By Nelson Rangel-Buitrago, Grupo de Geología, Geofísica y Procesos Marino-Costeros, Universidad del Atlántico Barranquilla, Atlántico, Colombia and William J. Neal, Department of Geology Grand Valley State University Allendale, Michigan.

Colombia’s Caribbean coast has a rich geological, biological and cultural diversity that is reflected in the complex coastal zone extending from the border of Panama to that of Venezuela. One of the most spectacular regions in both this diversity and scenery is the Tayrona National Natural Park (TNNP), a coastal reach of the Sierra Nevada de Santa Marta, the highest coastal mountain range in the world, with peaks topping out at 5,700m (18,700 ft). This mountain complex stands separate from the related Andes, and forms the seashore along its northern border. The rugged, remote area was a barrier to settlement, and has remained a natural Eden in terms of ecozones and the rich diversity of its flora and fauna. Fortunately, the Colombian government recognized that the 20th century’s rapid increase in expanding settlements and urbanization were threatening the country’s natural areas, and established a system that now comprises 59 National Natural Parks, protecting 126.023 km2 equivalent to 11% of the country’s total surface area. Tayrona National Park is perhaps the most famous of these parks, and is the gem of the Caribbean coast in terms of its scenery and diversity of both terrigenous and marine life. Created in 1964, TNNP stretches along the coast from the western Bahía de Taganga near Santa Marta city to the mouth of the Río Piedras, 35 km to the east, and covers some 120 km2 of land and 30 km2 of the sea (Figure1).

TNNP is the northwest coast of the Sierra Nevada de Santa Marta, and the area of the park corresponds to a complex geologic zone underlain by Cretaceous metamorphic rocks and Tertiary igneous intrusives. Valleys formed from streams eroding weaker rocks, or by erosion along faults, and were flooded to produce the long embayments and coves, particularly in the western part of the park, between the resistant headlands. These ridges terminate at the coast, often in seacliffs 100 to 150 m (330 to 490 ft) high (e.g. Arrrecifes, Cañaveral, Chengue, Gayraca, Cinto, Neguanje, Concha, Guachaquita). These rocky coasts have a variety of other erosional features such as sea stacks, scarps, shore-platforms and large granite boulders strewn along the shore (Figure 2).

“The wide variety Fauna in the two ecosystems, from mountains into the sea, includes fascinating wildlife such as the black howler and titi monkeys, red woodpeckers, iguanas, jaguars…”
— N. Rangel-Buitrago & W. J. Neal

The combination of geology and the varied climatic zones due to the ranges of coastal orientations, topographic elevations, and rainfall (0 to 975 mm/yr (38 inches), creates the scenery, and varied ecozones. The extreme western part of the park is arid, with light-brown hills and xerophytic plant species such as cacti. The central and eastern parts of the park are wetter and more verdant, widely covered by rainforest. May, June, and September to November are the wettest periods. The Flora is characterized by this environmental influence of rainfall depending on the sector, from tropical dry forest to rain forest and mangroves.

The wide variety Fauna in the two ecosystems, from mountains into the sea, includes fascinating wildlife such as the black howler and titi monkeys, red woodpeckers, iguanas, jaguars (which are rarely seen as they hunt at night), a variety of lizards, tropical marine life including reefs, and more than 400 species of birds, such as eagles, condors and the odd pet parrots kept at the restaurant at Arrecifes. Below the clear waters is an array of marine life, popular with snorkelers. All of these features provide an ideal place to commune with Nature, and activities include beach combing, snorkeling, boating, fishing, and diving. Hiking trails provide access for birding, exploring nature, and visiting archeological ruins of an ancient city of the Tayrona people. This palate of beauty, both landward and seaward of the shore, makes the Tayrona beaches an experience unique (Figure 3).

And the more than 20 beaches are the park’s biggest attraction, linking the stunning scenery of mountains, clear blue to azure water conditions, white to golden sands (derived mainly from weathered granite cliffs), creek mouths, and back-beach vegetation (Figure 3). The beaches range from linear, to large pocket beaches at the ends of the longer bays and smaller pocket beaches in coves (Figure 4).

