Giant faces. Swirling boils. Explosive speed. Huge peaks that pitch almost straight out.

Ever wonder what makes a Mavericks wave so unique and completely intimidating? A lot of it has to do with what's going on below the surface.

The California Ocean Protection Council and National Oceanic and Atmospheric Administration (NOAA) National Marine Sanctuary Program recently produced the most highly detailed imagery yet of the seafloor in the Monterey Bay National Marine Sanctuary, which includes the seafloor at Mavericks. For the first time, you can actually look beneath this monster wave, and get a glimpse of the awesome challenges it presents.

The California Coast State Waters Mapping Project has released highly detailed, three-dimensional mapping images, as well as an animated fly-through of the Mavericks seafloor (have a look below), which were produced using advanced sonar equipment. Included on this page are images and information taken directly from that survey.

Seafloor Imagery of Mavericks

This map shows seafloor bathymetric contours offshore from Pillar Point north of Half Moon Bay. The color gradient ranges from deeper water (blue) to shallow water depths (red). The Mavericks wave break is indicated by a black box offshore from Sail Rock.

The seafloor imaged off Pillar Point and Half Moon Bay is comprised of sedimentary rocks formed during the Pliocene, some 5.3-1.6 million years ago, and more modern sediments, primarily sand. Erosion by waves and currents have caused the weaker, less resistant beds to erode, leaving the stronger, more resistant beds elevated higher above the adjacent sediment-covered seafloor, resulting in the alternating striped pattern of higher ridges and lower troughs seen on the seafloor today. Movement along the San Gregorio Fault, which comes ashore in Pillar Point Harbor, has folded and uplifted the sedimentary rocks, causing the twists and turns in the seabed today, along with the headland at Pillar Point and the prominent east-west trending bedrock reef that is exposed above the water at Sail Rock.

Mavericks Wave Crests

In the image above, the blue lines show hypothetical large wave crests propagating in to shore from the west. As the waves move into shallow water, they begin to interact with the seafloor ("shoal") and their crests slowly bend to try to maintain their roughly parallel orientation to the bottom contours. The more the waves interact with the seafloor, the more they slow down and bunch up. Wave "rays,” or the pathways of wave energy, move perpendicular to the wave crests. In areas where the wave rays (and hence wave energy) diverges, the wave height decreases. Conversely, in areas where the wave rays (and hence wave energy) converges, the wave height increases. Due to the steep topography of the bedrock reef at Mavericks, the wave energy rapidly converges and the wave height rapidly increases, creating a huge wave compared to the adjacent areas.

The dominant wave direction off the central coast of California during most of the year is from the northwest. These waves propagate over the much gentler topography to the northwest of Sail Rock and are generally too small to shoal and break at Mavericks. Sometimes during the winter months, however, strong North Pacific storms generate large, long-period waves from more westerly directions that shoal and break over the bedrock reef just to the east of Sail Rock. The abrupt topography of the bedrock reef causes wave energy to converge over the reef, causing the wave to rapidly slow down, shorten in length and substantially increase in height relative to the areas just to the north and south of the east-west trending reef. This interaction of the geology and oceanography is what makes the wave at Mavericks so spectacular compared to many other locations along central California.

Fly-through Animation

The fly-through animation above begins approximately 1/2 mile offshore from Pillar Point north of Half Moon Bay. The area we are looking at in detail is a shallow near-shore reef in the vicinity of the San Gregorio Fault, a major active fault within the San Andreas Fault System. Motion on the fault zone has uplifted and deformed the rocks in the area near Mavericks into the S and J shaped folds we see on the seafloor.

The 3-D image is color-coded by depth: the blue and green areas are deeper than the areas in yellow and red. You can see how rugged the sea floor is in this area, with lots of ridges, valleys, chasms, and pinnacles.

The data indicates that Mavericks is above a portion of the rocky reef that is shallower than the surrounding rock. As a wave front approaches the shoreline and progressively enters shallow water, it becomes compressed and grows taller. The ridge promontory also has the effect of focusing wave energy, and the wave height rapidly increases, creating a huge wave compared to adjacent areas. About here (the highest red we see), the wave becomes unstable and breaks. In fact, the data collection stopped here because the rough sea conditions made it too dangerous for the scientists to operate their boat!

Although useful for explaining the mystery of Mavericks, scientists and resource managers will be using this data to identify hazards to navigation, classify different habitat types, locate biological hot spots, and study the San Gregorio Fault.

Significance of the California Coast State Waters Mapping Project and High-Resolution Mapping

The data illustrates the rugged seafloor conditions surrounding Mavericks, and helps better explain ocean ecosystems and underwater activities like giant Mavericks waves and earthquakes.

The data also:

• Helps us understand the unique aspects of our national marine sanctuaries, enabling better ecosystem-based management
• Creates images to educate future ocean scientists and foster citizen stewardship
• Identifies areas important to the California Marine Life Protection Act process
• Could help to predict seismic hazards along California's coast
• Charts navigational hazards such as hidden reefs and sunken obstacles
• dentifies geologic hazards along the seismically active California coast
• Documents the position and physical features associated with the marine segments of the San Gregorio fault in the Half Moon Bay area, a major active fault within the San Andreas Fault System.
Source: Sanctuary Integrated Monitoring Network - Comprehensive Study Available here.