the foreshore - the area most influenced by the high and low water marks and breaking waves. the backshore - submerged only during the highest tides and severest storms. the berm – the high point on the beach; the backshore-foreshore boundary. It changes seasonally. Landforms and terminology in coastal regions
Berm Beach face Notch Wave-cut bench Longshore bar
Light versus heavy wave activity Light wave activityHeavy wave activity Berm/long- shore bar Berm grows and longshore bars shrink Longshore bars grow and berm shrinks Wave energyLowHigh Time spanLongShort CharacteristicsSummertime beach: sandy, wide berm, steep beach face Wintertime beach: rocky, thin berm, flattened beach face
Summertime and wintertime beach conditions Summertime beachWintertime beach
Movement of sand on the beach Movement parallel (↔) to shoreline –Caused by wave refraction (bending) –Each wave transports sand either upcoast or downcoast –Huge volumes of sand are moved within the surf zone –The beach resembles a “river of sand”
Erosion Deposition Human Development
Longshore current and longshore drift Longshore current = zigzag movement of water in the surf zone Longshore drift = movement of sediment caused by longshore current
Features of erosional shores Headland Wave-cut cliff Sea cave Sea arch Sea stack Marine terrace
Headland Eastern tip of Oahu
Wave-cut Cliff Ka‘ula
Sea Cave w/collapsed roof Na Pali Coast, Kauai
Sea stack (collapse of sea arch) Sea arch Puu Pehe (Sweetheart Rock) on the island of Lanai. Chain of Craters Rd., HI
Sea Arch and Sea Stack
Marine Terrace Haunama Bay
Features of depositional shores Spit Bay barrier Tombolo Barrier island Delta
Spit
Barrier Bay
Tombolo Poipu Beach Park Kauai
Formation of barrier islands Sea level rose after the last Ice Age Caused barrier islands to roll toward shore like a tractor’s tread
Barrier Islands Features: 1.Ocean beach 2.Dunes 3.Barrier flat 4.High salt marsh 5.Low salt marsh 6.Lagoon
Barrier Beaches Red Sands Beach, Maui
Barrier Islands
Deltas Feature: Triangle deposit of sediment Mississippi Delta Nile River Delta
Features of Submerging Shorelines Changes in Sea Level: Tectonic movement Isostatic adjustment Worldwide (eustatic) changes in sea level Ice ages Global warming
Composition of Beach sand in Hawaii: Coral Shells Sponge spicules Calcareous algae Volcanic particles Shark teeth
White Sand Beach
Black Sand Beach Big Island
Green Sand Beach Big Island Mahana Bay, HI
Red Sand Beach Maui
1.An abundant supply of loose sand in a region devoid of vegetation 2.A wind energy source sufficient to move sand grains 3.A topography whereby sand particles lose their momentum and settle out
Vegetated dune, Kanaha, Maui. Naupaka shrub and 'aki'aki and pohuehue (with purple flowers) ground cover at center, 'aki'aki (sparse ground cover) in background.
Close up of 'aki'aki. Photo from JOHNSTONE, Close up of 'akulikuli. Photo from JOHNSTONE, Close up of pohuehue, Honokahua, Maui Common name: beach morning glory
Sea-Level Rise Wave/Current Action Coastal Erosion Sediment Deficiencies Sand mining Dune grading Sand impounding (behind shoreline structures) Water quality degradation Harbor/navigational channel construction
Types of hard stabilization Hard stabilization perpendicular to the coast within the surf zone: –Jetties—protect harbor entrances –Groins—designed to trap sand Hard stabilization parallel to the coast: –Breakwaters—built beyond the surf zone –Seawalls—built to armor the coast
Shoreline Hardening: Groin
Shoreline Hardening: Jetty
Shoreline Hardening: Breakwater Magic Island is a peninsula shooting off from Ala Moana Park. The beach is protected by a man-made breakwater that cuts off the action of the surf while allowing enough water circulation to keep the salt water fresh and clean.
Shoreline Hardening: Seawall Waikiki Beach from the Halekulani Hotel.
Lanikai
Beach Replenishment Kohio Beach 10,000 cubic yards of sand pumped from off shore
Beach Replenishment Kohio Beach
Beach Replenishment Kohio Beach
Before After Beach Replenishment Kohio Beach
Beach Replenishment Kohio Beach Before After
Reasons to Protect Hawaii's Beaches Multi-billion dollar visitor economy They are critical in flood and erosion prevention They are a part of Hawaii's culture and heritage. Beaches and dunes are important elements of our shoreline environment and are critical to the health of the coastal marine ecosystem.
Inquiry 1.Types of hard stabilization include:_____. 2.Is there a way to slow down erosion without using hard stabilization? 3.Beach sand from Hawaii is composed of _____. 4.How is a sea stack formed? 5.What are some key characteristics of plants living on dunes?