Western Beaches

The great elongate bahias (bays) characterize the western shore of the park (Figure 4). Typically large pocket beaches have formed on the most inner-shores of these bays, but smaller coves on their margins sometimes have pocket beaches. Access is by car from the city of Santa Marta and by boat from Taganga.

Playa Concha, a long pocket beach, is the most popular western beach because there is easy access and facilities (Balneario de Villa Concha). The area is popular for swimming and boating (Figure 5).

Bahia Chengue has a couple of smaller pocket beaches. Its only entry point is by using maritime transportation, but the access to this beach is prohibited because it is the biggest Coral Reef reserve in Tayrona park.

Bahia Gairaca also has two pocket beaches, Playa Hermosa and la Playa del Amor (Figure 6).

Bahia Neguanje looks like a double-wide embayment compared to adjacent Bays, and has three well-developed pocket beaches. Seven Waves Bay owes its name to the strong waves and rip currents there that severely limit maritime activities (Figure 7). In addition, on its eastern flank are Playa Cristal and Playa del Muerto, small white pocket beaches fronted by clear water of blue and green hues, and popular with snorkelers and boaters.

Playa Cinto is the pocket beach at the terminus of the last long embayment to the east. The blue water contrasts with the dark creek, and the area is a good example of the dry-climate vegetation (Figure 8). Cinto and Neguanje are distant by road access. A few additional pocket beaches are located farther east, but lack of access deters beach users.

Eastern Beaches

Road access to the park is limited, and the main eastern entrance provides parking, and then access to the beaches and associated campgrounds is by foot or horseback. Several linear beaches, often with associated creek mouths, occur in this area including Playa Tayrona and the following:

Playa Castilletes, located nearer to the east entrance road, is usually used as a small camping area, convenient to Playa Canaveral.

Cabo San Juan de Guia is a tombolo and the most famous beach of the park; here many visitors spend most of the time because of the scenery and an ideal swimming beach (Figure 9). The beach is on the west side of the cape, as well as a couple of small half-moon coves with pocket beaches.

Playa La Piscina, a small beach located between Arrecifes and Cabo San Juan, is a busy and popular beach because the calm water conditions favor safe swimming (Figure 10). Also, the location is convenient to most all of the eastern park’s campsites.

Arrecifes beach is one of longest stretches of beach in the eastern part of the park (Figure 11), and one of the most popular. Great rounded granite boulders add to the scenic beauty (Figure 12), and during the rainy season there is a freshwater lagoon behind the beach, where alligators can occasionally be glimpsed.

“The more than 20 beaches are the park’s biggest attraction, they range from linear, to large pocket beaches at the ends of the longer bays and smaller pocket beaches in coves…”
— N. Rangel-Buitrago & W. J. Neal

Playa Cañaveral is another beach offering accommodations, but generally has fewer visitors than most of the other beaches in the park. This long beach is much narrower than other beaches in the area, but is a tranquil setting with palm trees, a thin strip of white sand and the turquoise ocean. Here beachcombers will find patches of dark heavy-mineral sands and interesting wrack lines (Figure 13).

Safety

As with all beaches, approach with caution. Take into account the possibility of rip currents (Figure 14). Some of the Tayrona beaches are not suitable for swimming, though you can take a dip and snorkel (with great care) at selected sites. Refer to the Park rules and warnings before your visit (Tayrona National Natural Park web site).

Tourism: what are the limits?

Due to better security conditions, recent peace agreements, and global promotion via the internet, Tayrona Park has become a popular destination for both national and international tourists. Although the inland area of the park has much to offer, the beaches, with Eden as a backdrop, are the areas where visitors congregate. At present, tourism represents one of the most important economic activities, and development capacity appears to be almost limitless. But is it? Park tourism increased from 228,941 visitors in 2009 to 391,442 in 2016, and growth is expected to continue at this pace (Rangel et al., 2013). Such increases in tourism numbers will become unsustainable in the immediate coming years if left unregulated. Uncontrolled tourism into the surrounding areas also will intrude upon both the biota as well as the daily lives of indigenous inhabitants. Already the large numbers of visitors during the high season detract from the world-class charms of the park (Figure 15).

