Wave Action Laboratory Exercise

ESC 210


The following landforms are from Puget Sound, but the types of features shown are representative of those found along many shorelines.



















Shore Forms  

A gallery of beach shapes can be found along Puget Sound. As waves sweep materials along the shore, beaches form where sediments collect. Eroding bluffs often provide building materials for shore forms. Rivers and streams may also add sediments. Waves and currents sort these materials, and deposit them on a bar, spit, cuspate foreland, tombolo, or beach.

Dungeness Spit, Clallam County.


A double tombolo, Decatur Head, Decatur Island, San Juan Islands.

Shore Forms: A Gallery

·  Spit
A spit is a strip of beach which extends into deeper water. Most spits along Puget Sound straighten a curving shoreline. Spits often form a straight ridge of sediment across a bay. Spits commonly develop in the direction of shore drift.  

Some spits jut out from the mainland like an arm. Dungeness Spit, a large arm with complex barbs and hooks, is one on the largest natural spits in the world.  

·  Tombolo
Tombolo, an Italian term, is a spit or bar connecting an island to the mainland. Tombolos form in areas protected by large waves. The sediments to make a tombolo can come from the mainland beach or the island. A single tombolo is a single ridge connecting to an island.  

·  Double Tombolo
A double tombolo has two ridges extending to shore. Double tombolos can form in areas where there is a seasonal shift in shore drift.  

·  Cuspate Foreland
Cuspate forelands are triangular points or capes made from sediment deposits. Along Puget Sound, forelands can stretch from a few acres to a few miles. In many cases, forelands are created when two shore drift directions meet.  

·  Bar
Bars are ridges of sand seen when tides are low. Bars can be unstable, shifting with storms and seasons. During storms, bars can break the force of big waves.  

·  Looped Bar
Wind and waves have curved this finger of land into a loop. Looped bars often shelter a small lagoon, bay, or marsh.  

·  Delta
Deltas form where streams and rivers deposit sediments faster than waves can remove them. An array of deltas can be found along Puget Sound.




Cape Cod
National Seashore


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Cape Cod resembles a flexed arm of sand thrust out into the Atlantic Ocean. It owes its origin to glaciers, which were active in the area as recently as 14,000 years ago. Since that time, waves and nearshore currents have extensively reshaped the sedimentary deposits left by these glaciers into a variety of coastal environments, for example, sandy beaches flanked by towering sea cliffs and bluffs and discontinuous chains of barrier islands, many with elegantly curved sand spits. Remarkably, the 40-mile-long eastern coastline of Cape Cod, despite its proximity to Boston, possesses few shore-protection structures; it is the longest, pristine shoreline of sand in New England (Pinet, 1992).

About 15,300 years ago, a huge ice sheet, which flowed southward from Canada, covered all of New England. As the ice mass crept across the continental shelf, one of its ice lobes—the Cape Cod Bay Lobe—deposited sediment at its margin and formed a morainal ridge—the terminal moraine—that can now be traced across Martha’s Vineyard and Nantucket, the two principal islands south of the Cape. In addition to the terminal moraine, recessional moraines also indicate the presence of the former ice sheet in southeastern Massachusetts. As the ice sheet retreated northward, meltwater trapped by the recessional moraine formed Glacial Lake Cape Cod. Stratified muds, silts, and deltaic sands accumulated in this glacial lake, which covered an area amounting to about 400 square miles. A river outlet cutting into the recessional moraine drained water out of the lake, presumably in the area of Eastham and Town Cove section of Nauset Beach. The South Channel lobe was just to the east, and its meltwater carried huge quantities of sediment from the glacier. This sediment formed the gently sloping (towards the west) outwash plains that are several miles long and now comprise much of the Outer Cape.

When the ice sheet disappeared, the landforms of the Cape looked quite different than they do today. As the ice melted, sea level rose and flooded the area. Paleogeographic reconstructions of the shoreline indicate it was quite irregular at that time—a series of headlands and embayments composed of unconsolidated glacial sediments (glacial drift). This original coastline was located as much as three miles seaward of the present shoreline. Since then, sediment redistribution by waves and nearshore currents has changed the morphology of the landforms.

Landscapes change quickly in Cape Cod, and the retreat of the ice sheet is no exception, taking less than 3,000 years. Likewise, the creation of landforms after glacial retreat happened quickly, some taking as little as several hundred years. Outwash plain deposits, which are commonly pocked and pitted by kettle holes (e.g., the Wellfleet pitted outwash plain), are the major geologic feature of the lower Cape. When the kettles are deep enough to intersect the water table, a pond is formed. Pond level provides a close approximation of groundwater level.

The encroachment of the sea following deglaciation permitted wave currents to erode and rework the glacial drift. As waves refracted, energy was focused on the headlands. Consequently, peaks of land were worn down by wave erosion, creating a system of steep, wave-cut cliffs. The sediment moved by nearshore currents sequentially formed a series of sand spits and barrier islands (Uchupi et al., 1996). Prior to 6,000 years ago, the longshore drift of sand was predominantly to the south. This prevailing pattern of sediment movement formed the southern barrier island system of Nauset Spit, and eventually, Monomoy Island. The crest of Georges Bank, far offshore, still stood above sea level and afforded the northern shoreline of the Cape protection from erosion by large ocean waves approaching from the southeast. About 6,000 years ago, however, the rising sea submerged Georges Bank, exposing the Cape to wave attack from the southeast, resulting in the northerly transport of sand that eventually formed the curved spit system of Province Lands surrounding Provincetown. The appearance of the spit sheltered the northern shoreline and resulted in a northward transport direction on the bayside, whereas further south littoral transport was directed southward along Cape Cod Bay.

