Coasts An N. Hardy powerpoint.

What we will learn. 1.Coastal zones 2.Types of coasts 3.Waves – how they define coast 4.Beach Currents 5.Coastal Features 1.Erosional Coast Features 2.Depositional Coast Features 6.Coast Linearization 7.Emerging/Submerging Coastlines 8.Human Intervention

Zones (Description) Backshore – Further inland from the shore Shore – Sand and low depth areas. Between shorelines. Consists of the littoral/intertidal zone. Nearshore – Beginning of the Continental shelf, where wave shoaling begins. Offshore – Begins at the continental slope, continues out from shore.

Zones (Pictures)

Types of coasts Major types: – Depositional Coast Deposit sediments Usually sandy – Erosional Coast Erodes away. Usually rocky Question for understanding: Which type of coast is the Huntington Beach Pier area?

Waves – How they define coasts High-energy coasts – Heavy wave activity, many storms – Usually erosional Low-energy coasts – Light wave activity, fewer storms – Usually depostitional Question for Understanding: Which type of coast is Huntington Beach?

Waves – how they define coasts Usually seasonal changes in wave activity A summertime beach Occurs more often in summer Low-energy weather, builds up berm A wintertime beach Occurs more often in winter High-energy weather, destroys berm Before removing this bar, guess which diagram is in summer and winter! Did you guess right?

Waves – Cool table w/ effects 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

Beach currents Wave movement linear to shore – Called a longshore current – Longshore drift/transport Movement of sediment by longshore current Create “upstreams” and “downstreams” of sediment movement on depositional beach – Why does longshore drift not occur further away from the shore? Because waves only effect the ocean beneath them to their wave base, which is ½ of the wavelength

Beach currents What is the mechanism for longshore currents? Water that rushes onto the beach: – Swash is water that soaks into the beach – Backwash flows back into the ocean Most water is backwash Backwash flows linearly down the shore

Beach Currents Rip Currents – Flow seaward – Caused when longshore currents meet and the backwash is greater than the incoming wave mass – REALLY COOL ANIMATION REALLY COOL ANIMATION – DANGER They kill people In order to escape, one must swim parallel to shore.

Coastal Features There are a lot. They are boring.

Coastal Features (Erosional Coasts) Headlands Rocky seaward outcroppings Wave Cut Cliffs – Waves cause water only up to a certain height on erosional coasts, when the rock above the notches cut into by the waves collapse, wave cut cliffs are formed Sea Caves -> Sea Arches -> Sea stacks – Sea Caves can change into arches and stacks over time Marine terrace Blow Hole – Outlet for sea caves

Coastal Features (Erosional Coasts) Picture!

Coastal Features (Erosional Coasts) What is the cause? Hydraulic Action Air is compressed in cracks by water moving in, may cause cracks to widen in rocks Wave Pounding Sheer energy of the wave hits the rock Abrasion/Corrasion Waves launch seaload at the cliffs Most effective/rapid form of coastal erosion – Attrition is when seaload is worn down by itself or a shoreline

Coastal Features (Erosional Coasts) Erosion causes (continued) Dissolution – Dissolving of rocks on shore by sea water – Can lead to caves – Corrosion is the dissolving of rock by carbonic acid in seawater Limestone cliffs are particularly vulnerable to corrosion

Coastal Features (Erosional Coasts) What happens to all of the eroded material? – Eroded Material is broken down into terrigenous sediment, then one of two things can occur: Transported by longshore drift to a depositional beach Stays at the home coast, and when enough sediment builds up a beach is formed. When will it stop? – Erosion continues until there is a beach large enough to stop waves before they hit the rocks

Coastal Features (Depositional Coasts) Mostly consist of build-ups of sediment Spit Extend in the direction of longshore drift. – Spits that continue to grow to the other side of the bay and completely cut off the bay from the open ocean are called bay- mouth bars, or bay barriers Stupid people build structures on bay barriers, which are not stable or permanent structures. (1m) Tombolo connect islands to either shore or another island.

Costal Features (Depositional coasts) Picture!

Coastal Features (Depositional Coasts) Barrier Islands. Very Important, and in need of a sophomore to do a power point on them. Here’s the basic idea: – They occur along depositional coastlines – Are long offshore deposits of sand that are parallel to shore Develop into their own ecosystems – My opinion: Great learning powerpoint

Coastal Features (depositional Coasts) Beach Compartments – Best comparison is describe a beach compartment as a cycle of sediment throughout an area. – Three main contributing factors: 1.Rivers supply sediment to coast 2.Sediment moving due to longshore transport 3.Sediment drained down into the ocean through submarine canyons – Beach Starvation Human structures, such as a dam, limit rivers, slowing depositing of sediment

Coastal Features (Depositional Coasts) Picture!