The park attempts to manage human impacts by limiting vehicle access, but heavy use by boaters can offset this in terms of noise, congestion, pollution, and the conflicting use of boats vs. swimmers (Figure 16). Park rules also are aimed at controlling pollution and congestion (e.g., restricting entry of plastic bags, pets, alcoholic beverages, surf boards; requesting visitors to take their garbage and refuse with them when they leave the park), but the numbers of people in camp grounds for example create septic wastes that find their way into surface runoff, groundwater, and into the beach.

Flotsam as seen in wrack lines and in along-shore current deposits show both natural materials, typically brought down by rivers and creeks (e.g., logs, tree limbs, vegetation) as well as waste generated by beach users, boaters, and hikers (Williams et al., 2016). At Seven Waves Bay one can usually find a beach cover of 1000s of items of general litter (Figure 17). This beach is a sink for plastic bottles, shoes, food packaging, ropes, tires, plates, and other plastic and polystyrene materials. In such a case, the adverse effects produced by the litter overcome the aesthetics of the coastal scenery. Stronger actions are necessary to upgrade scenic beach quality (Williams et al., 2016).

In 2015 and again in 2017 the park was closed for short periods to all except for indigenous groups who live within the park area “for ecological, environmental and spiritual healing” (Colombia Travel Blog, 2017), and the suggestion is made that the Park Management should set a cap on the number of visitors within the park at any given time. The “healing” time is also important to the hundreds of species that call the park home, including at least 56 endangered species. A cap on numbers of visitors may sound draconian, but the park’s mission is to protect the natural ecosystems, rather than becoming just another amusement center.

At the same time, natural forces are still at work. Waves, storms, and the sea-level rise continue to erode much of the park’s shoreline, causing shoreline retreat, potential beach narrowing, and flooding (Rangel et al., 2015). The rates of these processes are highly variable, depending on rock types, their degree of fracturing and faulting, and the orientation of the respective shores relative to tectonic features such as faults. What will park management’s response be when one of the main beaches narrows, a campground floods, or a road is threatened by erosion. Hopefully, it will be to let Nature take its course, and for this Natural Park to remain Natural.

References:

• Colombia Travel Blog, January 2, 2017, Tayrona National Park to close for a month.
• Tayrona National Natural Park web site
• Rangel-Buitrago, N., Anfuso, G., Correa, I., Ergin, A., Williams, A.T., 2013. Assessing and managing scenery of the Caribbean Coast of Colombia. Tour. Manage. 35, 41-58.
• Rangel-Buitrago, N., Anfuso, G., Williams, A.T. 2015. Coastal erosion along the Caribbean coast of Colombia: magnitudes, causes and management. Ocean Coast. Manage. 114, 129-144.
• Williams, A.T., Rangel-Buitrago, N., Anfuso, G., Cervantes, O., Botero, C., 2016a. Litter impacts on scenery and tourism on the Colombian north Caribbean coast. Tourism Manage. 55, 209-224.

By Orrin H. Pilkey, James B. Duke Professor Emeritus of Geology, Nicholas School of the Environment, Duke University, Durham, NC, and J. Andrew G. Cooper, Professor of Coastal Studies, School of Environmental Sciences, University of Ulster, Coleraine, Northern Ireland.

All over the world there are beaches lined with condos, hotels, restaurants and the like, in high-rise buildings (i.e., skyscrapers). Such beaches are generally the nation’s premier tourist areas, important to the local people and the local economy and prime spots for national and international vacationers. The powers that be in most of these places continue high-rise construction and seem oblivious of the sea level rise. They do not recognize that a few decades down the road the recreational beach, the raison d’être for the community’s existence, is forever doomed. We discuss this coming calamity in our book The Last Beach.

Famously, the mayor of Miami Beach, Florida, is one local politician who sees the sea level rise as a threat to the future well-being of his community. He has stated that they are seeking high-end (luxurious) developments to provide an ample tax base for responding to the sea level rise in the future. The nature of the response is unclear at this time although there is talk of raising some of the high-rise buildings to allow storm surge waves to pass under them.

The global problem with high-rise-lined beaches is their inflexibility. Realistically the buildings can’t be moved back. It is far too costly to raise or move hundreds of very large buildings to higher ground. Often, there is no place where buildings can be moved back to safety.