Erosion of the glacial deposits produced imposing marine cliffs, many of which are currently retreating at alarming rates. Although scarp retreat of the eastern shoreline averages 0.67 m/yr, specific coastal sites are losing land to the sea at higher rates. For example, the cliffs below Wellfleet-by-the-Sea are retreating approximately 1.0 m/yr (Pinet, 1992). Because most of this erosion occurs during storm events, cliff retreat is not constant over time.

A summary of Cape Cod’s geology is not complete without mention of sand dunes. This feature epitomizes Cape Cod itself—migrating constantly yet somehow enduring. Dunes are shaped by the prevailing winds and migrate constantly. On the Provincetown spit, there are parabolic dunes, or “U” shaped dunes, with the open end facing the wind. These are formed when the wind blows away the sand in the middle of the dune, exposing the underlying beach deposits. The eroded sand is transported by the wind and deposited along the advancing leeward face of the dunes (Oldale, 1998). The parabolic dune orientation is driven by strong winds from the northwest predominantly in the winter, but occasionally important in the summer (Allen et al., 2001).

Active coastal dunes are dynamic landforms whose shape and location are ever-changing. Youthful, unvegetated dunes are on the move as the sand, exposed to the prevailing wind, is picked up, transported, and redeposited repeatedly. When the dunes become vegetated, they stabilize and tend to remain unchanged for a time. If the dunes lose the protective vegetation, they will move again. This can be seen along US Route 6 in Provincetown, where once stable dunes are advancing on the forest and highway and are filling Pilgrim Lake (Oldale, 1998).


1. Cape Cod Topographic Map: 1:250,000 app. 4 miles per inch B & W copy and  Provincetown 1:24,000 topographic map.

1. To what does Cape Cod owe its origin? Continental Glaciers

2. What have waves and nearshore currents done to the glacial deposits? Reshaped them into sandy beaches, towering sea cliffs and bluffs, a discontinuous chains of barrier islands, and elegantly curved sand spits.

3. How prominent are man-made shoreline protection structures? Not prominent, very few.

4. Where can you find the terminal moraine from the Cape Cod Bay Lobe? South of Cape Cod in Nantucket Island and Martha's Vineyard.

5. What types of glacial materials resulted from the Cape Cod Bay Lobe? Till, Lacustrine, Outwash

6. a. What glacial feature represents the major geologic feature of the lower Cape? Wellfleet pitted outwash plain.

    b. How common are kettle lakes and ponds on the southern arm of Cape Cod? (See map from which your B & W copy was made to make it easier to answer the question.) Very common. The E-W arm of Cape Cod is an excellent example of a pitted outwash plain.

7. What features did a predominantly southerly longshore drift produce? Nauset Spit, (beach) and Monomoy Island

8. a. What happened when Georges Bank was submerged? The Cape was attack by waves from the southeast.

   b. What did the northerly transport of sand accomplish? Formed the curved spit system that surrounds Provincetown.

9. a. What direction of current movement is indicated by Long Point? (More easily seen on Provincetown 1:24,000 map.) Northeastward

    b. What direction of current (littoral) movement is indicated by Jeremy Point? (See on B & W 1:250,000 map.) Southward.

10. a. Which type of dune is found on the Provincetown spit? Parabolic

      b. What is the shape of this type of dune? U shaped, Horseshoe shaped

      c. What wind direction is most responsible for the orientation of the dunes? Northwest

      d. What causes the dunes to stabilize or migrate (move)? Establishment of vegetation will stabilize the dune and destruction of the vegetation will cause the dune to migrate.

Read the following section on Barrier Islands as this is what you will be seeing at Cape Hatteras, N.C. and Cape Canaveral, FL

What are Barrier Islands?

Photo courtesy USGS
Barrier island or spit

Barrier islands are long, narrow, offshore deposits of sand or sediments that parallel the coast line. Some barrier islands can extend for 100 miles (160 km) or more. The islands are separated from the main land by a shallow sound, bay or lagoon. Barrier islands are often found in chains along the coast line and are separated from each other by narrow tidal inlets, such as the Outer Banks of NC.

The formation of barrier islands is complex and not completely understood. The current theory is that barrier islands were formed about 18,000 years ago when the last Ice Age ended. As the glaciers melted and receded, the sea levels began to rise, and flooded areas behind the beach ridges at that time. The rising waters carried sediments from those beach ridges and deposited them along shallow areas just off the new coast lines. Waves and currents continued to bring in sediments that built up, forming the barrier islands. In addition, rivers washed sediments from the mainland that settled behind the islands and helped build them up.

Photo courtesy USGS
Various zones of a typical barrier island

The structure of a typical barrier island consists of the following zones from the ocean side toward the sound:

  • Beach - consists of sand deposited by the actions of waves
  • Dunes - formed from sand carried and deposited by winds. Dunes are stabilized naturally by plants (sea oats, bitter pancum) and artificially by fences. The primary dune faces the ocean and may be followed by secondary and tertiary dunes inland.
  • Barrier flat - (also called backdune, overwash or mud flat) formed by sediments that get pushed through the dune system by storms, such as hurricanes. Grasses grow and stabilize these areas.

