UNIT 4: OCEANS AND SHORELINES STUDY GUIDE CHAPTERS: 9 AND 16 (Revised 7/16) UNIT 4 HOMEWORK worth 10 points WEB HIT HOMEWORK: Two written paragraphs, each with three complete sentences For any Unit Web Hits, go to the DMC HOME website; in Search box type Geology, select Vernon Kramer, scroll down to GEOL 1303, select Syllabus, select Web Hit Links, click on icon of interest for web sites OR: go to DMC Home website, select Degrees, Certificates, Courses, scroll down to Natural Sciences and select Geology, select Faculty Listings, select Walter Vernon Kramer, find Geol 1303, select Syllabus, and there you can find the web hit links click on icon of interest for web sites [IF NONE OF THE WEB SITES COME UP, YOUR COMPUTER PROBABLY NEEDS TO BE REBOOTED (RESTARTED) Oceans and Seawater - Oceans comprise 71% of the Earth s surface. - Oceans contain 97% - 98% of Earth s water. Statistics for Five Oceans - (In reality there is only one world ocean but geopolitics and environmental groups leads to the naming of five oceans.) Your very silence shows you agree Euripides 406 BC Earth s Five Oceans Ocean Area (square miles) Average Depth (ft) Deepest depth (ft) Pacific 64,186,000 15,215 Mariana Trench, 36,200 ft deep Atlantic 33,420,000 12,881 Puerto Rico Trench, 28,231 ft deep Indian 28,350,000 13,002 Java Trench, 25,344 ft deep Southern 7,848,300 13,100-16,400 ft Sandwich Trench, 23,736 ft Arctic 5,106,000 3,953 Eurasia Basin, 17,881 ft deep One s first step in wisdom is to question everything and one s last step is to come to terms with everything G. F. Lichtenberg Salt Content in Seawater - One cubic foot of average sea water contains 2.2 pounds of dissolved salts. - One cubic foot of fresh water generally has less than one ounce of dissolved salts. - There is an estimated 50 sextillion tons of salts dissolved in the oceans Salinity: a measure of dissolved salts of any type - Salinity (salts dissolved in water) is reported in ppt or parts per thousand; example would be the number of pounds of salt in 1,000 lbs. of water. - The average ocean salinity is 35 ppt (parts per thousands). 1
Salts in Seawater - Sea water, when evaporated, can produce minerals, including some of the following useful minerals: halite (table salt), gypsum (sheetrock), calcite (limestone rock), potash (fertilizer), and Epsom salts (laxative). Average Ocean Salinities - World-wide salinity is about 35 ppt, although the salinities can vary from 32-37 ppt for the open oceans and about 40 ppt for Red Sea. Coastal Bend Map review of local bays Concept Test Salinities of the Local Bays, (which have an environmental and financial impact upon us) - The GOM salinity varies from 28 36 ppt, depending upon periods of droughts or flooding. Most of the time, the salinity is below 35 ppt adjacent to the coastline. Estuary: any bay at the mouth of a river (like Nueces Bay and Copano Bay) - Copano Bay waters generally have a low salinity or brackish because of the Aransas and Mission Rivers. Brackish water: any water that has salinity between fresh water and sea water - Nueces Bay waters generally averages below ocean salinity or brackish. The Nueces Bay will become hypersaline without regular water releases from the upriver dams or during periods of droughts. Hypersaline water: above average seawater salinities (typical of the Laguna Madre) - Corpus Christi Bay averages near ocean salinity, principally because of the 50 deep ship channel. - Laguna Madre averages higher salinity or hypersaline, especially during periods of drought. This confined bay system averages less than 3 feet water depth (except where dredged deeper). Hydrological System include the Shorelines Subsystems - The majority of all humans live within 100 miles of an ocean or large lake. - All large bodies of water can dramatically affect people and shorelines. - FYI: Over the last century, it was thought that sea level had risen almost 5 inches (12 cm.) in some areas of the US, but the actual cause was a local sinking shoreline. 2