“The global problem with high-rise-lined beaches is their inflexibility. ”
— O. Pilkey & A. Cooper

Most of these heavily developed beach communities are fronted with artificial (nourished) beaches. The problem is that as the level of the sea rises, the beach nourishment sand will become less and less stable and more and more costly. The natural shoreline, unhindered by development, would be thousands of feet back and 2 or 3 feet higher than the shoreline held in place by the nourished beach. Nourished beach lifespans would rapidly decrease to the point that artificial beach construction would no longer be useful or feasible. The buildings would then have to be protected by large seawalls which would, in themselves, increase the rate of artificial beach loss.

Thus, beaches in front of the high rises will be gone. Much of the tourist industry must move elsewhere. Perhaps Cape May, New Jersey, is an example of the problem. The beach disappeared in the early 20th century as a result of placement of a large seawall. The seawall caused the problem there, not sea level rise. For most of the twentieth century, Cape May was without a beach and promenading on the top of the wall was the major beach activity.

Recife, Brazil, is an example of a beach community that has basically given up on the ocean beach but has placed a band of sand behind a large rock revetment for vacationers to feel the sand on their bare feet. Here, beach volleyball pitches have been squeezed in, as well as spaces for sunbathing. These sand pits, however, are a poor substitute for a natural beach–they have none of the protective functions of a beach, they need to be continually maintained, and they act as giant cat litters (and repositories for all sorts of other objectionable trash). This may be the future for all the high-rise-lined beaches.

Where will our main tourist beaches be when these ones disappear? What will become of all of the beach infrastructure when there is no beach? Will we learn a new way of living with beaches that allows us to co-exist? We don’t have a crystal ball, but it is our hope that high-rise-lined beaches will become a thing of the past and that we will find a new way to allow people to enjoy the beach without destroying it.

By Gary Griggs, Distinguished Professor of Earth and Planetary Sciences, Director Institute of Marine Sciences, University of California, Santa Cruz, California

While most coastlines often appear to be stable and permanent over the short time span of our visits, and some are, there are many others where the materials making up the coastal bluffs or cliffs are no match for the forces the sea exerts. Whether the constant rise and fall of the tide and the accompanying wetting and drying, heating and cooling, and exposure to salt water, or the sheer impact of breaking waves, the ocean is a challenging force to resist. Over time, the ocean always wins. In baseball terms, Mother Nature always bats last.

So while there are rock types that are very resistant to the impact of the sea, granitic and volcanic rocks, and even certain sedimentary rocks that are high in silica, being several examples, which often form the protruding headlands or points we recognize and give names to, there are others that don’t hold up so well. In addition to the rock types themselves, and differences in their cementation or hardness, there are also often structural weaknesses or irregularities that cut through or penetrate the rocks making up coastal cliff or bluffs. It is typically these weak zones, whether faults, joints, fractures or other features, which the waves seek out and erode, gradually creating tunnels, caves, or natural bridges or arches.

The coastline of Santa Cruz County has undergone some dramatic changes over the past century or so of human observation and photography, and watching the waves batter the cliffs during any winter storm makes you realize why. This is a high-energy coast with waves 10-12 feet high arriving regularly. As coastal geologists we often take measurements from old aerial photographs to see how much retreat has taken place over time and then calculate cliff retreat rates. For the much of the Santa Cruz County coastline the average annual erosion rates typically range from a few inches to about a foot/year. Cliff failure doesn’t occur in simple six inch or one-foot increments every year, however. Instead we see large slabs fall to the beach or natural bridges or arches collapse catastrophically.

The rocky coast from the city of Santa Cruz north to the old town of Davenport consists of a 30 to 75 foot high uplifted marine terrace, which has been eroded into relatively young sedimentary rocks, a mix of sandstones, siltstones and mudstones. These rocks vary in their resistance to erosion and also have been weakened over hundreds of thousands of years of stress within the San Andreas Fault system and also from exposure to waves, salt air, and gravity.

There have been a large number of picturesque natural bridges that were often photographed by earlier visitors, which preserved a permanent record for what was here and how the coastline has changed. Several years ago we published a book comparing old photographs of the Santa Cruz coast, many taken 75 to 100 years ago, with photographs we took from the same locations in 2006 (The Santa Cruz Coast-Then and Now).

