( CNN ) -- A shark attack Friday killed a 19-year-old college student off a beach on Vandenberg Air Force Base , said authorities in Santa Barbara County , California . A shark , described as being 14 to 20 feet in length , bit off the left leg of Lucas McKaine Ransom of Romoland , California , while he was Boogie Boarding with a 20-year-old male friend , said a spokesman with the Santa Barbara County Sheriff 's Department . Ransom was a junior at University of California at Santa Barbara . He was majoring in chemical engineering . On Friday morning , Ransom was riding the waves at Surf Beach about 100 yards offshore when a shark pulled him under the water , authorities said . His friend and other witnesses pulled him from the water , authorities said . Authorities released a photograph of the Boogie Board , showing a 13-inch bite mark . Air base fire personnel pronounced Ransom dead at the scene . Federal and state fish and game officials are trying to identify the type of shark . Surf Beach is one of three that sit on the coastal military base , and officials closed all three beaches at 9:46 a.m. Pacific ( 12:46 p.m . ET ) , shortly after the shark attack , an air base spokesman said . `` Our first responders were on scene to assist in rescue efforts , '' Col. Richard Boltz , 30th Space Wing commander , said in a statement . `` Our thoughts and prayers go out to the family and friends . '' The three beaches will remain closed for 72 hours , the spokesman said . Surf Beach is open to the public , but the other two -- Wall and Minuteman beaches -- are open to base personnel only , the spokesman said . The Santa Barbara County Parks Department is posting warning signs at beaches in the Jalama and Guadalupe beach areas , authorities said .
NEW : Authorities release photos of shark bite mark on Boogie Board . NEW : A man is bitten by a great white while swimming in the ocean off Florida. The California military base closes all three of its beaches after attack .