Chapter 12 Notes:

Like rivers and glaciers, winds are great agents of erosion!

• Winds pick up and move sediment
• Winds can drive sediment against other rocks

Dust storm - When great amounts of fine sands and silts are lifted and blown from the topsoil

Abrasion of Materials

• Silts and clays are too soft to cause weathering
• Sands are coarse enough to wear away at the rock and cause weathering
• Sands can wear away at almost anything they hit!
• Ventifacts are formed from the sand blasting away at the rock, forming unique shapes

Deflation is a term that describes the removal of loose rock particles by the wind.

• Produces "desert pavement"
• Only the coarse sands and gravels remain forming a hard, rocky layer on the soil surface
• When total deflation happens, "blowouts" form hollows in the sandy soil.
• Some blowouts even form into desert oasis

Winds can even deposit material; not just remove it.

• Winds produce "Loess" - silt material that is usually yellowish in color
• Its angular form allows for walls of Loess to form that can be up to 100 meters high
• Loess can be found in the US, Europe, and northern China

Sand Dunes

• Hills of sand deposited by winds
• Form wherever strong winds occur
• Windward - the side of the dune against the wind
• Leeward - the "backside" of the dune
• Example: Winds blowing steadily from the west will form a dune with a gentle slope on their windward (west) side and a steep slope on the sheltered leeward (east) side.
• Shape of the dunes depends on supply of sand, strength of wind, and amount of vegetation
• Barchans - strong winds with limited sands
• Transverse - strong winds with lots of sand
• Parabolic - form around blowouts
• Longitudinal - form when winds shift directions
• (See pictures on page 213!!!)

Winds and waves

• Depends on the fetch of the water (distance across the body of water)
• Since lakes are smaller than oceans, they will not produce larger waves than oceans
• Whitecaps form when the waves are strong and tall; when the waves falls over on itself
• Swells are formed from gentle, steady movement of water
• Wave height - difference between the waves high point (crest) and its low point (trough)
• Wavelength - distance from one crest to the next
• Stong winds produce long wavelengths
• On the oceans - wavelength is 20-30 times the height
• The period of the wave is the time it takes one wavelength to pass a given point.
• Speed = wavelength divided by period

Why is it that when a wave comes to shore it seems to be at an angle, but when rolls up onto the beach, it comes up straight?

• Refraction occurs!
• The end of the wave closest to shore scrapes bottom first and slows down
• The other end further out continues on, causing a turning effect on the wave
• The wave then turns and hits the shoreline straight on rather than at an angle
• Waves wear away at an uneven shoreline and create a smoother shoreline
• Waves will hit the shoreline that sticks out the furtherest (headlands) and will weaken prior to striking the inland shoreline (cove).
• The waves will eventually create a smooth shore

Shoreline Currents

• Motion of water up a beach is called Swash
• Motion of water down a beach is called Backwash
• Strong backwash is often consided Undertow which will drag material back into the deeper water
• Rip Currents are strong surface currents that flow away from the beach
• Rip currents can pull swimmers deeper out to see, causing panic, then drowning! Swim parallel to shore and you will survive!

Shoreline Features

• Sea Cliff - forms where the sea water wears away at the shoreline and rock face
• Sea Cave - forms when softer rocks on the bottom of a sea cliff are worn into a hollow in the rock
• Sea Arch - when water breaks through a sea cave to form an arch
• Sea Stack - the walls of the sea arch that stand after the sea arch collapses

Sandbars

• Longshore currents carry enough sand and pebbles to form a sandy bar in the shallow ocean waters
• Sandbars connected at one end to the headland is called a Spit
• When the spit grows completely across the bay and connects to the other side, it is called a Baymouth Bar
• A spit with a curved end is called a Hook
• Sandbars protect the water behind them, referred to as a Lagoon
• When sandbars form that are not attached to the shoreline on either end, they are called Barrier Islands
• All of these sandbar features are not permanent.
• A Beach is defined as the area of land between high tide and low tide
• Fiords form when water floods glacial troughs and are found mostly in northern Europe
• Corals can form into a variety of reefs:

1. Fringing reefs grow close to shore
2. Barrier reefs grow further out to sea
3. An Atoll is formed when coral form a ring-shaped island in the ocean waters.