Beaches and Coastal Environment
What is the difference between weather and climate?
Weather- the state of the atmosphere in a given area over short time periods (hours, days, weeks). Climate- statistical patterns & trends that describe the state of the atmosphere in a given area over long periods of time (months, years, decades, centuries, millennia).
Where would you expect to find water particles moving in an orbital path below the surface of the ocean? Where would that orbital motion path become elongated and transition to an elliptical path. Why does this occur?
in the open ocean, water particles travel in an orbital path. When waves begin to "feel" the bottom it reduces the forward speed, causing friction. The orbital motion transitions to an elliptical path & then just oscillates back and forth.
Please describe the process of wave shoaling.
Wave crest are more closely spaced in the nearshore and faster deep water waves also tend to catch up to slower shallow-water waves as part of shoaling (Wavelength decreases, height increases)
In class we were given the general form of the wave speed equation as C=L/T. However, we also learned that actual waves in the ocean don't conform to surface wave theory and that the universal wave speed equation (any water depth) is actually a bit more complicated than that. We then discussed the differences in wave speed equation for both deep and shallow water waves. Based on these equations, which fundamental characteristic determines wave speed in deep water? In shallow water?
Wave speed depends upon the wavelength in deep water. Wave speed is determined by water depth in shallow water.
What makes waves and what factors determine wave size in the ocean? Are waves the same in deep and shallow water? Why or why not?
Waves created by wind, tectonic movement, sun and moon, etc. Wave size determine by wind speed, length of time wind blows, and fetch (distance wind has blown over ocean surface) Waves get larger as they move to the shore, because the bottom of the waves piles up when it has no where to go down (bottoms out). The wavelength shortens and the wave height heightens.
Please define and differentiate between the processes of weathering and erosion.
Weathering- the physical breakdown & chemical decomposition of rock in place Erosion- the physical removal of weathered material (sediments) by wind, water, or ice
What are Milankovitch Cycles and how have they influenced Earth's climate and sea level over at least the last 2 million years or so?
eccentricity: orbit around the sun obliquity: axial tilt precession: axial wobble Milankovitch Cycles-changes in solar radiation Glacial-interglacial cycles caused by these variations in Earth's orbit
Please list the classification of grain sizes from largest to smallest.
gravel, sand, silt, clay
Please discuss the geologic concept of isostasy and how it can lead to subsidence or uplift by changing ice volume on a continent.
isostasy is the concept of floating crust in gravitational balance. add weight & crust subsides remove weight & crust rebounds sediment deposition & erosion glacier formation & melting
When waves refract along an irregular shoreline, where does most of the wave energy get concentrated? What are some common features produced along rocky coasts when this happens?
over time, wave erosion straightens an irregular shoreline. most of the wave energy is concentrated against the sides & ends of headlands, leading to the formation of caves, arches, stacks, & stumps.
Yes, and what was the geochemical proxy that is used to infer temperature changes and ice volume over the last 2 million years or so...
oxygen isotope proxy: records isotopic changes of seawater @ the time of shell formation decrease temperature, ratio increases (more ice) increase temperature, ratio decreases (less ice)
Please define and differentiate between the terms coast, coastline, shore, and shoreline
Coast- extends inland from the shore as far as ocean-related features (bays, tidal, creeks) are found. Coastline- marks the seaward edge of the coast. Shore- area between the lowest tide level & the highest elevation on land that is affected by storm waves. Shoreline- line that marks contact between land & sea (changes w/ tides).
Please define and differentiate between continental shelf, continental slope, and continental rise.
Continental shelf- vary greatly in width; gently sloping, flooded extensions of the continent; contains important mineral deposits; some areas are rimmed by extensive glacial deposits Continental slope- steep sloping structure between continental rise & continental shelf; marks the boundary between continental crust & oceanic crust. Continental rise- gradual incline rising up from the flat, deep ocean floor; found in regions where trenches are absent; turbidity currents deposit thick accumulations of sediment that form deep-sea fans.
What are the primary and secondary factors that drive plate tectonics, and what is the process that splits continents and forms divergent margins and new ocean basins?
Convective flow in the mantel is the basic driving force of plate tectonics. Other forces that drive plate motion: Slab pull (density), Ridge push (gravity), Drag (friction). Divergent plate boundaries in the middle of continents result in continental rifting. This splits landmasses into two it more smaller segments along a continental rift zone, often creating new coastline.
Please identify and define some of the basic measurements we can use to describe waves. Think both measures of distance and time, as well as parts of a wave, when developing your answer.
Crest - top of the wave Trough - low area between wave crest Wave height - the overall vertical height between the wave crest and the wave trough Wave Length - the distance between two like locations on the wave form: crest-to-crest or trough-to-trough Steepness - ratio of wave height to wave length (H/L) Period - time interval required for a wavelength to pass Frequency - number of wavelength passing per second
In class we discussed 3 major types of plate boundaries. Which type of boundary is characterized by mid-ocean ridges where new oceanic crust is formed? Which type of boundary results in the loss of old, dense crustal material? Which type of boundary neither creates nor destroys crustal material?
Divergent plate boundaries (constructive margins): most are located along the crests of mid-ocean ridges Convergent plate boundaries (destructive margins): in most cases, this is where older portions of oceanic crust are returned to the mantle Transform fault boundaries (conservative margins): plates can slide past one another w/ no new lithosphere being created or destroyed
Please describe the process(es) that leads to the formation of volcanic island chain in the middle of an oceanic plate (i.e. away from active margins of the plate). How is this similar or different than the process(es) that lead to the formation of volcanic island arc along an active margin?
