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.”
Sand deposition
If the sediments
are…
very fine sand
sand
cobbles
boulders
then they were
deposited by
wind
small waves
big waves
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
Longshore Drift vid
consists of the transportation of sediment along a coast at an angle to
the shoreline. It is dependent on:
1. direction of the 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…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 habitats
Headlands – 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
Boulder
Cobble
Pebble
Granule
Very coarse sand
Coarse sand
Medium sand
Fine sand
Silt
Clay
Sediment size (mm)
>265
65-265
4-64
2-4
1-2
0.5-1
0.25-0.5
0.07-0.25
0.25-1/256
<1/256
Average beach slope
irregular
19°-25°
13°-19°
11°
9°
7°
5°
5°
<5°
<5°
THE END