Seamount, large submarine volcanic mountain rising at least 1,000 m (3,300 feet) above the surrounding deep-sea floor; smaller submarine volcanoes are called sea knolls, and flat-topped seamounts are called guyots.

I would expect them to be islands. As a volcano grows older the magma it releases would accumulate and solidify until the volcano was no longer below the water level. The longer a volcano is active the less likely it is to remain underwater due to this gradual build up.

Seamounts are underwater mountains that rise hundreds or thousands of feet from the seafloor. They are generally extinct volcanoes that, while active, created piles of lava that sometimes break the ocean surface.

A seamount is an underwater mountain formed by volcanic activity. Seamounts — undersea mountains formed by volcanic activity — were once thought to be little more than hazards to submarine navigation.

Seamounts are neither islands nor islets but mountains rising from the seafloor that do not reach the sea level. The difference between a seamount and an island is that an island has its peak above the surface of the water (sea level) while the peak of a seamount remains below the water surface.

A guyot, or seamount, is an undersea mountain. Seamounts are formed by volcanic activity and can be taller than 10,000 feet . They can be isolated or part of large mountain chains. The New England Seamount contains more than 30 peaks that stretch 994 miles from the coast of New England.

Guyots show evidence of having once been above the surface, with gradual subsidence through stages from fringed reefed mountain, coral atoll, and finally a flat-topped submerged mountain.

How are Guyots Formed? Volcanic activity forms a guyot under the ocean. Vents in the seafloor over an area of volcanic activity may produce lava periodically to grow a guyot or other seamount formation.

These data indicate that guyots originate as volcanic islands at the shallow crests of mid-oceanic ridges and rises. During and immediately after their formation, the islands are truncated by wave erosion. Guyots of the western Pacific Ocean are capped by drowned coral atolls and coral reefs.

The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface.

This thick covering hosts a different suite of animals than are found on the steeper, hard flanks of the guyot: sediment-dwelling shrimps, isopods, crabs, sea stars, brittle stars, sea cucumbers, sea pens, worms of various kinds, and even a few species of sponges.

Arnold Henry Guyot

The largest three guyots are all in the North Pacific: the Kuko Guyot (estimated 24,600 km2), Suiko Guyot (estimated 20,220 km2) and the Pallada Guyot (estimated 13,680 km2).

A tuya is a flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. Discovering and dating the lava flows in a tuya has proven useful in reconstructing past glacial ice extents and thicknesses.

An ocean basin is formed when water has covered a large portion of the Earth’s crust. Over a long period of time, an oceanic basin can be created by the spreading of the seafloor and the movement of tectonic plates.

Pacific Ocean

Ocean basins are the regions that are below sea level. A seamount is a large submerged volcanic mountain rising from the ocean floor, and a guyot is a submerged volcanic mountain with a flat top. Oceanic trenches are depressions in the ocean floor. Oceanic trenches form when one plate subducts or slides under another.

• Mariana Trench. Located in the western Pacific Ocean, the Marina Trench is considered to be the deepest part of the Earth’s surface.
• Tonga Trench.
• Philippine Trench.
• Kuril- Kamchatka Trench.
• Kermadec Trench.
• Izu-Ogasawara Trench.
• Japan Trench.
• Puerto Rico Trench.

Mariana Trench

Deep-sea trenches generally lie seaward of and parallel to adjacent island arcs or mountain ranges of the continental margins. They are closely associated with and found in subduction zones—that is, locations where a lithospheric plate bearing oceanic crust slides down into the upper mantle under the force of gravity.

Despite its immense distance from everywhere else, life seems to be abundant in the Trench. Recent expeditions have found myriad creatures living out their lives at the bottom of the sea-floor. Xenophyophores, amphipods, and holothurians (not the names of alien species, I promise) all call the trench home.

Which best describes an ocean trench? A deep, curved depression near the margin of a continent or chain of volcanic islands. Lava erupts from the mid-ocean ridge and is carried away as the floor of the ocean spreads apart.

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