Chapter 15Section 2

Beaches

• Beach- an accumulation of sediment found on the landward margin of an ocean or lake.

• Berm - the dry, gently sloping zone on the backshore of a beach at the foot of a coastal cliff or dune.

Beaches• Shore - Area that extends between the lowest tide level and the

highest elevation on land that is affected by storm waves

• Shoreline - the line that marks contact between land and sea

• Coastline - marks the coast's seaward edge, while where the coast actually ends is hard to tell (actual coast extends until there is no more sea life)

• Beach Face - the wet, sloping surface that extends from the berm to the shoreline.

-may extend for several hundred km

-one or more berms

-irregular coasts confined to waters of bays

-can be composed of quartz grain and other minerals

-crushed shells and remains of marine life

-basaltic lava from volcanic islands

Beaches

• Composed of whatever material is found locally and abundantly

-derived from erosion of adjacent cliffs or nearby coastal mountains

-or by sediment delivered by coastal rivers

• Position of the shoreline migrates

• Beaches always being moved by waves and currents

-material in transit along shore

• Foreshore - Area exposed when it is low tide and submerged when it is high tide

• Backshore - Landward of the high-tide shoreline. Only touched by waves during storms.

• Nearshore zone - lies between low- tide shoreline and line where waves break at low tide

Beaches

• Offshore zone - Seaward of the nearshore zone

Factors that Influence Wave Characteristics

• Ocean waves are:

-Traveling along the interface between ocean and atmosphere

-Energy traveling through a medium (water)

-Most are initiated by the wind and provide the energy that shapes and modifies shorelines

• Smaller breezes cause wavelets to appear while at greater wind speeds more stable winds form and advance with help from the wind

• The more wind/energy produced equals steeper waves

• Waves:

-Crests- top of the waves

-Troughs- separate the crests (lower part of the wave)

-Whitecaps- Waves that grow so tall that they topple over and form ocean breakers

Factors that Influence Wave Characteristics

-Still water level- halfway between the crests and the troughs. This is the level that water would occupy if there were no waves.

-Wave Height- Vertical distance between trough and crest

-Wavelength- horizontal distance between successive crests or troughs

-Wave Period- Time it takes one full wave (or wave length) to pass a fixed position

• Three factors that influence wave height, length, and period: -Wind speed

-Length of time wind has blown

-Fetch-distance that wind has traveled across open water

• Maximum fetch and duration of wind beyond which waves will no longer increase in size

-Swells- lower in height and longer in length and may carry a storm's energy to distant shores (symmetrical/ termed this when they have left the storm area)

Wave Particles in Motion

• Circular Orbital Motion - An object on the surface of the water experiences a slight forward and backward motion. Energy is transmitted through this.

• Each particle of water transfers its energy to the next

• Creating a circular transfer of energy

• Goes to depth equal to half of the wavelength

• Wave Base - Depth exactly half the wavelength (measured from still water)

Circular Orbital Motion

Wave Collapse

• When waves travel closer to shore, they begin to slow down, trying to compensate for the decreasing depth. The faster waves farther out catch up, making the waves decrease in length.

• When the speed and length of the waves decreases, they become higher.

• Break - Critical point where a wave is too steep to support itself, so the wave front collapses (breaks)

• Surf - Turbulent water created by breaking waves

• Swash - Turbulent sheet of water from collapsing waves

• Backwash - Water that flows back down the beach towards the ocean after the energy of the swash has been used up

Wave Collapse

• Wave erosion is caused by wave impact, pressure, and abrasion.

• Abrasion - The grinding and scraping of a rock by the friction and impact of rock particles carried by water, wind, or ice.

• Summer- light wave activity creates wide sand berm

• Winter- Strong wave activity leads to more erosion and this creates a narrow berm.

Wave Erosion

Wave Erosion

• Wave action often depends on weather, with larger waves during storms

• The pressure of Atlantic waves in the winter on the earth can reach 2000 lb per sq foot

• When waves hit a rock, water is forced into every opening

• The waves subside and air rapidly expands, dislodging rocks and enlarging fractures

• Waves also caused abrasion on beaches

Wave Refraction

Wave Refraction - The process by which a portion of a wave

in shallow water slows, causing the wave to bend and tend to align itself with underwater contours.

Wave Refraction

• Wave refraction affects the distribution of energy along the shore

• Influences where and to what amount erosion, sediment transport, and deposition will take place

• Waves often approach the shore at an angle, but when they hit shallow water, the front of the wave slows down and the part of the wave in deeper water is at full speed

• This causes the wave to crest and line up with the shore

• Because of this wave energy is concentrated against the sides and ends of headlands that project into the water

• Transports more pebbles and sand than beach drift

• Wave refraction along an irregular coastline- reach the shallow water faster than normal so the waves are bent more nearly parallel to the shore and hit it from 3 sides

• Therefore, the energy of waves is concentrated at headlands (erosion) and spread out in bays (deposition)

• In bays, sandy beaches can be formed

• Erosion and deposition will eventually straighten out an irregular shoreline

Beach Drift

• Most waves reach the shore at a right angle. (referred to as oblique waves because of the angle that they come into the shoreline)

• Beach Drift - Happens when the movements of the waves on a beach moves the sediment in a zigzag pattern along the beach.

• 5 meters to 10 meters of sand and pebbles are transported daily.

Longshore Currents

• Longshore Currents - Flow parallel to the shore (in the surf zone)

• Transport sediments along a coast at an angle to the shoreline• Amount of sediment transported is more than beach drift• Can change direction because the direction that waves

approach a beach changes with the seasons

Videos

An Overview

Video on the general ideas covered in this section.

Erosion and Landforms

Discusses erosion on the beach and its side effects.

thank you

from team 2

we would like to congratulate you on a wonderful session

*Mr. Koziol, we have a printed bibliography instead of a slide for it.