Pacific Ocean

The Pacific is a very old ocean.

Around its edges, the ground often shakes and volcanoes erupt. People call this ring the Ring of Fire.

The Pacific is the oldest of today's ocean basins. Its oldest rocks are about 200 million years old.

Around the edges of the Pacific, plates of Earth's crust push together, and one plate slides down under another. Along this ring lie deep trenches, chains of islands and volcanic mountains. Because of all the earthquakes and volcanoes there, the edge of the Pacific is called the Ring of Fire.

NOAA's National Ocean Service calls the Pacific the oldest existing ocean basin, with its oldest rocks dated at about 200 million years. The "Ring of Fire" is a nearly continuous series of oceanic trenches, island arcs and volcanic mountain ranges, together with several plate boundaries, encircling the Pacific basin; its intense earthquake and volcanic activity occurs near subduction zones, where one plate is forced under another.

Its trenches include the deepest known places in the ocean. The Five Deeps Expedition measured Challenger Deep in the Mariana Trench at 10,924 ± 15 m, with a submersible reading of 10,925 ± 4 m, and confirmed Horizon Deep in the Tonga Trench as the Pacific's second-deepest point at 10,816 ± 16 m.

The deepest place in the ocean is in the Pacific.

It is called Challenger Deep. It is very dark and cold down there. Only special submarines can go that deep.

Challenger Deep, in the Mariana Trench, is the deepest place known in the ocean. In 2018–2019 the Five Deeps Expedition used sound waves to map the deepest point of every ocean, and a deep-diving submersible, the DSV Limiting Factor, dived to each one.

Even deep-sea fish don't go all the way down. The deepest fish ever filmed, a snailfish, was 8,336 meters down. NOAA says it is likely that no fish lives deeper than about 8,400 meters because of the extreme pressure, while Challenger Deep is about 11,000 meters deep.

The Five Deeps Expedition (2018–2019) mapped about 550,000 km² of seafloor with a full-ocean-depth multibeam echosounder, correcting the depths with CTD (conductivity, temperature and depth) data, and dived to each ocean's deepest point with the submersible DSV Limiting Factor; in the Mariana Trench it found 10,924 ± 15 m by sonar and 10,925 ± 4 m by submersible.

NOAA Ocean Exploration notes that the deepest confirmed fish, a snailfish filmed at 8,336 m, is about 1,000 m deeper than any other fish seen alive, and that research suggests a limit for fish between about 8,200 and 8,400 m set by pressure. Challenger Deep, at about 11,000 m, lies far below that limit.

Little fish called snailfish live in oceans all over the world.

Some live in shallow water. Some live very deep down in ocean trenches, where it is dark.

Snailfishes are fish shaped a little like tadpoles, with big heads, small eyes and no scales. They are found all around the world, from shallow coastal seas down to ocean trenches, and some kinds are especially well suited to deep water.

In 2023 NOAA filmed a snailfish off Alaska 1,365 meters down. The deepest snailfish ever seen, found by scientists the same year, was more than six times deeper, at 8,336 meters.

Snailfishes, tadpole-like fish with large heads, small eyes and no scales, range from shallow coastal seas to ocean trenches worldwide, and some species are especially well adapted to deep water. NOAA Ocean Exploration filmed one at 1,365 m on its 2023 Seascape Alaska 5 expedition; the deepest-living snailfish ever seen, reported by Jamieson and colleagues in 2023, was at 8,336 m, more than six times deeper.

In 1970 a deep-sea cusk eel was caught in a net that descended to 8,370 m, though it is unclear whether it was caught at the trawl's deepest point. Research suggests a boundary for fish between about 8,200 and 8,400 m; if so, the deepest parts of the Pacific's trenches, such as Challenger Deep, lie beyond the reach of fish.

The Pacific has many beaches.

If the ground shakes hard at the beach, go to high ground with a grown-up. Listen to the people in charge.

Because the Ring of Fire has many earthquakes, tsunamis can reach Pacific coasts. The US National Weather Service explains two kinds of warning: official warnings, and natural warnings that you notice yourself.

Natural warnings include a strong or long earthquake, the sea suddenly draining away like a very low tide, or a loud roar from the ocean. Then go as high or as far inland as you can, away from the water, and follow instructions from local officials.

The US National Weather Service describes two types of tsunami warning, official and natural, and says to respond to whichever comes first. Natural warnings in a hazard zone or low-lying coastal area are a strong or long earthquake, the ocean acting strangely (a fast-rising flood, a wall of water, or the sea draining away to show the floor like a very low tide) or a loud roar from the ocean; a tsunami could then arrive within minutes.

In an earthquake, drop, cover and hold on, then move quickly to a safe place outside the hazard zone, following evacuation signs or going as high or as far inland as possible. Flooding and strong currents can continue for hours or days, so always follow local officials' instructions.