- Shorelines and coastal areas are often used interchangeably. Some consider shorelines as only areas in contact with a large body of water. Others consider coastal areas to include shorelines, islands, sand bars, etc. - Most shorelines are affected by wave action (erosion). Shorelines can affected by at least five (5) processes: 1. Waves 2. Currents 3. Tides 4. Sea level changes 5. Tectonics All men (and women) by nature desire to know - Aristotle Components of Waves - A water wave: is formed by transmitted energy or wind transferring energy to the water surface. The highest part of wave: Wave Crest The lowest part of wave: Wave Trough The elevation difference between the crest and trough of a wave: Wave Height - Wavelength is distance from crest to crest or from trough to trough of a wave. - Wave period is the timing between the passage of two crests or two troughs of waves. - The stronger the energy, the higher the wave height. - Wave motion of a particle of water is such that the water particle moves in a circular orbit. - Wave Base is the depth at which the wave energy diminishes to zero and that equals one half the wave length (see above for wave length) GUARANTEED EXAM QUESTION - What happens when the wave base hits the sea floor? The energy is forced upward and forward to make a breaker. The wave base hitting the sea floor can also make the sea water appear muddy. - The sketch above shows actual water movements within a deepwater wave and demonstrates the wave base. Drawing a wave base 3
The Beach and Waves Swash is the turbulent sheet of (wave) water that moves up the beach. Backwash is the (wave) water that flows back down the beach slope. Types of Breakers A breaker is defined as a collapsing wave and can be classified as five (5) types: - 1) Spilling Breakers; 2) Plunging Breakers, 3) Surging Breakers 4) Rogue Breakers or Rogue Waves; 5) Tsunami waves Spilling breaker is a wave that breaks on gentle sloping beach slopes. The wave is commonly seen as an advancing line of foam. This type of wave not only pushes sand up to the beach but also pushes sand along the beach. (Usually good for body surfing) Drawing a spilling breaker 2. Plunging breaker is a wall of water that collapses with a curl. These waves are more frequent in areas of steeper beach slope but also can be found associated with strong winds or longer period waves. (Usually good for using surfboards) Drawing plunging breaker 3. Surging breaker is a beach-destructive wave that surges up the beach face, usually as a wall of water. These waves are associated with high tides and storms or passing ships (sometimes called a storm surge wave). 4. Rogue waves are usually individual, extremely large waves that combine the fluid energy of many other waves. These waves are generally found near storms and can be very destructive and deadly. 5. TSUNAMI: A seismic (earthquake) sea wave. A tsunami is a long wave in the ocean caused by an earthquake, or a landslide on the seafloor. This will be discussed in greater detail with a later unit. - Wave erosion is powerful all round the Corpus Christi bay area where it creates bluffs, especially in the area surrounding Nueces Bay and Corpus Christ Bay and the barrier islands. Many local examples of shoreline destruction can be found. Facts do not cease to exist because they are ignored Aldous Huxley 4
Beach Sands - Gave a short presentation Offshore Currents Water current is a narrow linear river-like body of water that is continuously moving. - Currents can be created by: 1) Heat and the Earth s rotation (i.e. the Gulf Stream) 2) Wind currents, 3) Wave generated currents and 4) Tide generated currents Offshore currents are deep-water oceanic currents, mostly responding to energy from the sun, prevailing winds and the Earth s rotation (we will ignore most of these currents for now) Three Wave Generated Currents Found Near the Shore - As a breaker approaches the shore, the swash washes up on the beach (and for a moment this seawater is actually higher than sea level). Then the backwash returns the water back to the sea as a wave-generated current. -There are three different types of wave generated currents (surf zone currents) that include 1) longshore currents, 2) rip currents and 3) undertows. Longshore currents are generated because almost all the waves are pushing water up the beach and are hitting the shoreline obliquely. These longshore currents are found between the beach and the breakers and flows parallel to the beach or shore at speeds of 0.2 mph 4.0 mph. Eventually this water must get back into the sea. The seawater usually returns to the sea as a rip currents or rip tides. Rip current: A current (often called a rip tide or undertow) forms and exits when the longshore current encounters a gap in the sand bars (slough or trough) or a jetty. Here this potentially dangerous current moves perpendicular to the beach and back out to the sea at speeds of 4.0 mph to 9.0 mph. The geologic effect of rip currents is to remove sand (and swimmers) away from the adjacent beach. - The surface above the rip currents (often called undertow) is visible as small area of white foam going seaward. To escape a rip current, swim parallel to shore to exit the narrow, swift-moving current, and then swim to shore. - Surfers often use these rip currents to get a free ride back out to the surfing zone. You live and you learn or you don t live long Ernest Hemingway Picture of a rip current, showing how to escape by swimming parallel to the shore Undertows: Occurs when waves hit the shore perpendicular and the backwash returns back to the sea under the waves. They are considered dangerous for small children and when the waves are very high. (This is different than rip tides.) 5
Sand Moving on the Beaches - These three currents are always moving sand in the surf zones to different locations. One method is by longshore drift. Longshore drift refers to the process in which sediment is moved in a zigzag pattern along a beach. This drift or zig-zag pattern makes the beach a moving river of sand, along the water s edge to a new location. Tide Components Tide: periodic, short-term or daily changes in sea level along shoreline, generally caused by the gravitational forces of the sun and moon, as well as the Earth s rotation (astronomic tides). Ebb tide: outgoing tide Low tide: tide at its lowest level Flood tide: incoming tide High tide: tide at its highest level - A high tide and a low tide (Period) usually occur about 25 minutes later for the next tidal period. (Memorize this graph) FYI Frequency of a tide (generally two high and two low tides per day (50 minutes later each day) depends upon: 1. Irregularities of the shoreline 2. Variable coastal depth 3. Size and shape of ocean floor 4. Frequency of storms Tides and the Sun-Moon Alignments - Most tides are caused by the combined gravitational pull of the moon and sun and Earth s rotation. - The position of the moon strongly influences the types of tides. Spring Tides: biweekly intervals of higher (and lower) or maximal tide differences, caused when the sun, Earth, and moon are aligned. Stronger spring tides (i.e. daily higher and lower average sea levels) occur with the new moon when compared to a full moon. (Memorize this Spring tide graph (maximum tides)) 6
Neap Tides: biweekly intervals when the sun, the Earth and the moon form right angles. With these tides, the differences in water height between high and low tides are minimal (i.e. near average sea level). (Memorize this neap tide graph (minimum tides)) Frequency of Tides - Most of the bays of the Corpus Christi area have one high tide and one low tide a day; however, for various days throughout the month, the tides can vary from 2 tides a day to multiple tides a day. - Remember: tidal charts are predictions and vary from observed tides, especially during periods of strong winds. All truths are easy to understand once they have been discovered; the point is to discover them Galileo (Memorize this graph) - The up and down lines on the above graph shows daily high and low tide levels for at Corpus Christi for a two month period. - Notice at the neap tidal periods (quarter moon) there are very little differences between the high and low tide levels. - Notice that we also have stronger high-low tides during the spring new moon tidal periods compared to the spring full moon tidal period. 7
Concept Test Unusual Tides Proxigean Spring Tides are very high flood tides that occur for a few hours when the moon is closest to the Earth (new moon) within the proxigee phase (close to Earth) of its orbit. These tides occur once every 18 months. - Once every 31 years, when the Earth s elliptical orbit is closest to the sun, a phenomena known as an extreme Proxigean spring tide in which an extremely high and flooding tide for a few hours is created. - The most extreme daily tides occur at the Bay of Fundy (Canada). This bay has 65 feet tides twice every day; the incoming tide forms a wall of water called a tidal bore. Storm surge tides are destructive tides commonly found during large wind storms. Normal high tides can further increase the heights of storm surges, with destructive