“The natural bridges or arches fascinated early visitors as they do today, but the same rock weaknesses that allowed the waves to erode those arches, have also led to their demise. ”
— Gary Griggs

The natural bridges or arches fascinated early visitors as they do today, but the same rock weaknesses that allowed the waves to erode those arches, have also led to their demise. Natural Bridges State Beach is perhaps the best known and the progressive loss of two of the three bridges, one in about 1905, and the second during a storm on the night of January 10, 1980. Today only a single bridge remains.

While some natural bridges may last a century or more, others have appeared and disappeared within a few decades. One section of terraced cliff I photographed four miles north of Santa Cruz in 1969 showed a prominent point eroded into mudstone, but no arch. By 1987, an arch had formed where wave erosion had attacked a weak layer at the base of the point. By 1995 the entire arch and point had completely collapsed.

A century ago a large natural bridge spanned the entrance to cove along the coastline that formerly was a dairy farm and ranch, but today is Wilder Ranch State Park. This arch was photographed in about 1900 with not one, but two horses and buggies, perched on top of it. This wasn’t a delicate arch, but a pretty meaty natural bridge that the buggy drivers clearly had some confidence in. Based on historic aerial photographs, this grand arch collapsed somewhere between 1928 and 1943.

Closer to the city of Santa Cruz, along the oceanfront street, West Cliff Drive, there was a triple arch for a while, which was a popular site for photographs in the late 1800’s and early 1900’s. Part of this arch ultimately collapsed, leaving the famous Vue de L’eau, a picturesque single arch memorialized on many old postcards. This bridge was also known as Arch Rock and also Crown Arch (for a while it had a cap or crown of weaker terrace deposits). Lots of old photographs and postcards of Crown Arch remain, and as the years progress you can see the crown disappear, the arch gradually thin, and finally sometime in the 1920’s, it all collapsed.

The east side of Lighthouse Point, known globally as a famous surfing spot, Steamer Lane, was the site of another arch where photographs of ladies in long Victorian dresses and strange hats were often taken. A large storm in the winter of 1888 finally brought down the arch, but its base still stands in shallow water today, directly in front of the stairway where surfers heading to Steamer Lane enter the water. Lighthouse Point is now partially undermined by two separate caves, which in time will collapse, perhaps leaving new arches for the photographers of the future.

A combination of the degree of cementation or consolidation of the rocks at each of these points that provide their variable strengths and resistance to wave erosion, but internal structural weaknesses such as joints and fractures also play a role. The Natural Bridges of Santa Cruz County will continue to form and then collapse as the ocean takes its toll on the coastline.

By Gary Griggs, Distinguished Professor of Earth and Planetary Sciences, Director Institute of Marine Sciences, University of California, Santa Cruz, California

In 2001, ninety-six miles of the south coast of England along the English Channel was designated as a World Heritage Site. This picturesque stretch of cliffs and beaches extends from Exmouth on the east to Studland Bay on the west. Although it is known as the Jurassic Coast, a label with a certain appeal, it might more accurately have been named the Mesozoic Coast, as the rocks exposed span the entire 185 million years of the Mesozoic Era, including the Triassic, Jurassic and Cretaceous periods.

The fossils contained in these sedimentary rocks reveal not only how life evolved during this 185 million year period, but also record how the geography and climate changed over time. Traveling through this region in the geologic past between 250 and 65 million years ago would have revealed a diversity of environments ranging from dry deserts, lush swamps, tropical seas and dense forests, with the preserved plant and animal fossils providing the evidence for these ancient environments.

The interbedded layers of sandstone, clay, limestone and chalk exposed along the coastline contain a nearly complete history of this long span of geologic time. Along some stretches of the Jurassic Coast, these rocks have been uplifted in such a way that the individual beds or layers are steeply inclined or vertical. Walking along the shore is much like thumbing through the pages of a gigantic geology book, passing through thousands or hundreds of thousands of years with each step.

