descending plate dives down it digs into the mantle here the colliding plates form a trench a giant crease in the ocean floor did seem that scientists had finally explained how the trench was formed mom there was just one problem: do a very large problem I around the world subduction zones cause violent earthquakes and catastrophic tsunamis we know seduction is happening because if the active earthquakes and these are the most devastating earthquakes home this is the earthquake that generated the tsunami in Sumatra also the other very large earthquakes in alaska and Chile home but the Marianas Trench the deepest subduction zone in the world hasn't caused the devastating earthquake since records began in the 17th century investigators needed to know why I that's that's the sixty thousand dollar question they hope the trenches shallower western edge might provide the answer old on here they found an intriguing chain underwater Hills two miles below the surface of the sea the new engineers drill down into the hills and collected core samples and when the scientists analyze the samples they discovered the hills were actually volcanoes when they spewed out not lobbed but much E the fine powdery mud is made up for the soft I love rock that has been ground up in the subduction zones it seemed this soft rock might explain why there have been no major earthquakes at the Marianas Trench the everybody has a sense that what up all klas but not all volcanoes erupting his rocks there some volcanoes that rap mud and a certain kind of unusual kind of my dad in the Marianas is made out a serpentine and serpentine is a very weak rocked and I can be scratched with the knife or something like that world investigators realized the grinding plates crush the softer rock to form a lubricating much that prevents large earthquakes then the mud bubbles up to the ocean floor where it forms the strange mud volcanoes found along the trenches western edge new other parts of the world like the Andes or maybe Indonesia you've got two plates that are grinding together and the one of the place is quite strong and it takes a big earthquake to rupture that played an amazing but if these rocks are weak like they are in the Marriott us we've got these for Pat Knight's those are very weak and it doesn't take much energy at all to get the two plates to glide one pass the other looking at last geologists have discovered what created the Marianas Trench used fifty million years ago the Pacific Plate slipped under the edge of the Philippine plate as it bends and dived into the Earth's mantle it formed the colossal Marianas Trench and the plate is still moving like a giant conveyor belt the earth's crust travel slowly across the pacific plate from its birthplace in the East Pacific bridge to its graveyard 10,000 miles away in the Marianas Trench today the Pacific plate movement can be tracked in real time confirmation