Coast Linearization Coast Linearization tells of the age of a coastline and how it has developed due to erosional and depositional factors. – Not boring like coastal features, actually pretty fun to learn about. – Is a convergence of all of the stuff you just learned about

Coast Linearization! The best example of coast linearization is the Mediterranean Sea. For Sophomores: The Mediterranean Sea dried up a long time ago, but then was refilled from the Atlantic. – When the Mediterranean first filled up with water, it had a lot of high- energy waves from the waterfall hitting it – Basicly, a new coastline. – We will follow what would ideally happen to this new coastline in the next few slides.

Coast Linearization When the waves first hit the rocks of the Mediterranean, an erosional coast was formed. – It was erosional in most areas – Irregularities in the rocks caused headlands and coves to form. At first, the coast becomes non-linear

Coast Linearization Important: Wave Refraction – Caused by uneven wave shoaling – Wave Refraction is the diversion of waves from coves, and the convergence of waves onto headlands. Effectively Creates a High-energy coast on the headlands Effectively creates a low-energy coast in coves Concept recall: what do low energy coasts do that high- energy coasts do not do? – ANSWER: they build a berm, or a beach Guess before you click! Did you guess right?

Coast Linearization

What’s going on now? – A beach is formed in coves that protect the rock their from erosion – Headlands have no protection and have waves being directed towards them because of wave refraction. – Headland decline is much much faster than the decline of coves at this point COOL ANIMATION: CLICK HERECLICK HERE

Coast Linearization Headlands retreat – Leave behind sea stacks and archs – The coast is straightened Sediment builds up, and the coast becomes depositional

Coast Linearization Overall concept: Most of the time, – A younger coast is erosional – An older coast is depositional

Emerging/Submerging Coastlines Two things can move coastlines. Surprise! Sea level changes. Land moves up and down as well. – Coasts that are rising above sea level are called emerging shorelines – Coasts that are sinking below sea level are called submerging shorelines

Emerging Coastlines Evidence is shown in: – Marine terraces – Stranded beach deposits – Evidence of sea life found above sea level – Sea caves above water level

Submerging Coastlines Drowned beaches Submerged dune topography Drowned river valleys

Emerging/Submerging Coastlines Mechanisms on land: Tectonic movements – Passive margins Moving away from a spreading center Usually submergent – Active margins Tectonically active Usually emergent

Emerging/Submerging Coastlines Isostatic Adjustment – Earth’s crust, especially continental crust, is floating. – Crust sinks when Crust sinks under accumulation of heavy loads of ice, vast piles of sediment, outpourings of lava – Crust rises when Heavy loads are removed – A very slow process

Emerging/Submerging Coastlines Eustatic changes in sea level – More ice = sea level lower – Less ice = sea level higher – Other Causes? Formation/destruction of inland lakes Changes in sea floor spreading rates – Faster spreading = raise sea level – Slower spreading = lower sea level – The slowest Thermal expansion of water – For every 1°C, sea level changes about 2 meters

Emerging/Submerging coastlines Link to ice ages – According to isostatic adjustment, continents sink under ice – However water level also raises when water melts from ice packs – Water also expands under heat – Which wins? Global warming raises sea level because thermal expansion and melting ice win.

Emerging/Submerging Coastlines Important word: Pleistocene – Estimated Sea level change to be 190 meters 120 below 70 above – Most Coastal Areas have evidence of both emergence and submergence – Most changes due to ice sheets forming/melting and taking/releasing water Thermal = 10m/5C

Emerging/Submerging Coastlines

Global warming – Increase in average ocean temperature of.6°C over the past 140 years – Eustatic sea level change of 4-10 in. up. – Global warming raises sea level.

Human Intervention Due to Eustatic sea level rise, 70% of sandy beaches are eroding 60% of humans live near the coast Rising sea level threatens human structures – we try to stop it

Human Intervention Hard Stabilization – Structures built by humans to stop beach erosion. Doesn’t work very well. – Groins and Jetties Built perpendicular to shore Groins create groin field Protect harbor entrances Both composed of large blocky material called rip-rap

Human Intervention

– Breakwater Built to create harbors free of waves create many problems, such as erosion downshore and unwanted tombolos. Dredging solves some of these issues Picture is very explanatory:

Human Intervention

– Seawalls Constructed parallel to shore Designed to stop erosion Very expensive

Human Intervention Alternatives to hard stabilization – Construction Restrictions Stop building of structures close to coastlines – Beach Replenishment/Beach Nourishment Sediment is added to a beach to stop erosion – Relocation Moving of structures

Human Intervention