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El Niño Coastal Erosion Display
What to Look For


Landslides - look for circular or oval areas of erosion on steep slopes indicating the scar caused by a landslide. Commonly, as in the example at left, a depositional area occurs seaward, or downslope, of the erosional area where the failed material came to rest. (Landslides North of San Francisco, Location 1)


Rhythmic Patterns - Look for repeated patterns of erosional areas adjacent (in a longshore direction) to accretional areas. These are likely due to the presence of giant cusps in one of the surveys and either a) giant cusps in the other survey were not present or b) were shifted alongshore. During storms, wave runup in low embayments between adjacent cusps may attack dunes, causing net erosion, whereas landward of prominent cusps the dunes may be protected by the wide beach. (Umpqua River, Location 2)


Dune & Cliff Erosion - During severe storms, when runup can reach the base of cliffs and dunes, the wave impact leads to net erosion of the dune or cliff face which can be best observed in cross-shore profiles. In this example, the dune retreated landward 15 m during the El Niño winter. (Monterey Bay, Location 3)
Longshore Sediment Transport - look for a pattern where an erosional area is adjacent (in a longshore direction) to an accretional area, suggesting transport direction. In the example, transport is suggested from north to south with deposition occurring near the mouth of an inlet. These patterns are also pervasive at manmade structures designed for navigation and property protection, but also occur adjacent to natural irregularities in the coast, such as headlands. (Point Reyes, Location 1)


Overwash - look for a pattern where a depositional area occurs immediately landward of an erosional area, suggesting overtopping of the beach by wave runup. This results in erosion of the beach and net sediment transport (and deposition) landward. In this example, a low-lying spit was overwashed. This process occurs more extensively on the low-lying barrier islands of the East and Gulf of Mexico coasts, but there are many examples of overwash on the West coast during the 1997-98 El Niño winter as well. (Monterey Bay, Location 1)


River Breakthrough - look for a new channel eroded across the beach. (Monterey Bay, Location 2)