consequences. Flood Tide Deltas - We know that longshore currents push sands and sediments along the beach. When this sand is swept into the channel of a pass, the pass could fill up with this sand. However, strong currents associated with incoming tides can wash this channel-filling sediment into the adjoining bay, creating a flood tide delta: similar to that at Harbor Island, East of Port Aransas. (You drive on this when you travel from Aransas Pass to the ferries.) Education is a progressive discovery of our ignorance Will Durant Various Sea Levels - Sea level is not constant all over the Earth at any one time interval. Average sea level: that level between high tides and low tides Eustatic Sea Level: the global sea level; sea level rises when glaciers melt and sea levels fall when glaciers grow Other Factors Affecting Sea Level - Greenland has a large ice cap. If all of this ice were to melt, sea level would rise about 21 feet. - Local sea levels can be affected by rising or sinking land levels or by severe erosion. Different types of Coasts - Most of the GOM is a passive margin coast, because it is not along a convergent zone. This results in a flat, featureless surface, extending from the continental interior to the edge of the shelf. Minor sea level changes along the GOM (passive margin coast) will have major impacts on the coast.(see below) A passive coast 8
- A convergent zone (subduction zone) produces a convergent coast. The subducting plate is pushing the coastal land up, to form mountains. In general this means steep-sloping beaches and shorelines with rocky cliffs. This will result in big, destructive (plunging) waves being common. Rising sea level has less impact here. (see below) A convergent coast Blowholes - Waves can undercut rock cliffs. Incoming waves can trap and compress air here and create a unique feature called a blowhole. These blowholes can force water to almost 50 feet in height, into the air. A video of the Dragon blowholes of Hawaii was shown. 9
SAFETY RULES 1. WEAR A LIFEJACKET IF YOU DON T SWIM WELL. You buckle up in your car, so should your children buckle up their lifejacket when they swim in the surf. A lifejacket will SAVE YOUR LIFE, it is nearly impossible to drown if you are wearing a Coast Guard Approved Life Jacket. I have had the unpleasant task of pulling many lifeless bodies from the surf, all of them would be alive today if they had been wearing lifejackets. 2. LEARN TO SWIM 3. BE AWARE OF RIP CURRENTS 4. OBEY WARNING SIGNS AND FLAGS 5. HAVE AN ADULT CHECK CONDITIONS FIRST 6. DON'T SWIM ALONE 7. STAY IN WAIST DEEP WATER DURING HIGH SURF 8. NEVER LEAVE CHILDREN UNATTENDED 9. DO NOT SWIM NEAR THE JETTY 10. DON'T USE INFLATABLES IN THE SURF 11. DON'T OVERESTIMATE YOUR SWIMMING ABILITY 12. DON'T DRINK AND SWIM Rip Currents Rip currents (mistakenly called rip tides or undertows) are common and can be found almost daily on all South Padre Island Beaches. RIP CURRENTS KILL SWIMMERS EVERY YEAR HERE AT SOUTH PADRE ISLAND. Rip currents occur around the world at "surf" beaches, including both the Atlantic and Pacific coasts, the Great Lakes, and the Gulf of Mexico including South Padre Island. Rip currents are also the #1 cause of drowning. If you are caught in one, how you respond could make the difference between life and death. Unlike undertows, rip currents are shallow water processes that do not pull a person under. They form when water, piled against the shore, begins to return to deeper water. Typically, strong wind and swell waves push water over a sandbar allowing excess water to collect. Eventually, the excess water starts to return seaward through low areas in the sandbar, "ripping" an opening. Rip currents can be readily seen from the shore. You can spot a rip current by looking for objects or foam moving steadily seaward. Wave heights are also lower and choppier in rip currents. Since rip currents are NOT undertows, you can be pulled away from the shore but not pulled under the water. The most common mistake drowning victims make is to panic and try to swim directly toward the shore. Even the best Olympic swimmers are not able to successfully swim toward shore in the strongest rip currents. If caught in a rip current, simply remain calm and swim or paddle to the side and the surf will push you back towards shore. Do not hesitate to call for assistance. Rip Currents are common, be aware! 10