Coastal & Arid Geomorphology Lab 9

Coastal Geomorphology Concepts Principal Forces for Erosion (5) Landforms Barrier Island/Lagoon Barrier Spit Beach Coral Reefs Tombolo Wave-cut arch & platform

1. Tides Oscillations of ocean water: gravitational pull of the Moon and Sun 24 hours: High-Low-High-Low tide periods 2. Sea-level changes  Rising/Falling results from tectonic activity or amount of water in ocean  Creates emergence (above water) and submergence (below water) coastlines Coastal Geomorphology Principal Forces for Erosion

Coastal Geomorphology Principal Forces for Erosion (con’t) 3. Waves Most important erosional force 4. Currents Large volumes of water moving horizontally Consistent winds create currents “Longshore” currents transport sediment down a coastline (helps in formation of beaches) 5. Stream Outflows Spills sediments out into the ocean and adds material to beaches Deltas often form at the mouth of rivers – why?

Coastal Geomorphology Landforms: Barrier Islands/Lagoons Barrier Island Long, narrow, low island that lies parallel to a shoreline. Buffers the mainland from storms and large waves. Lagoon Nearly isolated body of water, separated from sea by the barrier island. Low-energy waves and relatively calm area, so sediments may accumulate. Mudflats, marshes, swamps

Coastal Geomorphology Landforms: Barrier Spit Barrier Spit Coastal barriers that extend into open water, attached to the mainland at one end. Can develop into a barrier island if it becomes separated from the mainland.

Coastal Geomorphology Landforms: Beaches Beaches Made of eroded continental material (sand, gravel, rock fragments) that are washed to the sea by streams. Sediment gets suspended in sea water and is often transported further down the coastline by longshore currents. Longshore currents provide a continual onshore-offshore movement which pushes the sand along the beach edge. Often called “littoral drift.”

Reef formation first determined by Charles Darwin, mid-1800s. Occurs in tropical zone – approx 30 o N to 30 o S. More coral species live in the Pacific than anywhere else! Fringing Reef Forms along shoreline of volcanic island (hot spot) – it likes the warm waters! Barrier Reef Island begins to sink or erode, but reef continues to grow upward. Lagoon is created between the top of the reef and the sinking island. Atoll Island sinks/erodes below sea level, reef continue to grow upward. If a “broken circle” of reef, it is likely due to storm action. Coastal Geomorphology Landforms: Coral Reefs

Coastal Geomorphology Landforms: Tombolo Tombolo A narrow piece of land between the shore and an island, or between two islands. Forms because wave refraction around islands causes sand and sediment to build up in a linear formation where the waves meet (around the backside of the island). Goat Rock Beach, CA

Coastal Geomorphology Landforms: Wave-cut Arches & Platforms Wave-cut Arches Formed by wave action which erodes less-resistant rock from an outcrop. Wave-cut Platforms Formed after waves hit against a cliff face, causing undercutting. Most obvious at low tide when they become visible as huge areas of flat rock. An “extreme” environment (for marine life) because of continual wave action. ARCH PLATFORM

Deserts & Arid Geomorphology Concepts Locations Typical Conditions (4) Principal Forces (2) Landforms Alluvial Fan/Bajada Inselberg Playa Buttes, Pinnacles, Mesas Dunes

Deserts & Arid Geomorphology Locations 0o0o 0o0o 0o0o 0o0o

Desert & Arid Geomorphology 4 Typical Conditions Sparse cover of vegetation and soil Bedrock is exposed Impermeable surface layers This increases the erosion potential of rainstorms! Rain is infrequent, but short-lived & intense Causes dry streambeds to fill quickly & flow rapidly Flash flooding = fast erosion! Interior drainage = centripetal Ephemeral streams flow to the bottom of basin Alluvium is deposited and water evaporates, sometimes leaving behind a salt layer

Deserts & Arid Geomorphology Principal Forces for Erosion 1. Water Water may be scarce, but rain/thunderstorms are often intense. Rivers or floodwaters cut into the landscape, often creating canyons. 2. Wind Often removes sand/silt from areas, exposing bedrock to the erosional power of water.

Desert & Arid Geomorphology Landforms: Alluvial Fan Alluvial Fan  When streams come out of steep canyons… the velocity of the stream drops dramatically, and… the slope of the river decreases. Therefore, alluvium is deposited! Edges of the fans may be clearly defined.  Bajadas are formed when multiple alluvial fans join along a mountain front

Desert & Arid Geomorphology Landforms: Inselbergs & Playas Inselberg Isolated hill/ridge, steep-sided Formed when less-resistant material is eroded away from more-resistant rock (often an intrusive formation). Example: Uluru (Ayers Rock), AU Playa Dry lake bed Found at lowest point of basin Recognizable by dried mud, often covered w/ crust of salt

Desert & Arid Geomorphology Landforms: Pinnacles, Buttes, Mesas Pinnacles Isolated hill with steep sides and pointed or flat top “Caprock” (resistant) remains while softer rock is eroded away Typical of southwest U.S. Buttes Larger than a pinnacle, flat top Example: Chimney Rock, NE Mesas Larger than a butte, smaller than a plateau. Flat top.

Desert & Arid Geomorphology Landforms: Sand Dunes Shape & formation depends on… Amount of sand available Persistence & direction of wind Presence of vegetation  With little vegetation: can be movement over time 4 main shapes Barchan Transverse Longitudinal Blowout

Desert & Arid Geomorphology Landforms: Sand Dunes Barchan Limited supply of loose sand Crescent-shaped “Horn” points downwind Wind blows constantly in a single direction Migrates downwind over long time Which way is the wind blowing?

Desert & Arid Geomorphology Landforms: Sand Dunes Transverse Less uniform than Barchan More supply of loose sand Maintains general crescent shape Usually forms interconnected ridges of sand

Desert & Arid Geomorphology Landforms: Sand Dunes Longitudinal a.k.a. “Seif” Wind directions shifts back & forth Long parallel ridges Egypt

Desert & Arid Geomorphology Landforms: Sand Dunes Blowout Wind erosion Scoops out sand and rock, creating closed depressions Depressions may fill with water