how was the recent samoa tsunami caused?

in this particular location you have two oceanic lithospheric places colliding creating a divergent plate boundary. this means that one plate is being pushed under the other. the eath’s lithosphic plates don’t move all the time, but they do push constantly and build up pressure. eventually that pressure is enough to overcome friction and then they release all at once and move. this can cause the plate on top to get lifted up (uplift) rapidly (just a few seconds) which in turn lifts the ocean above it. that uplifted ocean water creates a wave that moves outward in all directions and travels hundreds of miles an hour. when this wave hits shore it is called a tsunami.