Sand itself is produced by a sequence of dynamic processes. Rocks eroded far up rivers and streams are shattered and ground as they are carried down to the sea. There they are passed to the current of the ocean shore, where they join the debris of rocks and shells broken by the pounding energy of the surf.
The fine particles we call sand are grains of quartz and feldspar mixed with other minerals. Light enough to be suspended in turbulent waters, sand is carried down the coast by the nearshore currents. It is deposited whenever the wave energy and the particles can settle to the bottom. The composition of sand varies, depending on the local rock sources and conditions.
Sand is continously moving and is exposed to erosion. In earth science, erosion is the action of surface processes such as water flow or wind that remove soil, rock or dissolved material from one location and then transport it away to another location. The particulate breakdown of rock or soil into sediment is referred to as physical or mechanical erosion. This is the type of erosion that happens at Santa Barbara beach. Chemical erosion hardly happens here.
The nearshore currents off Santa Barbara's south-facing beaches moves from west to east. The waves generally strike at the beach at an angle, continually stirring up and dropping sand. Overall, current gradually carry sand past Santa Barbara and beyond Ventura where it eventually falls into an undersea canyon off Port Hueneme's shores.
By observing the beach over time, you can detect an annual cycle which is special in this region. This is mainly due to the location of Santa Barbara (east-west) while the other parts of the North American Pacific coast is north-south. Du to the orientation of the shoreline, the waves strike at the beach in a different angles compared to other regions with sandy beaches. During summer the relatively small, low-energy waves deposit sand at their upper reaches, extending the beach toward the sea. Winter storms generate large, high-energy waves which stir up the sand and carry it offshore, sometimes exposing the rock.
Human activities can interfere with these cycles. Damming of the rivers reduces the flow or sediment into the nearshore current. Structures like the Santa Barbara breakwater can interfere with sand movement along the shore. When it was built in 1929, the break water jutted into the nearshore current, slowing water movement and causing deposition of sand. Eventually a wide beach (Leadbetter Beach) formed. Then the nearshore current carried most of its sand load around the breakwater's end, where some of the water swirled in a low-energy eddy. The sand settled out of the current, forming the sandspit at the harbor mouth in only a few years. This settling continues today, and the harbor is regularly dredged to keep the sand from building up to block the harbor mouth completely.
To claim a find for this earth cache, please send me the answers to the following questions:
1) Do you think that the sand is deeper in summer or winter time? Please give reasons for your answer.
2) In which time of the year does the beach suffer from a strong erosion?
3) You are standing on the Stearns' Wharf. Look around you. What does the city of Santa Barbara do to reduce erosion on the beach?
Optionally you can upload a picture of yourself or your GPS at the earth cache coordinates.
Have fun exploring geology!
Sources:
Santa Barbara "Places of Geological Significance" about Shifting Sands
Wikipedia information about sand and erosion