sink under (something)
1. To fall or submerge beneath some surface. The boat was struck with another torpedo, and it sank under the waves. The frozen lake became unstable, and the man sank under the ice.
2. To fall, descend, or collapse due to some downward pressure or force. The entire roof sank under the strain placed on it by the accumulating snowfall. The hot air balloon began to sink under the weight of so many people.
sink under (something)
to submerge. The small boat turned over and sank under the surface. It sank under and went straight to the bottom.