Sanctuary Integrated Monitoring Network
Monterey Bay National Marine Sanctuary
Geology_ map
Figure 1. Seafloor substrate (hard and soft habitat) within the Monterey Bay National Marine Sanctuary. [View Larger]
The diverse geologic features of the Monterey Bay National Marine Sanctuary are controlled by dynamic processes that can significantly influence ecosystems and habitats. For example, natural hazards such as earthquakes, erosion and submarine landslides play an important role in shaping the coast and seafloor.

These shifts in the sanctuary's geologic character can affect both the location and size of habitats for many marine plant and animal species. Therefore, mapping geologic features and understanding the processes that shape them is essential to recognizing and interpreting change in the sanctuary.

The San Andreas Fault System traverses the sanctuary in a northwest-southeast direction and controls much of the overall geologic character of the region. This series of sub-parallel faults forms the boundary between the Pacific and North American tectonic plates, the former of which is sliding northwest several centimeters per year relative to the latter. In the vicinity of the sanctuary, the San Andreas Fault System is comprised of: Movement along these faults causes earthquakes and helps to shape the surrounding landscape: coastal mountains are thrust upwards, submarine canyons are channeled and underwater landslides are triggered.

A recent study by the United States Geological Survey (USGS) determined that there is a 62 percent chance of a magnitude 6.7 or greater earthquake occurring on one of the faults in the greater San Francisco Bay Area between 2003 and 2032. In this time period, there is a 10 percent chance of a magnitude 6.7 or greater earthquake on the San Gregorio Fault and a 21 percent chance of a similar earthquake on the San Andreas Fault.

Coastal cliffs with arch formed in sandstone.

A view of the interesting geology at a State Park site just north of Ano Nuevo.

Monterey Bay, one of the sanctuary's most prominent features, formed as wave action and sea-level rise eroded weaker rocks and sediment of the inner bay, while the stronger sedimentary rocks of Santa Cruz and the granitic rocks of Monterey resisted erosion and became headlands. The concave structure of Half Moon Bay and San Simeon Bay formed in the same manner, with only one defining headland.


Important focus areas for monitoring efforts in the sanctuary include coastal erosion, the continental shelf and submarine canyons.

Coastal Erosion
A significant amount of development and infrastructure is threatened by coastal retreat, and coastal erosion can impact habitats, such as kelp forests and bird nesting grounds on beaches. Highlights from recent studies of coastal erosion in this area are described below: The Continental Shelf
Geology in Santa Cruz
Another important geologic feature is the continental shelf, the shallowly-dipping, submerged extension of the continent that extends to approximately 120 meters' water depth and varies greatly in width along the length of the sanctuary. The shelf is covered with mud, sand, gravel and rocky outcrops that provide ecological niches for marine species.

Mapping the shelf's geology and characterizing how it changes over time is essential to understanding sanctuary habitats. Because of the expense and technical challenges of underwater mapping, this research often requires collaboration among several organizations, including the USGS, the Monterey Bay Aquarium Research Institute (MBARI), California State University Monterey Bay (CSUMB), Moss Landing Marine Laboratory (MLML), UCSC and others.

Examples of continental shelf mapping projects in the region include the following: Submarine Canyons
Within the center of Monterey Bay is the Monterey Submarine Canyon, the largest of a set of canyons that dissect the continental shelf, delivering huge sediment loads via turbidity currents down the continental slope to the abyssal plains of the deep ocean. The Monterey Submarine Canyon is comparable in depth, gradient and length to the Grand Canyon of Arizona; it constitutes a unique deep-water habitat relatively close to shore.

Other large canyons in the area include: Measuring the sediment-laden currents that carve these canyons is a difficult task because of the episodic nature and immense size of the flows. Researchers have successfully documented turbidity currents in recent years, as described below:
Follow the Monterey Bay National Marine Sanctuary on Facebook go to facebook and Twitter go to twitter