to death. This particular fish has never been seen before. 

Great big crusty thing at bottom of ocean

There was also a new, large crustacean creature. Scientists call it a supergiant amphipod. Future dives promise more and better glimpses of life at the bottom of the world. 

There may come a day when the Mariana Trench becomes as heavily trafficked as Mount Everest. The Trench may also become a nuclear waste dump. The thought is that the movement of the tectonic plates might push the waste further and further into the earth’s mantle, that is, further away from us. It is unclear at present whether this is a really good idea, or a really bad idea. For one thing, plate thrusting can cause massive earthquakes. Does the combination of massive earthquakes and nuclear waste make anyone else feel queasy? 

The point for now is moot since international law prohibits dumping nuclear waste in the ocean. But keep your eye on the Mariana Trench. It will continue to be in the news.