Photos courtesy USGS
Storms push sediments through to form the overwash

  • Salt marsh - a low-lying area on the sound-side of a barrier island. Salt marshes are generally divided into high and low marsh areas. High marsh areas get flooded twice each month with the spring tides, while low marsh areas get flooded twice daily with the high tides. Cord grasses stabilize the salt marsh area, which are one of the most ecologically productive areas (amount of vegetation per acre) on Earth.

Barrier islands serve two main functions. First, they protect the coastlines from severe storm damage. Second, they harbor several habitats that are refuges for wildlife. In fact , the salt marsh ecosystems of the islands and the coast help to purify runoffs from mainland streams and rivers. Each of these habitats has distinct animal and plant life, which we will discuss in the next section.

The Shifting Sands
Barrier islands are constantly changing. They are influenced by the following conditions:

  • Waves - deposit and remove sediments from the ocean side of the island
  • Currents - longshore currents that are caused by waves hitting the island at an angle can move the sand from one end of the island to another. For example, the offshore currents along the east coast of the United States tend to remove sand from the northern ends of barrier islands and deposit it at the southern ends.
  • Tides - move sediments into the salt marshes and eventually fill them in. Thus, the sound sides of barrier islands tend to build up as the ocean sides erode.
  • Winds - blow sediments from the beaches to help form dunes and into the marshes, which contributes to their build-up.
  • Sea level changes - rising sea levels tend to push barrier islands toward the mainland
  • Storms - storms have the most dramatic effects on barrier islands by creating overwash areas and eroding beaches as well as other portions of barrier islands.


Photo courtesy USGS
Changes in Louisiana's Isle Dernieres barrier island before (top images) and after (bottom images) Hurricane Andrew in 1992. The arrows indicate identical, corresponding points on the top and bottom images.

The impacts of storms on barrier islands depend upon qualities of the storm (storm surge, waves) and upon the elevation of the barrier island at landfall. To quantify the impact of storm damage, the U.S. Geological Survey (USGS) has devised a "hazard scale" as follows:

  • Impact 1 - Wave erosion is confined to beach area. The eroded sands will be replenished in a few weeks to months and no significant change occurs in the system.
  • Impact 2 - Waves erode the dune and cause the dune to retreat. This is a semi-permanent or permanent change to the system.
  • Impact 3 - Wave action exceeds the dune's elevation, destroys the dune and pushes sediment from the dune landward (approximately 300 yards/100 m), thereby creating overwash. This change in the system pushes the barrier island landward.
  • Impact 4 - The storm surge completely covers the barrier island, destroys the dune system and pushes sediments landward (approximately 0.6 miles/1 km). This is a permanent change to the barrier island or portions of it.


Photo courtesy USGS
The storm impact hazard scale (top left: impact 1, top right: impact 2, bottom-left: impact 3, bottom-right: impact 4)


2. Cape Hatteras 1:250,000 B & W topographic map and Buxton and Cape Hatteras 1:24,000 topographic map

Examine the Raisz map and note the string of offshore islands from the south shore of Long Island to the Mexican border. These barrier islands are famous for their beaches and other types of recreational activities. They are fragile, yet persistent, features of the Atlantic and Gulf coasts. They are particularly dangerous places when hurricanes sweep the coastlines. Find Capt Hatteras, N. C. on the Raisz diagram and the topographic maps.

1. Geomorphic Province:  Coastal Plain

2. a. What is the geomorphic name for Cape Hatteras? (cuspate foreland)

    b. 1. Is Cape Hatter an example of a prograding or retrograding shoreline. (prograding)

        2. Explain your answer to b1. (Cape Hatteras is being extended into the Atlantic Ocean)

    c. What is the geomorphic name for Hatteras Island? (barrier island) The barrier islands off North Carolina's coast are called the Outer Banks.

    d. Note how the 30 and 60 foot bathymetric lines (underwater contours) outline the full dimensions of the islands and cape.

    e. 1. What is the width of the surface expression of Cape Hatteras? (3.5 miles)

        2. What is the width of the surface and sub-surface expression of Cape Hatteras? (15 miles)

    e. 1. Cape Hatteras is being built out into the Atlantic Ocean. Note the shape of the point of the cape on the two topographic maps. The B & W map was made from 1972 aerial photographs and the 1:24,000 map was made from 1946 aerial photographs. What difference in the shape of the cape do you see between the two maps? (Very smooth symmetrical point on the 1:24,000 map and a projection to the south on the 1:250,000 topographic map. )

    2. What would the symmetrical shape in 1946 suggest about the balance between currents moving from the north and from the south along the shoreline? (That the current movements would have been balanced and thereby produced the symmetrical point.)

    3. What does the extended point on the 1:250,000 map suggest in terms of a balance between currents that move from the north and the south along this shoreline? (There does not seem to be a balance between the currents from the north and the south and the current from the north appears to be stronger than the current from the south between 1946 and 1972 because the extension of the point in a southerly direction is prevailing over currents that would push the point eastward.

3. a. What is an average width of the surface expression of Hatteras Island? (about 1 mile to 1.5)

    b. What is an average width for the surface and sub-surface expression of Hatteras Island? (4-6 miles)

    b. If you drove Route 12 along Hatteras Island how close would you be to sea level most of the time? (Within 10 ft.)