“Walking along the shore is much like thumbing through the pages of a gigantic geology book, passing through thousands or hundreds of thousands of years with each step. ”
— Gary Griggs

As sea level has risen and fall over the past several hundred thousand years, in response to global heating and cooling, waves have taken their toll on the rocks, carving a rugged coast with a vertical cliffs, arches and coves, seastacks and narrow pinnacles. The limestones and sandstones tend to be more resistant to wave attack and weathering and form vertical or very steep cliffs, such as Old Harry on the east end of the Jurassic Coast. Durdle Door is a very large arch eroded into limestone at the western end of the Heritage Coast. The rocks here are of Jurassic Age and have been tilted up so that bedding is nearly vertical with some beds being weaker than others. This has allowed wave attack to selectively remove the weak layers creating this spectacular arch.

In contrast to the harder and more resistant limestone, the clays are generally much weaker and commonly fail as large landslides (known locally as landslips), which can deliver large volumes of material to the shoreline. On May 6, 2008, a 1,300 foot long section of coastline collapsed, and was described as the largest failure in a century. Four years later, another large slip occurred at Burton Bradstock, which involved nearly 450 tons of rock, and led to a fatality. This coast does get severe weather and violent storms are common, all serving to shape and reshape this ancient coastline.

The range in rock types making up the coastal cliffs along this 96-mile long coast leads to widely different beaches. Sandy beaches occur where sandstones dominate in the cliffs, but where limestone outcrops, the beaches tend to consist of coarse pebbles and cobbles, and are quite steep.

Interesting towns and villages abound along this stretch of English coastline, among them Abbotsbury, Lyme Regis, Swanage, and Sidmouth; among the most interesting is Beer, where signs make it clear that you are, in fact, in the village of Beer.

By Gary Griggs, Distinguished Professor of Earth and Planetary Sciences, Director Institute of Marine Sciences, University of California, Santa Cruz, California

There are many strikingly regular patterns in nature that have long intrigued scientists and non-scientists alike. Beach cusps are one of these. Coastal geologists and careful beach observers or frequent visitors may have noticed these evenly spaced, semicircular, scalloped-shaped patterns along the shoreline from time to time, or perhaps not at all. These very uniform patterns seem to be far more frequent on certain beaches than others, and are much more visible from an elevated vantage point, like a cliff top or in an aerial photograph, than when standing on the beach. They can form on sand or gravel beaches and can range in width or diameter from 25 to over 200 feet, but are very uniform or strikingly regular on any particular shoreline at any point in time.

The cusp spacing is shorter in gravel beaches and longer on finer-grained sandy beaches. These very symmetrical features are far easier to recognize and appreciate, however, than to figure out or understand, and we could just leave it at that and appreciate them for their symmetry. But being curious scientists, we usually look for answers to the mysteries we find in nature.

Published writing on these features goes back nearly a century to 1919 when one of the first coastal geomorphologists, Douglas Johnson, described these unique landforms.

“There are many strikingly regular patterns in nature that have long intrigued scientists and non-scientists alike. Beach cusps are one of these. ”
— Gary Griggs

Beach cusps seem to form most often when waves approach normal or at a right angle to the shoreline. The portion of the broken wave that washes up the beach face is called the swash, and the maximum difference in the run-up of the swash seems to be the dominant influence on the spacing of the cusps.

There have been two prevailing ideas on the formation of these symmetrical shoreline features, although neither is easy to explain and both probably will leave some lingering doubts in the minds of most readers. The earliest idea on the formation of cusps was that they were due to distinct properties of the waves breaking on the shoreline and were, therefore, essentially imposed on the beach by nearshore wave interactions.

In recent years, however, this theory has been essentially displaced by another idea, which involves the somewhat complicated concept known as self-organization. This principle, which has now been reproduced in models, shows that interactions between wave runup on a beach and sediment transport can combine to give rise to instability that soon produces cusps. On a flat beach, areas will develop that have slightly lower relief or elevation than adjacent areas. As waves wash up the beach, they will accelerate or speed up over these lower areas, and cause erosion. These lower areas will deepen gradually to form an embayment. On the other hand, those areas on the beach that are slightly higher will slow down the uprush of the waves, causing sediment to be deposited on top of them. These will evolve to form the horns between the embayments, and together they known as beach cusps.

Somehow, as these cusps begin to form, and they can develop quite quickly as wave conditions along the shoreline change, these features interact or communicate. As a result the patterns of erosion and deposition along the beach face (the cusps) begin to develop a very uniform size and spacing as the beach tries to rearrange itself through erosion and deposition to reduce variations along its surface.