Hot Spots: Caused by rising mantle plumes of magma Volcanoes form & are active only over the hot spot. As the tectonic plate moves over the hot spot, more volcanic islands are created forming an island chain (Hawaiian Island Chain). Differences: A hot spot creates, and only has, one active volcano at a time while an active margin can create & support multiple active volcanoes at once.
What is the Inman and Nordstrom Tectonic Coastal Classification Model, and how does it classify and differentiate different types of coasts?
Inman and Nordstrom Tectonic Coastal Classification Model considers continental shelf and uplands bordering the coast on 1000 km scale. Its classification is based primarily on tectonic setting. Secondary factors includes: other side if continent, age of coast, exposure to open ocean, and climate. Types of coasts: Collision Coasts Continental Island Arc Trailing Edge Coasts Neo-trailing edge Afro-trailing edge Amero-trailing edge Marginal Sea Coasts
Please describe how eustatic sea level has changed since the last interglacial (125,000 ybp). What were climate and sea-level conditions like then? How were these conditions different during the last ice age (last glacial maximum, ~18,000 ypb). How is sea level projected to change in the future and what are some realistic best case and worst case scenarios for Florida over the next 85 years or so?
Last interglacial period: Seas 4-6m higher, temperature 1-2 degrees warmer than present Last glacial maximum: Seas 100m higher, 2-3 degrees cooler than present Next 85 years in FL: 0.7-1.8m (3.22mm/yr) by 2100 (current projection)
How many major lithospheric plates are currently found at Earth's surface?
Lithosphere consists of seven major plates.
The longshore current and beach drift are fundamental coastal phenomena that have major control on the shape and evolution of coastal environments. What fundamental processes cause the longshore current and beach drift, and how do these coastal processes change when man-made structures are introduced along the shore?
Longshore currents (parallel to shore) cause the beach to erode and drift off down the beach. Longshore currents are caused by the waves coming towards the beach shore and moving back out to the ocean. Beach drift-sediment moves in zigzag pattern When man-made structures are placed along the beach they disrupt the flow of the sand and cause pile ups and odd patterns.
Where is new oceanic crust formed? where is it destroyed?
New oceanic crust is formed at mid-ocean ridges. The older, cooler, and denser slabs of oceanic lithosphere descend into the mantle at subduction zones.
What are proxy records and how are they applied to our understanding of Earth's climate and sea-level history?
Proxy records: any observable/measurable marker used to indirectly understand a past condition on earth Common sea-level proxies: wave-cut features (cliffs/notches) salt marsh & mangrove peats coral & oyster reefs past shorelines can either be submerged below or elevated above modern sea level
Please define and differentiate between the terms wave refraction, wave reflection, and wave diffraction.
Refraction: bending of wave Reflection: wave encounters barrier, reflected at same angle approached as Diffraction: response of wave to impermeable obstacle (rock, barrier), crest partially stopped
Was the theory of plate tectonics immediately accepted by the scientific community and public at-large? Describe some of the hypotheses/events/scientific developments that led to the development of the theory of plate tectonics.
No, there were many objections including: lack of a mechanism for moving continents; Wegener incorrectly suggested that continents broke through the ocean crust; strong opposition to the hypothesis from all areas of the scientific community. Alfred Wegener 1st proposed the continental drift hypothesis in 1915. Started as the super continent called Pangaea, and continents "drifted" to present positions. This hypothesis was correct in principle, but had some incorrect details... Harry Hess' sea-floor spreading hypothesis: discovery of matching magnetic stripes in the oceanic crust on both sides of mid-ocean ridges. Paleomagnetism & geomagnetic reversals were the most convincing evidence provided to support the continental drift & sea-floor spreading hypotheses
What is the difference between an active and passive continental margin? What types of features are associated with each?
Passive: not next to plate boundaries, ex. Atlantic coast Active: tectonically active regions, narrow cont. shelf, steep slope, usually trench. ex. Pacific coast
Please define and differentiate between the terms sorting and rounding in a sedimentary context.
Sorting-degree of similarity in size: well sorted (transported far from source/distributed long time ago), poorly sorted (close to source/rapid distribution) Roundness-well rounded (a lot of erosion/abrasion over long time), very angular (short distance over short time)
Please describe how sedimentary characteristics of beach sands can tell you about the source of the sediments, distance they have traveled, and energetics of the depositional environment.
Texture: Fine mud-low energy (no waves/currents), ex. deltas, bays, Ft. De Soto Sand-medium energy (waves, winds, currents), ex. beaches, dunes, tidal inlets, St. Pete Beach Gravel-high energy (big waves, high winds, fast currents), ex. rocky coasts, East Coast, California Source/Composition: Muddy-clays, organic muds Sand-quartz, some feldspar (land) Pacific Islands-basalt (black), coral debris (ocean floors) Bahamas-calcium carbonate (coral/organism shells)
Waves in the ocean rarely perfectly conform to surface wave theory, instead there are many numerous complicating factors that can change the characteristics of a wave. Please consider what happen when a wave encounters a surface current moving in the same direction as the wave. What will happen to the wave when it encounters such a current?
The wavelength of the wave will increase while the wave height decreases.
What are turbidity currents and what type of sedimentary feature do they produce?
Turbidity currents-downslope movement of dense sediment laden water excavate sand & mud from shelf & slope graded beds
What type of coastal environments are associated with depositional coasts? erosional coasts?
Erosional Coasts: Beaches Rocky coasts Depositional Coasts: Beaches Deltas Barrier Islands Reefs Glaciated coasts
Please define and differentiate between eustatic sea level and relative sea level.
Eustatic Sea Level- global change in sea level due to a change in ocean volume (temperature) or basin size (tectonics) Relative Sea Level- average height of the ocean relative to the local land surface (benchmark)