4. Assume you were at Cape Hatteras and had a medical emergency, called 911 and EMT's left from Norfolk to come to your aid. About how far would they have to travel to come to your assistance? (About 75 miles)

5. Why would the National Park Service personnel call for an evacuation of the barrier islands in the event of a hurricane? (The storm surge can easily overtop the barrier islands and remake the landscape. Some before and after pictures of the same area after a severe hurricane have barely recognizable points in common.)

6. Kitty Hawk is just to the north of your B & W map. It was isolated in 1900, but has become a famous tourist area with many structures close to the water and in harms way when severe storms move along the North Carolina shoreline.

Once a remote area, Kitty Hawk has grown into a summer resort area and provides some of the best beach recreation on the North Carolina Coast.

When Orville Wright stepped ashore in Kitty Hawk Village in the fall of 1900, he probably already knew that he and his brother were destined to make history as discoverers of flight. After all, they had chosen this remote fishing village on the Outer Banks partly for privacy from prying eyes. Three years later, they would indeed break the bonds of earth for the first time in their heavier than air flying machine.

From that moment forward, Kitty Hawk would forever be associated with the Wright Brothers as the birthplace of aviation -although the actual flight took place four miles south from the base of Kill Devil Hill. Today, the once-tiny sea  side village is one of the largest townships on the Outer Banks. On the oceanside, thousands of rental homes, restaurants and shops are part of the development that has characterized the northern Outer Banks from Nags Head to Corolla.

Read the following about Cape Canaveral.


Plate C-14


Plate C-14


Cape Canaveral is the southernmost of the cuspate forelands on the U.S. Atlantic coast barrier system. It is the site of Cape Kennedy Air Force Station and NASA's Kennedy Space Center (KSC). The cuspate foreland has officially reverted to its traditional name after being called Cape Kennedy for a few years in the 1960s. Numerous rocket launch pads are visible in the false-color Landsat scene as uniformly spaced light patches along the shoreline of the Cape. Views of the coast up and down from the Cape appear in Figure C-14.1 and Figure C-14.2. More details in and around KSC are visible in the Landsat RBV image reproduced in Figure C-14.3.

Cape Canaveral is approximately the southern limit of quartz- rich detrital sand transported southward from rivers that drain the coastal plain, the piedmont, and the Appalachian Mountains of the southeastern states. Most of the detrital sediment of Cape Canaveral is mixed with and bound together by weakly cemented biogenic limestone. Masses of broken mollusk shells cement easily by ground water to become coquina, a shelly conglomerate that may be strong enough to be used as a building material or to protect fossil beach ridges from later erosion. The weakly cemented mixture of detrital quartz and biogenic limestone is so resistant to erosion that several generations of the ancient beach ridges that predate Cape Canaveral can be easily traced in the view.

The oldest fossil shoreline is a series of detrital sand ridges that trend slightly east of south through western Orlando and Haines City. Rising 50 to 60 m above present sea level, these ridges are deeply weathered and leached of any former carbonate material. They may be as old as Pliocene or Late Miocene age (perhaps 3 to 5 Ma) (MacNeil, 1950). The sandy cover of central Florida frequently collapses into karst sinkholes in the underlying Ocala limestone, with disastrous results (Plate KL-4). The maze of lakes in the central part of the image are karst sinkholes, by the generally high rainfall of the region and the low relief that inhibits ground-water movement.

A second series of fossil barrier ridges can be traced between Orlando and the St. Johns River. These have most recently been referred to as the Effingham Sequence, named for Effingham County in Georgia (Winkler and Howard, 1977). They are generally below 30 m altitude and have been correlated with the Wicomico and Waccamaw formations of Georgia and South Carolina. They are estimated to be of Early Pleistocene age, between 1.0 and 1.7 Ma old. The Effingham beach ridges are distinctive in that they show a series of cuspate forelands of dimension similar to Merritt Island and Cape Canaveral.

Between the St. Johns River and Indian River, and including Merritt Island, is the next younger series of ancient beach ridges. These ridges, named the Chatham Sequence by Winkler and Howard (1977), show a well-developed cuspate foreland in Merritt Island, now truncated by Cape Canaveral except where the modern barrier is deflected seaward by the resistant cemented coquina beach ridges at False Cape. A few radiometric dates on poorly preserved mollusk shells suggest that this sequence, now less than 10 m above sea level, is about 100 000 years old. It was probably built during the last interglacial interval when sea level was a few meters above the present level (Osmond et al., 1970). Although the older higher beach ridges inland require a slight amount of tectonic uplift over the past few million years, the Chatham Sequence could have been built during a higher sea level, rather than having been uplifted in the last 100 000 years. These are probably of the same ages as the ridges that control the Sea Islands of Georgia and South Carolina, and are buried under the modern barriers of Cape Hatteras.

