Oceanic crust spreads at ____1_______, creating new crust and slowly enlarging the ocean basin. _____2_______ are deep valleys at passive continental boundaries. They are likely eroded by ____3____, which occur when sediment-laden water rapidly moves down slope. Melt from the subducting plate rises to the surface, erupts through the crust on the overriding plate and forms _____4_______ on continents, or ____5________in the ocean.