It's currently estimated that around 2,000 whales and dolphins are stranded each year. The majority of strandings result in death. Only about ten cetacean species frequently display mass beachings, with ten more rarely doing so.
“Cetacean stranding, commonly known as beaching, is a phenomenon in which whales and dolphins strand themselves on land, usually on a beach. Beached whales often die due to dehydration, collapsing under their own weight, or drowning when high tide covers the blowhole. Several explanations for why cetaceans strand themselves have been proposed, but none have so far been universally accepted as a definitive reason for the behavior.”