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Seabright Beach Building

A cache by TerryDad2 dedicated to 50sumtin Send Message to Owner Message this owner
Hidden : 08/26/2008
1.5 out of 5
1.5 out of 5

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Geocache Description:

Prior to the construction of the Santa Cruz Yacht Harbor Jetty, waves crashed against the cliffs of this beach, similar to cliffs further north. The Jetty has stopped the southward migration of sand along the coast, forming this wide sandy beach. Touchstone is the contact person for this Listing. Clicking on the Cache Owner hyperlink will take you to Touchstone's Profile, and you can submit email answers to him.

This is a State Beach. There are various free parking options on top of the cliffs. Then you will need to make your way down the cliff to the coordinates.

Seabright Beach owes its existence to the Santa Cruz Yacht Harbor Jetty. Prior to the 1960s this shoreline looked similar to the beach cliffs further north. Waves pounded directly against the base of the cliffs eroding out a marine terrace (see Marine Science Earthcache.)

Sand was prevented from building up along the shore by a current southward created by the waves approaching the shore at an angle. When waves approach the shore at an angle they generate a current parallel to the shore called the longshore current or littoral drift. At various points along the shore, the water in the longshore current returns back to the ocean in rip currents. Rip currents are fast moving currents that move directly out to the ocean. The result is the transport of sand southward along the coast. Because of the relatively high energy of the waves along this section of coast, the sand moved very quickly down the coast, never building up as a beach. Photos from the 1900s (found in the USGS Open-File Report 00-438) looking north from near the Santa Cruz Yacht Harbor Jetty shows the waves pounding the base of the cliffs of this beach. The sea stack at the coordinates is in the picture just below the arrow pointing at San Lorenzo Point.

This southward transport of sand was interrupted in the 1960s by the construction of the Santa Cruz Yacht Harbor Jetty. This jetty sticks out into the ocean blocking the longshore current and sand began piling up behind it. This created one of the widest beaches in the Northern Monterey Bay. A photo from 1975, also from the USGS, taken from the same location shows this growth of the beach. The house on the right side is the same in both pictures.

One of the examples that shows the beach widening is the burial of a sea stack at the northern end of the beach. A sea stack is an isolated column of rock that is the remnant of a sea cliff, arch, or headland. Photos from the 1890s (found in the USGS Open-File Report 00-438) show this sea stack being pounded by waves a short way off the coast. Today the coordinates bring you to the same sea stack buried in the beach sand.

The amount of burial changes seasonally since sand on the beach is constantly being moved around. As you can see, each wave that comes in pushes around the sand on the beach, turning the ocean water at the shore brown. The difference in energy between summer and winter waves drastically changes the look of the beach. To examine this seasonal change, it is good to have names for the different parts of the beach. In this case, we’ll look at three parts, the backshore, the foreshore, and offshore.

The backshore begins at the vegetated cliffs to the high tide level and is comprised of the berm and berm crest. The berm is the relatively flat sandy area where everyone loves to put their beach towels. At the berm crest, beach slopes more steeply to the high tide level. The width of the berm changes seasonally. During the summer it is wider than during the winter. This change in width results in the moving shoreward or seaward of the next two zones. The foreshore begins at the high tide line and stretches to the low tide line. This section of beach in usually slopes downward at a uniform level. Because of the tides, this section of beach is periodically below sea level or above sea level.

Beyond the foreshore is the offshore beginning at the low tide line and extending off shore. This section of the beach is always below sea level but constantly affected by the waves. The offshore profile changes seasonally. During the summer, it is a relatively uniform slope down. During the winter, a trough (low point) forms with mounds of sand (bars) eroded from the berm shoreward and seaward of the trough.

The seasonal changes noted above are caused by the different energy levels of summer and winter waves. Winter storms generate shallow waves with more energy than summer waves. The winter waves erode sand off the beach and store it in offshore bars.

The winter waves are generated by local storms. They form large waves that do not extend deep beneath the ocean surface. Thus as they crash on the shore they have enough energy to pick up sand and pull it off of the foreshore into deeper water where the shallow waves do not reach. The largest storm generated waves also erode the face of the berm crest, reducing the width of the berm. The sand is then deposited in sandbars off-shore.

During summer, the waves are generated by storms far out to sea. These waves are milder but because they have been traveling across the ocean, they have developed into deeper waves. As these waves come to shore they pick up the sand that was deposited int he off-shore sand bars and transport it back onto the foreshore. As the water flows back to the ocean, there is not enough energy to transport as much sand as the wave brought onto the forshore back off shore, resulting in a net gain of sand. This results in the gradual build up of the berm crest and the berm widens for the summer.

Since the sea stack is near the foreshore, the amount of burial could change seasonally.

Logging requirements:
Send me a note with :

  1. The text "GC1FMND Seabright Beach Building" on the first line
  2. The number of people in your group.
  3. Estimate the height of the sea stack that remains unburied at the time of your visit. (This should change seasonally). Put this in your "found it" log.
  4. Using your gps, at the time of your visit determine the width of the beach along a line perpendicular to the shore from the base of the cliffs, though the sea stack to the water. (Yes, the tides will change this measurement by a few feet, but seasonal changes should still be seen).Put this in your "found it" log.

The above information was compiled from the following sources:

  • Cheryl Hapke, GEOLOGY AND COASTAL HAZARDS IN THE NORTHERN MONTEREY BAY,CALIFORNIA FieldTripGuidebook November4,2000 Open-FileReport 00-438, USGS
  • Office of Naval Research; Habitats: Beaches - Characteristics;

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