Thus, as noted in Plate C-13, the modern barriers on the southeastern U.S. coast are only the latest of a long series of such forms that were built in the Tertiary Period as the coastal plain gradually accumulated sediment and prograded seaward. But during the Pleistocene Epoch, the repeated rise and fall of sea level through a range of 100 m in harmony with each ice age has complicated the longer term progradation. Each ice age exposed most of the shelf, and rivers extended their lower valleys nearly out to the shelf margin (Field and Duane, 1974). As sea level rose, the shoreline again migrated landward. Especially in the last 5000 to 6000 years, the most recent rise of sea level has driven older barrier systems landward across the shelf or overtopped them to form newer barriers near the transgressing shoreline. In many regions, the youngest Holocene barriers have been stabilized by older eroded barrier segments. Like the cuspate forelands of Cape Hatteras and the Sea Isles, the modern Cape Canaveral foreland has probably accreted and migrated southward in the last few thousand years, although massive construction at the Kennedy Space Center has now destroyed many of the prehistoric beach ridges on the Cape. Landsat 1045-15275, September 9, 1972.

3. Cape Canaveral 1:250,000 topographic map.

1. Geomorphic Province: (Coastal Plain)

2. a. What is the geomorphic term for Merritt Island and Cape Canaveral. (Cuspate foreland)

    b. Note how the 30 foot bathymetric line outlines the underwater portion of the features.

    c. Which of the features is the older? (Merritt Island)

    d. What map evidence did you use to answer 2b? (The barrier island to the north of Cape Canaveral is built across the seaward projection of Merritt Island.)

    e. The shoreline currents along the east coast of Florida predominantly move sand from north to south. How does the surface, and underwater, shape of Cape Canaveral demonstrate that the predominant direction of the shoreline current is from north to south? (The underwater extension projects prominently to the southeast which indicates a stronger current from the north than from the south.)

3. a. What two government facilities are located on Cape Canaveral? (Cape Kennedy Air Force Station and NASA's Kennedy Space Center.)

    b. Note the approximately 20 sites, the small circles, from which rockets can be launched. This site was chosen from which to launch rockets because it is on the east coast and the most southerly site that is suitable. A southerly location requires less engine power than a more northerly location because the coriolis effect diminishes to zero at the Equator. The easterly location also allows the lift off to take advantage of a "sling-shot" effect because the earth is rotating from west to east at approximately 915 miles per hour at this latitude.

    c. The historic name for the cuspate foreland is Cape Canaveral. During the 1960's, in an emotional outpouring after President Kennedy's assassination, the cape was called Cape Kennedy, but there was objection to renaming the cape and the Board of Geographic Names ruled that the physical feature on which the air force and NASA facilities were built should keep the original name. At this point the U. S Air Force Station and the NASA facility were given their current names in honor of President John F. Kennedy because it was under his administration that the decision was made to place a man on the moon. The Kennedy Space Center is the facility from which all the Mercury Apollo, and shuttle missions have been launched. It is also the primary landing site for the shuttle missions, but if weather does not permit landing in Florida a back-up site is used in California at Edward's Air Force Base. When the shuttles land in California they are piggy-backed back to Florida atop a specially fitted Boeing 747.

    d. Note the Intracoastal Waterway that runs from north to south inland from the barrier islands, Merritt Island, and Cape Canaveral. This waterway (ditch) was dug during World War II to allow ships and barges to travel safely along the Gulf and Atlantic coasts without being attacked by German submarines. The intracoastal is used today by pleasure craft and barge traffic.

Read the following article on Point Reyes, CA

The Make-up of Point Reyes

by Jeff Scattini


Thirty five miles north of San Francisco is a very large rock known as Point Reyes. Like most Bay Area residents, Point Reyes is not a native: it settled in this area more than 330,000 years ago. Walking along the coastline of this transplanted shore, you notice things; a high ridge of hills, red, sandy rocks, and a series of steps cut into the landscape, as if a giant had wanted to make

an easier path to the top of the ridge. Walking farther, you notice that a hole has been dug in one of these steps. You climb up about 50 feet to the first of these odd flat planes. Stepping closer and peering into the hole, you see what you had expected—dirt—but also two things you hadn’t expected at all: old beach sand and a geologist.



The sand is dry and brittle and has been in that hole for the past 80,000 years. The

geologist has been in the hole since seven o’clock that morning. Her name is Karen

Grove, Ph.D., and she is a professor at San Francisco State University. You help her out of the hole, and, as she brushes the sand of the ages from her clothes into a carefully labeled specimen jar, she begins to explain. Grove first noticed the peculiarities of the

Point Reyes coastline during a 1993 sediment survey of Point Reyes, looking for evidence of seismic activity over the past 100,000 years. She was struck by the terraces on the flank of the peninsula. Marine terraces are formed when the ocean cuts away at the land, explains Grove. Slowly, over thousands of years, the ocean forms a flat plane in the landscape. This flat plane is the beachfront where, today, people come and relax and play. Then, perhaps every thousand years or so, an earthquake lifts the land up above sea level. As this happens, the sea level recedes. When the sea level rises again, it starts to cut into the land again. Since the previous ground level is now above sea level, the ocean must start fresh. Once again, over thousands of years, the ocean creates a flat plane in the landscape. Again, an earthquake raises the land above the ocean’s reach, and then the ocean, again, must begin leveling the beach. This continual leveling and raising of the beachfront creates the terraces that form the flank of Point Reyes. How did Grove figure out the age of the coastline? The sediment of the coastline is not like trees where the rings of the trunk will tell how long they’ve been around. Normally, when geologists want to know the age of a coastline, they try to find seashells that have been thrown up by prehistoric oceans. Scientists can carbon-date the shells, a process in which they count carbon atoms and see how many have decayed. (The more atoms that have decayed, the older the artifact is.) Grove never found any seashells. Instead, she chose another way of dating the Point Reyes coastline, called luminescence dating. Luminescence dating, or glow studies, relies on the fact that certain crystals trap the natural radiation of the earth, explains Grove. This radiation is released when the crystals are heated or exposed to sunlight. When these crystals are hidden away from the light, say, buried beneath the topsoil of Point Reyes, the crystals start trapping the natural area radiation. The radiation will build up in the crystal until it is either exposed to sunlight or heated to over 500 degrees Celsius. When scientists take a sample of these crystals and expose it to specific lights and temperatures, the sample will luminesce, or glow, and the amount of light and radiation escaping will tell them how long the crystals have been hidden from the sunlight. Grove and her team must take care when gathering these samples. Any exposure to light or extreme heat will ruin the samples, so Grove uses thick PVC pipe and an impressive amount of duct tape to secure them during transport. To get the samples from the terrace, she crawls under a large black cloth, hammers a PVC pipe into the cliff face, and then, in the pitch black, wraps them in black plastic and duct tape. With her  prehistoric beach terraces blowing out their ancient birthday candles, Grove must then determine how much uplift has occurred to each terrace. There is nothing better than a Global Positioning System (GPS), which uses satellites to determine the precise longitude, latitude, and elevation of a millennium-old beach terrace. Using a GPS,

