Aerial image is taken of Chatham with Pleasant Bay visible, along with parts of Orleans in the background.
Pleasant Bay is located on the Cape Cod, defined as the farthest section near the "Elbow."
Cape Cod was formed from the Laurentide Ice Sheet's retreat, leading to the deposition of sandy material, creating sandy land formations distinct from the granite coastline found in areas like Maine.
Coastal Features
Discussion centers on various coastal features such as:
Barrier beaches
Spits
Bay mouths
These features emerge from processes where sand is transported by wave action, winds, and river sediment distribution.
Waves cause movement of sediments that lead to the formation of barrier beaches, impacting the hydrodynamics and water quality of adjacent estuaries like Pleasant Bay.
Estuaries and Water Quality
Study of estuaries often focuses on nitrogen as a key pollutant, which enhances phytoplankton growth.
Seasonal cottages originally built on septic systems contribute to nitrogen leaching into groundwater, affecting estuary health.
Pleasant Bay serves as both an estuary and as an example of how increased exchange between estuarine and ocean waters can improve water quality ("dilution is the solution").
Changes in barrier configurations can significantly impact hydrodynamics and, consequently, water quality; e.g., breaks in barriers allow for more clean water influx.
Effects on Marine Life and Human Activity
Water quality influences the growth of seagrass, which serves as nurseries for fish.
The growth and health of oysters are also contingent upon water quality, affecting commercial practices due to possible closures.
Coastal Dynamics
The term "coast" includes all areas influenced by ocean processes.
Coastal climate influenced by cycles such as:
Land breezes
Day-night cycles
Seasonal cycles influenced by monsoon effects
Erosion along the coast is primarily driven by wave action.
Coastal regions can extend up to tens of kilometers inland.
Modern coasts have fluctuated due to sea level changes between six to 125 meters over the past two million years.
Coastal morphology, such as Pleasant Bay, is shaped by wave action, sediment supply, and sea level changes.
Beach Nourishment and Marshes
Many beaches require additional sand to be brought in due to natural erosion.
Marshes also need sediment to maintain elevation and survive sea level rise.
Beach Composition and Formation
Beach sand composition varies based on local geology and sediment sources:
Tropical white sands typically come from coral breakdown
Quartz sands, prevalent in local areas, originate from continental sources.
Beaches devoid of fine sand (mostly pebbles) indicate high-energy zones because lighter particles are washed away.
Black sand from volcanic activity can be found in places like Hawaii and Iceland.
Grain size indicates wave energy; finer sandy beaches correlate with low-energy waves, while coarser sands indicate high-energy conditions.
Anatomy of a Beach
The anatomy includes:
Back shore: region above high tide, affected during storms or king tides
Foreshore: intertidal zone between high tide and low tide
Near shore: extends to wave base
Offshore: beyond wave influence
Features include swash zone (onshore water movement) and backwash (offshore water retreat).
Longshore bars form from sand movement off beaches, affecting wave dynamics.
Different zones reflect beach activity depending on location and seasonal changes.
Wave Dynamics (Swash and Backwash)
Swash: onshore movement of water driven by breaking waves, generally results in deposition.
Backwash: the retreating water that carries sand back offshore.
Depending on energy conditions, either swash or backwash may dominate; low-energy environments favor sand deposition, while high-energy settings encourage sand removal.
Longshore Currents and Transport
When waves approach at angles, they induce longshore currents that result in the net movement of sediments along the shore, creating a current that can travel at speeds up to four kilometers per hour.
This transport is notable in settings where consistent wave direction dictates sediment movement.
Barrier beaches like those in Pleasant Bay are shaped by these currents, adding complexity to coastal sediment dynamics.
Rip Currents
Definition: a strong current typically found between sandbars that allows water moving onshore to return seaward.
Safety Tips
If caught in a rip current, swim parallel to shore.
Alternatively, keep afloat and allow the current to carry you back to calmer waters.
Erosional vs. Depositional Coasts
Erosional Coasts
Characterized by high energy and predominantly found in tectonically active regions (e.g. Pacific coast).
Formed through wave action; these coasts are marked by features like headlands, sea cliffs, coastal caves, and stacks.
Depositional Coasts
Found on passive margins like the Atlantic; they are low energy and defined by sediment accumulation.
Often shaped by river dynamics, creating deltas and beaches formed from sediment deposits.
Spits and Bay Mouth Bars
Spits are elongated deposits of sand extending from the mainland into open water, formed by longshore currents.
Bay mouth bars are similar in composition but span across the mouth of a bay, potentially affecting floodplain exchanges with the ocean.
Barrier Islands and Coastal Geomorphology
Barrier islands are formed from sediment deposition, typically found along the Atlantic and Gulf of Mexico coasts.
They provide distinctive features: ocean beaches, dunes, lagoons, and flats.
These are dynamic structures, vulnerable to erosion and natural transport processes.
Vegetation such as dune grass plays a critical role in stabilizing these sandy environments.
Conclusion
Observations of Pleasant Bay point to the dynamic interaction of natural processes that create and sustain coastal environments.
The continuous movement of sand, sediment transport, and water exchange due to these processes are crucial for maintaining ecological balance and the economic health of nearby regions.
Tools like Google Earth can visualize these coastal changes over time and highlight human impacts on these natural processes.