One of the most dangerous waves in the world
The Banzai Pipeline, or simply "Pipeline" or "Pipe," is a surf reef break located in Hawaii, off Ehukai Beach Park in Pupukea on O'ahu's North Shore. A reef break is an area in the ocean where waves start to break once they reach the shallows of a reef. Pipeline is notorious for huge waves which break in shallow water just above a sharp and cavernous reef, forming large, hollow, thick curls of water that surfers can tube ride. There are three reefs at Pipeline in progressively deeper water further out to sea that activate according to the increasing size of approaching ocean swells.
Specifics of the break
The reef at Pipe is a flat tabletop reef, with several caverns on the inside, creating a giant air bubble that pops on the front of the wave when the wave lurches upwards just before breaking. There are also several jagged, underwater lava spires that can injure fallen surfers. Sand can accumulate on the reef at Pipeline, and that can cause waves to "close out" (meaning the hollow tube of the wave collapses all at once and thus is impossible to surf). A strong swell (a formation of long-wavelength surface waves) from the west clears out the sand in the reef, and after that, a strong north swell can give rise to the best waves.
There are four waves associated with Pipeline. The left (which means the wave breaks from left to right from the perspective of a watcher on shore) known as Pipeline (a.k.a. First Reef) is the most commonly surfed and photographed. When the reef is hit by a north swell, the peak (the highest tipping-point of the wave where it begins to curl) becomes an A-frame shaped wave, with Pipe closing out a bit and peeling off left, and the equally famous Backdoor Pipeline peeling away to the right at the same time. As the size at Pipe increases, over 12 feet usually, Second Reef on the outside (further out into the deeper ocean waters) starts breaking, with longer walls (the unbroken face of the wave that the surfer slides across), and more size. At an extreme size an area called Third Reef even further outside starts to break with giant waves.