Grove and her team took over 100 elevation Diagram of marine terraces, which have two components–a platform carved by waves in the surf zone, and sediments that accumulate on top of the platform. Along an uplifting coastline, the platform and sediments get moved vertically upward from the surf zone, so that new platforms are created at lower elevations. The uplift rate of the coastline can be calculated by measuring the elevation of the uplifted platform and dividing by the age when the platform was created. All diagrams courtesy of Dr. Grove Karen Grove, Professor Department of Geosciences

points at three different locations on the most recent terrace. Over time, they emerged with a set of data that detailed the amount of uplift each site on the terrace had experienced in the last 80,000 years. Grove discovered that different areas of Point Reyes are rising at different rates. The three sites, Wittenburg, Glen, and Bolinas, had elevations of 10.2 meters, 28.9 meters, and 84.5 meters above sea level. Grove’s calculations show the three different sites uplifting at 0.2 millimeters, 0.4 millimeters, and 1.1 millimeters per year, respectively. Grove found that uplift has been most responsible for the unique triangle shape of Point Reyes. “Point Reyes is like a cupped hand,” Grove explains, holding her own hand out for demonstration. “As uplift occurs, the two ridges get taller and the valley forms.” By measuring the height of the different terraces, Grove can estimate the amount of uplift that has occurred to give Point Reyes its distinctive

shape. Once she knows the amount of uplift in a given time frame, she can estimate the

amount of seismic activity that the area has had in the past 80,000 years. Listening to this animated woman describe the seismic antics of the landscape, you look out over Point Reyes with new eyes. You envision Point Reyes sliding farther up the coast and becoming Canadian. You ask about the San Andreas Fault, which could cause the earthquakes that make this type of shift. Grove acknowledges the possibility of earthquakes from the fault, which she says is “a major player,” but she is more interested in other fault-lines. Other fault-lines? There are smaller faults that allow vertical motion in the Point Reyes region and are responsible for its topography. These smaller faults are considered part of the San Andreas Fault System. The smaller faults’ significance is poorly understood, and little is known about how they interact with the overall system. By studying how these fault-lines helped shaped Point Reyes, Grove hopes to investigate faults that have similar characteristics and see how they interact with the major San Andreas Fault. Point Reyes is like a cupped hand. As uplift occurs, the two ridges get taller and the valley forms.” Along with furthering recognition of hazardous fault-lines, Grove’s research will educate people about how the Bay Area landscape has formed. She would like to install three-dimensional animated topographical maps in the Point Reyes ranger station so that every visitor can easily see how the Point Reyes

landscape has evolved. She pats the rocks around her, imagining that wealth of information displayed for the public. As the sun dips lower on the horizon, Grove says goodbye and drops down into her hole to take the last samples of the day. You walk along the coastline and begin noticing the tall ridge, the sandy red rocks, and the surrounding ocean in a whole new light. Placing your hand on the bare earth, you can almost feel the intricate interplay of the shifting fault-lines, their resulting earthquakes,

and the rising sea levels, which together have cut into and uplift the landscape, creating terraces, and over thousands of years, formed this remarkable bit of rock. 1 Above: Marine terraces are used to estimate the rate of vertical uplift of the Point Reyes Peninsula and the timing of its emergence from the sea (ka= thousand years ago). About 330,000 years ago, the Point Reyes Peninsula consisted only of a single small ridge west of the San Andreas Fault. Since then it has been uplifted by faults to become a larger area above water. The white area between the peninsula (shown in darker gray) and

the Marin County mainland (shown in gray) is the valley created by the San Andreas Fault. Schematic diagram of the paleogeography of the San Andreas Fault valley south of Tomales Bay. gr=Mesozoic granodiorite, Qoc=Pleistocene Olema Creek Formation.


