The Beach, A River of Sand

River of Sand Video

Swash zone: area onto the beach that waves splash

Where does sand come from?

From where do beaches come?

• Sand, along with gravel, silt and clay are types of sediment– produced by the mechanical and chemical

breakdown of rocks.

• this material is then eroded by either wind, water, or ice– ultimately end as sediment in the sea.

What about when there are no mountains?

• sand can be 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.”

If the sediments are…

then they were deposited by

very fine sand windsand small wavescobbles big wavesboulders glaciers

Sand deposition

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

Longshore Drift vidconsists of the transportation of sediment along a coast at an angle to the shoreline. It is dependent on:

1. direction of the wind2. 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…why?

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

What can you tell?

Beaches are important habitatsHeadlands – Point Reyes, California

Look!

Elephant Seals

“Haul Out” to molt

beachmaster battle

FUN with sand!!

Sand detective investigation

Sand gives you clues to it’s beach’s location

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

Characteristics of sand oceanographers use to tell its origin:• Color composition• Shape (angular vs. round) 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, and thus power of the beach’s waves (from size of sand)

• what the parent material is (color)• distance the sand traveled to get there (sorting,

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 slopeBoulder >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 5°

Silt 0.25-1/256 <5°

Clay <1/256 <5°

THE END