What is a region in which the sea floor and its sediments melt?

Answer 1

The sea floor bends down as a continental plate moves in the direction of the sea floor.

Less dense continental materials float over the more basaltic sea floor and sediments - this buoyant force lets the plate rise above the seafloor and push the sea floor down into the crust, following the descending edge of a convection cell in the crust, The area where this happens is called a subduction zone.

For a huge example, look at the west coast of North and South America where the Pacific is dragged beneath the continents. The hot rock , like a hot air balloon, rises through the continental crust, pushing it up and making mountains at the edge of the crustal plate. The rock stays so hot that it sometimes is pushed out the top of a mountain where the gases in the liquid rock expand like a soda shooting from a sealed bottle that has been shaken hard and opened suddenly, causing a volcanic eruption.

This process is not happening on the eastern coast of these two continents where the seashore goes at a gentle slope into the sea.