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4. Point Reyes, CA Topographic Map

1. Geomorphic Province: (Pacific Border Province)

2. a. What kind of tectonic activity is present in this area? (Faulting)

    b. Because of the tectonic activity this coastline is very different from the East Coast and Gulf Coast. Which specific tectonic feature runs diagonally from NW to SE? (San Andreas Fault)

    c. On the east coast maps you saw more evidence of shoreline deposition than erosion. At Point Reyes there is clear evidence of shoreline erosion. Point Reyes is an example of a retrograding shoreline. List two topographic features that indicate erosional, or retrograding activities. (Chimney Rock, and other similar features, and the steep south facing cliff.)

    d. Go to http://stuff.mit.edu/people/dankan/ images/Point%20Reyes/images/ and view images of Point Reyes. The lighthouse image is the Coast Guard Reservation at the southwestern tip of Point Reyes. The rocky cliffs are along the southern edge and the other shoreline scenes are most likely along the western shoreline.



3. Drakes Estero, Point Reyes National Seashore, California


Tidal channels and mudflats exposed at low tide in the upper reaches of Drakes Estero, a drowned river valley. During the Pleistocene glacial epochs, worldwide sea levels were lowered as much as 425 feet. Water was removed from the oceans to form vast continental glaciers. During periods of lowered sea level, valleys were eroded and deepened in shallow offshore and coastal regions. As the glaciers melted and sea level rose again, the deeper valleys were flooded. A drowned river valley is an estuary - a coastal water body that is open to the ocean and is diluted by fresh water from the land.

    a. What drainage pattern does Drakes Estero portray? (Dendritic)


    b. How was Drakes Estero formed? (See text above.)


    c. What does Limantour Spit suggest about the prevailing shoreline current in Drakes Bay? (The spit is being extended westward which indicates a current moving northwestward and then westward.)


    d. Note how the spit curves toward Drakes Estero at its western end. What might this suggest about the strength of the incoming tide vis-à-vis the strength of the outgoing tide?

(The incoming tide is probably stronger than the outgoing tide as indicated by the northward bend of Limantour Spit. The curvature at the north end of Drakes Bay would favor a high tide as the water is being forced into a narrower area.)


4. See the diagram of marine terraces. This diagram would represent a view from the Pacific Ocean inland. The modern beach, wave-cut platform, and sea cliffs would be directly on the ocean and the terrace surface, beach deposits and old platform and paleo-sea cliffs represent topographic features that were at sea level in the past but have been uplifted and now stand well above sea level. One of the best areas to see these features is on Tomales Point where the old beach deposits and old platform are outlined by the 400 foot contour line.















5. The beaches at Point Reyes are long and narrow and the sand dunes along the Pacific Ocean add greatly to the beauty of this National Lakeshore.


Point Reyes National Seashore contains unique elements of biological and historical interest in a spectacularly scenic panorama of thunderous ocean breakers, open grasslands, bushy hillsides and forested ridges. Native land mammals number about 37 species and marine mammals augment this total by another dozen species. The biological diversity stems from a favorable location in the middle of California and the natural occurrence of many distinct habitats. Nearly 20% of the State's flowering plant species are represented on the peninsula and over 45% of the bird species in North America have been sighted. The Point Reyes National Seashore was established by President John F. Kennedy on September 13, 1962.

5. Sagatuck, MI Topographic Map


1. a. What structure has been built at the mouth of the Kalamazoo River? (jetty)


    b. What two purposes does it serve? (stabilize the mouth of the Kalamazoo River and speed up the movement of water through the jetty to help keep the channel bottom scoured and thereby reduce the amount of dredging)


    c. 1. Do the sand deposits on either side of the structure indicate a prevailing current along this section of the shoreline? (no)


        2. Justify your answer. (the deposits on either side of the jetty are balanced which indicates a wind from a northerly component, mostly northwest, being balanced with a wind with a southerly component, mostly southwest.)


2. a. Note the little community of Oxbow in Sec. 4, T3N, R16W. How do you think it got it's name? (old oxbow of the Kalamazoo River)


    b. Draw an estimation of how the Kalamazoo River might have entered Lake Michigan at some time in the past. How does the Old Sagatuck Light House fit into the picture?








3. a. How can you account for Kalamazoo Lake and the wetland area, and sinuate course of the Kalamazoo River in Sec. 13, 14, & 15, T3N, R16W? (The Kalamazoo River does not have an easy time getting through the coastal dunes. The depositional action of the waves could be strong enough at times to dam the river if the jetty system were not in place. The damming action at the mouth of the stream causes the water to back up and make Kalamazoo Lake and the wetland in the lower valley of the Kalamazoo River.)


    b. Which seems to have dominated in this area, the force of running water or the force of the waves and wind building the beach and dunes? (the waves and wind)


    c. Explain your answer. (The dunes are quite large here which indicated a good supply of sand that is brought in by the waves and built into dunes by the wind. The fact that the Old Saugatuck Lighthouse is not at the mouth of the stream indicates that the mouth of the stream must have been here at some time in the past. If the jetty system were removed the mouth of the stream would likely change from time to time with the coming and going of major storms, which most often occur in November.)


6. Frankfort, MI Topographic Map


1. a. What was built at the mouth of Betsie Lake? (jetty)


    b. Note the contrast between the two sides of the structure on this map as compared with the balance on either side of the structure at Saugatuck. This map shows prograding on the northern side and retrograding on the south side. What does this suggest with respect to the direction of the prevailing winds and shoreline current in this area? (The prograding on the northern side and retrograding on the south side indicate a stronger current from north to south than from south to north.)


    c. 1. What was built into Lake Michigan at a later date to offset the damage done by the earlier structure? ( a breakwater)


        2. Does it appear to have solved the problem retrogrdation? (yes) What is the basis for your answer? (The shoreline is quite balanced on either side of the breakwater.)


