Chapter - Oceans and Coasts

Transcription

1 Chapter - Oceans and Coasts Discussion: What do oceans contribute to the environment of Earth? How do Earth s major systems relate to the oceans?

2 Oceans and Coasts Oceans are important - Thermal regulation of the Earth - controlling climate - source of food - source of mineral resources - source of energy - in constant flux- changes all the time - People live near and utilize oceans

3 Oceans relate to all 5 spheres of influence in many ways. Here s a few... Exosphere - The tides in the oceans are created by the gravitational pull of the moon and sun Biosphere - many organisms live in the oceans and those that live on land along coasts are subject to modification of coastal environments by oceans Geosphere - oceans erode and re-deposit large amounts of sediment from the geosphere Atmosphere - the oceans provide water for evaporation into the air and the start of the hydrologic cycle Hydrosphere - oceans are the main part of the hydrosphere, making up 97% of all water on the Earth

4 Some Characteristics of oceans Characteristics > Covers 3/4 ~ 75% (75%) of the of the surface surface of the of the Earth planet > Ocean water is salty, and cannot be consumed! - Salt content was used to try and estimate the age of the Earth -> > Primary component of the hydrosphere & the Hydrological cycle The hydrologic cycle

5 Thermal energy redistribution & moderation Oceans help control Earth s climate

6 La Niña - see the cool water off northwestern South America

7 El Niño - see the warm water off northwestern South America

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9 Air masses & where they form- this is important! Many airmasses are affected by the oceans mp, MT (red circles) control temps and moisture. In return, they air masses affect the ocean circulation - ca = continental Arctic > very cold & dry - cp = continental Polar > cold and dry - mp= maritime Polar > cool and humid - mt = maritime Tropical > warm and humid - ct = continental Tropical > warm and dry m = maritime - means over an ocean and is moisture laden (wet) c = continental- means over land and is dry T = Tropical - means air is warm P = Polar - means air is cool Red circles are influenced by oceans

10 Parts of the ocean basin Active Passive Most linked to plate tectonic activity

11 trenches sea mounts (guyots) ridges mid ocean ridge continental shelf abyssal plain

12 Which of the following is not something that influences erosion and deposition along coasts? A. Waves generated by wind B. Tides generated by the sun and moon s gravity C. Large scale gyres D. Currents generated by waves interacting with the coast E. All of the above influence coasts

13 Wind generated Waves waves Waves - oscillations of the water surface. Agents of erosion, deposition & transmit energy Crests > high points on a wave, troughs are low points. Wave length > the horizontal distance between successive wave crests or troughs. Wave height > the vertical distance from crest to trough. Factors influencing coastal areas (1)

14 Wave orbits movie

15 Waves and Terminology Applied Waves and Terminology Applied Point at which water starts to move toward beach Area outlined in red was shown in the previous slide...

16 Wave Generation Usually caused by wind blowing across the surface of the water. Can be caused by seismic activity too Can be caused by seismic activity > e.g., Tsunamis > Tsunamis Wind generated waves are influenced by Velocity of wind (windspeed) Duration of wind (time) Distance over which the wind blows. > known as Fetch. Slope of sea floor influences how the waves will break

17 Breakers form when wave crest advances faster than wave bottom. spilling breaker Surging waves, spilling waves and curls or tubes are the three types of breaking wave forms

18 Curl or tube breaker

19 Surging breaker

20 Large Scale Currents or Gyres Factors influencing coastal areas (2)

21 Ocean conveyor belt moves water and heat Ocean conveyor belt movie

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23 Nearshore Currents Nearshore > the area from shore to where waves break. 2 types of currents are important in coastal modification: > longshore currents > rip currents. Refraction & Longshore Currents Waves approach the shoreline at an angle (i.e. not perpendicular). Waves appear to bend becoming nearly parallel to shoreline > called wave refraction.

24 Nearshore Longshore Currents- Currents Longshore direction of longshore current form when the flow of water is not perpendicular to the shore, Causing a current to flow in the general direction of wave movement.

25 Rip Currents Nearshore Currents- Rip Water can't continue to pile up on shore eventually, it accumulates and gathers into a strong, perpendicular to shore, offshore current > called a Rip Current Often current erodes a small submarine channel

26 Rip Currents are narrow surface currents that flow out to sea through the breaker zone

27 Rip currents

28 Tides are regular fluctuations of the sea's surface in response to the gravitational pull of the sun and moon. Sun s 's pull is is less than Moon's because it's farther away away F grav = G*(mass1 x mass2) distance 2 2 high tides and 2 low tides occur daily in most areas. Factors influencing coastal areas (3)

29 Tidal types Rising tides (aka "flood tide") create a flood current > water flows toward land Falling tides (aka "ebb tide") create an ebb current > water flows away from land Spring Tides are higher than normal tidal ranges Neap tides are lower than normal tidal ranges

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32 Types of Coasts (2:2) Classification of Coasts Emergent- tectonically active > tend to be mostly erosional > sea-level fall or land-level rise > small bays, rocky coastlines Submergent- tectonically inactive > tend to be depositional > sea-level rise or land-level fall > large bays, estuaries, barrier islands, lagoons

33 Submergent coasts - caused by - sea-level rise - land subsidence. East &Gulf Coasts of the US classify as Submergent Coasts Submergent Coasts Chesapeake Bay is a classic example of Estuary (drowned river valley).

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35 Shoreline Deposition Depositional features include deltas, beaches, spits, baymouth bars, and barrier islands. Beaches are continually modified by waves and longshore currents. Spits and baymouth bars form from deposition by longshore currents.

36 Definition The beach A beach is a deposit of unconsolidated sediment extending landward from low tide to a change of topography such as sand dunes, a sea cliff or permanent vegetation.

37 consist of a long narrow strip of unconsolidated sediment (sand) and constantly change. They may be long continuous beaches or small pocket beaches.

38 Emergent Coasts Emergent coasts are found where land has risen relative to sea-level. This often occurs in tectonically active regions (orogeny or isostasy) Western US coast, northeastern Canada and Scandinavia are examples.

39 Sea Arch

40 Sea stacks and wave cut platform at low tide

41 Wave-cut Platforms and Associated Landforms Sea cliffs retreat, forming a beveled surface known as a wave-cut platform. Location: Hawaii

42 Rising Sea Level and Coastal Management Most US shorelines are eroding, some severely. y y

43 Groins

44 Breakwater Deposition occurs behind the breakwater wall, with erosion on either side it.

45 Storm erosion

46 Before After

47 Before After

48 Before After

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50 Deltas A landform formed by rivers transporting and depositing material in the ocean - subsequently modified by tides, waves, and human interactions Mississippi River- river dominated delta

51 Nile River- wave dominated delta Ganges-Brahmaputra River- tide dominated delta