HALF MOON BAY, Calif.  The image of the quintessential American surfer  a bronzed slacker in board shorts  may be firmly entrenched. But that surfer dude bears little resemblance to the athletes known as big-wave surfers, a small community composed of men and women who often become amateur oceanographers and experts in wave dynamics in order to ride waves that can be more than 50 feet high.

On Saturday, this community will gather here for the Super Bowl of big-wave surfing: the Mavericks Surf Contest, which pits 24 surfers against one another  and against some of the most treacherous surfing conditions in the world.

An underwater rock formation is partly responsible for the spectacular breaks that can result in towering walls of water, which can deliver harsh punishment to the surfers if they wipe out. Mark Foo, a legendary big-wave surfer from Hawaii, died while trying to surf Mavericks in 1994. So big-wave surfers must do more than wax their boards and wait for waves.

In addition to maintaining a supreme level of physical fitness, they study weather patterns, listen to radio broadcasts by the National Oceanic and Atmospheric Administration and do whatever else it takes to understand the water’s movements.