2. Note the large concentration of railroad tracks at Elberta. This was one of the west Michigan places where you could take a ferry from Michigan to Wisconsin. The ferry's were built to haul railroad card and only switched to automobiles as the railroad business faded. The large ferries justified building the breakwater as they need quiet water to safely navigate the narrow entrance into Betsie Lake. The ferry service from Elberta is now a memory and the vast majority of traffic on Betsy Lake is now pleasure craft. You can still ride a rail ferry from Ludington, MI. to Manitowoc, WI., but its days of carrying rail road cars is long gone. You can also take a high speed ferry from Muskegon to Milwaukee.


3. a. What is the elevation difference between Crystal Lake and Lake Michigan? (183 meters-Crystal Lake, 177 meters for Lake Michigan)(600.42 ft. for Crystal and 580.74 for Lake Michigan)


    b. Crystal Lake covers nearly 10,000 acres. An acre of water is 43,560 square feet. Suppose you wanted to drain Crystal Lake to the level of Lake Michigan. How many cubic feet of water would you have to remove from Crystal Lake? ( 43,560 X 10,000 X = 435,560,000 cubic feet of water X 20=871,120,000 cubic feet of water)


    c. What would happen if you tried to empty this much water through a narrow channel into Lake Michigan? (you would have a major flood on your hands)


d. This is exactly what happened during the lumbering era. A saw mill was located near the eastern end of Crystal Lake. The cut lumber was hauled by horse drawn wagon to the Lake Michigan shoreline where it was then loaded onto a lake steamer. The owner of the sawmill thought it would be a good idea to have the steamers come to him rather than him hauling the wood to Lake Michigan. He hired a steam dredge to begin cutting a ditch from Lake Michigan to Crystal Lake. As the ditch neared Crystal Lake the water let loose and went rushing into Lake Michigan. The dredge operator fortunately escaped with his life, but the current was so strong that boats on the lake ran to the Wisconsin shoreline to avoid being swept where they did not want to go. The disaster is memorialized with the historical marker in Beulah (Fig. 1). The place where the water rushed through is in the southeastern part of the map where you see Crystal Lake Outlet. The level of the lake is now maintained by a concrete dam Sec. 20, T26N, R15W. A photograph of the dam is shown in Fig. 2.


Fig. 1. At the public beach park in downtown Beulah.


The Dam where Crystal Lake "ran out" in the tragedy of Crystal Lake, 1873.

4. a. Examine Platte River Point in the northeast portion of the map. What direction of shoreline current is indicated by the point? (west to east)

    b. Which seems to have the most energy at this point, the waves of Lake Michigan or the waters of the Platte River? (the waver of Lake Michigan)

    c. Explain your answer. (The Platte River is a short river with a low gradient. It has almost no down cutting power and follows a wandering path to Lake Michigan. The waves can "push" the mouth of the river from side to side as the storms come and go. As this area is in the Sleeping Bear Dunes National Lakeshore the river and shoreline are left to the forces of nature. On any given day you might find the river in this position or you might find it entering Lake Michigan by flowing westward.

    d. This map was made in 1983. If you visited the area today you might find the Platte River Point as you see it on the map, but do not be surprised if it is different because the point is a small and fragile feature that is moved by the waves as they come from different directions as the winds shift.

7. Michigan City West, IN Topographic Map and B & W copy of lakefront.


1. What has been installed at the mouth of Trail Creek? (jetty)


2. a. What is the structure called that is offshore with lights at both ends? (breakwater)


    b. What does it break? (the energy of the waves approaching the entrance to Trail Creek and the marina)


3. a. Note the offset of the shoreline on either side of Trail Creek. What does this suggest about the direction of the prevailing longshore current in this area? (the prograding condition on the east side indicates a current from east to west)


    b. The prograding condition to the east has built a wide smooth beach for the people to enjoy and protect the beach houses shown close to the shoreline near the eastern edge of the map.


    c. The retrograding condition on the west side of Trail Creek has been due to shoreline erosion as the current moved westward after dumping its load of sand on the east side of Trail Creek. The power plant has protected its site with a steel wall on the lake side, but to the west at the end of the steel wall the erosion continues. Note the recession beyond the steel wall in Sec. 30. T38N, R4W.


    d. Note Lake Front Drive near the western edge of the map. Follow it eastward to where it ends in Sec. 35, T38N, R5W. This road used to continue to Michigan City. Note the absence of beach front houses eastward from where the road ends. The road, and houses on both sides of the road were taken out by a series of storms that generated waves as high as 14 feet. The area became incorporated into the Indiana Dunes National Lakeshore and large rocks were hauled in to stabilize the base of the dunes as the beach had been completely washed away and the waves were destabilizing the dunes, which are the center piece of the lakeshore.


4. a. Measure the amount of offset from the Yacht Basin to the position of the shoreline west of the steel wall in Sec. 30, T38N, R4W. How many feet of shoreline change has resulted from prograding conditions east of the Yacht Basin and retrograding conditions west of the steel wall? (3,500 feet which is about .65 mile)


    b. This is the most extreme situation that I know of on Lake Michigan which shows the negative consequences of shoreline "protective" devices, which map protect one area, but cause a negative impact downwind from the protected spot.