The Beach, A River of Sand River of Sand Video

Berm: the nearly horizontal portion of the beach on the backshore formed by the deposition of sand

Where does sand come from?

From where do beaches come? Sand, along with gravel, silt and clay are collectively known as sediment, and are produced by the mechanical and chemical breakdown of rocks. Once disaggregated from the original source rock, this material is then eroded and transported by either wind, water, or ice, often ending up at the deposits of rivers or lakes, as sand dunes, or ultimately as sediment in the sea.

What about when there are no mountains? In areas where there is no good source of sedimentary material from mountains or volcanoes, sand is often entirely composed of organic material i.e. shell fragments, coral, and the tests (skeletons) of small planktonic organisms. The sand is said to be “biogenic.”

Sand deposition If the sediments are… then they were deposited by very fine sand wind sand small waves cobbles big waves boulders glaciers

La Jolla, California Summer Beach Gentle waves pile sand on the beach

La Jolla, California Winter Beach Strong waves carry sand off the beach depositing it temporarily on off-shore sand bars

The shape of the beach is determined by how it formed… Why is it better to surf in the winter?

it is all about sand movement

Sand created features

Longshore Drift consists of the transportation of sediment along a coast at an angle to the shoreline. It is dependent on 1. direction of the prevailing wind 2. swash (turbulent water that washes up on the beach) 3. backwash (offshore flow of water)

Natural Sand Deposition Features

What’s happening to Block Island?

a local tombolo

a local spit

Local barrier beaches on south shore

Some features are directly created by man

Rip Currents Bands of fast moving water moving off shore Look for a channel of choppy water with a noticeable color difference

DRAMATIC SEDIMENT FEATURES

Sea Arch

Sea Stack

Blow Hole blow hole Hawaii

Common constituents of sand: Minerals: Quartz : clear (doesn’t break down easily) Feldspar : pinkish-tan Mica: black and flaky Olivine : olive Hornblende : black/grey, dull Garnet: reddish Biogenic: Coral Shells Foraminifera Coralline algae Rock: Volcanic basalt (black islandic rock) Granite

How oceanographers analyze sand… Color  composition Rounding  distance traveled or age Size  strength of waves, wind, glacier Pits  directly from volcano Sorting  distance traveled, # of sources of material

… so scientists also know about the beach’s location by… it’s steepness (from size) what the parent material is (color) distance the sand traveled to get there the power of the beach’s waves (shape) biogenic material…continental or island, tropical, temperate or polar The influence of man (?)

Wentworth sediment size scale, and resultant beach shape, for example Sediment size (mm) Average beach slope Boulder >265 irregular Cobble 65-265 19°-25° Pebble 4-64 13°-19° Granule 2-4 11° Very coarse sand 1-2 9° Coarse sand 0.5-1 7° Medium sand 0.25-0.5 5° Fine sand 0.07-0.25 Silt 0.25-1/256 <5° Clay <1/256

What can you tell?

Beaches are important habitats Headlands – Point Reyes, California Look!

Elephant Seals

“Haul Out” to molt

beachmaster battle

FUN with sand!!

THE END