This self-organization process, at least for now, is the favored mechanism used to explain the formation of these widespread and interesting shoreline features. They occur in both small pocket beaches but also may extend for miles down the beach, and can then disappear within a few hours as wave conditions change. Beach cusps are one of those somewhat mysterious natural phenomena that for most of us may simply be best appreciated without trying to completely understand just how they form.

By Orrin H. Pilkey and Norma Longo, Nicholas School of the Environment, Duke University, Durham, North Carolina

Presque Isle in Lake Erie (one of the U.S. Great Lakes), Pennsylvania, is a recurved sand spit with seven miles of shoreline facing the open lake. The width of the spit ranges from 20 to 30 meters at the narrow neck where it connects to the mainland to as much as a mile near Gull Point. There is a dominant longshore drift along the length of the spit from its neck toward the northeast. The spit (peninsula) probably originated as a glacial moraine but its present-day surficial character and evolution are entirely related to lake processes. The peninsula, with its wide variety of wildlife, its forests, marshes, ponds, dunes, and beaches, surrounds Presque Isle Bay and protects the Erie harbor.

Presque Isle is a widely used Pennsylvania state park and also a National Natural Landmark, a designation that is one step below a national park. As many as 4 million visitors enjoy the beautiful park each year, in all seasons, for a variety of activities that include hiking, bird watching, skiing, and fun at the beaches. At Presque Isle, the public continues to take advantage of the only “seashore” in Pennsylvania and enjoy its varied and picturesque landscapes. At the northeastern tip of the peninsula is Gull Point which was once a 200-acre forested area with large wetlands. The Point is an unusual area with a unique succession of plant life, ranging from a sandy, freshwater environment to a climax forest, all within a few hundred yards.

The beaches along the peninsula consist of a wide variety of grain sizes ranging from fine to coarse quartz and lithic sands and small pebbles. The spit was subjected to minor erosion, although the senior author of this article observed that occasional overwash by storm waves crossing the highway and flooding parking lots was considered to be a major problem. Shoreline erosion seemed to be a less important factor. Groins and seawalls had previously been installed in some places along the spit, but beach replenishment has been the mainstay of erosion control since the 1950s. But, when minor erosion occurred along the entire spit, government and public entities debated a variety of possible solutions to the perceived problem.

The preservation of Gull Point was a central issue in the contentious public debate which went on for more than a decade.

Possible solutions considered included:

The segmented offshore breakwater solution was chosen by the U.S. Army Corps of Engineers (USACE), Buffalo District, and the breakwaters were completed in 1992. In total, 55 boulder breakwaters were built, each 150-feet long, parallel to the shoreline and separated from one another by 350 feet. Total cost in 1992 dollars was around $30 million.

“Each year approximately 55,000 tons of additional sand are needed to offset impacts of annual erosion. ”
— O. Pilkey & N. Longo

The Corps of Engineers claimed that the segmented breakwater idea was a passive, permeable, non-intrusive, and permanent solution to the erosion problem. From an environmental standpoint, the most important design assumption was that sand would flow behind the breakwaters toward the tip of the spit and thus preserve the forest and wetlands. In 1978, the Corps had constructed three experimental breakwaters to test whether sand would flow behind them. Instead, these breakwaters halted most of the sand flow and caused immediate severe downdrift erosion which the Corps attributed to a storm rather than to a fundamental problem with the breakwater design (which it was). Even the Corps’ Coastal Engineering Research Center supported the impossible conclusion of continuous flow of sand behind the breakwaters. Immediately after the construction of the breakwaters, Gull Point began to erode rapidly because of the loss of sand.

Before the 55 breakwaters were emplaced, the Moffatt and Nichol consulting firm said the project would not work as the design of the project was faulty and sand would not flow behind the breakwaters. Clearly the flow of sand behind the breakwaters was a scientific impossibility because wave patterns are unpredictable. It was clear that the offshore breakwaters were a “done deal” as far as local and state politicians were concerned. The negative consultant report and even the failed experimental breakwaters had no impact on the decision to go ahead with the project.

Offshore breakwaters rarely allow sand transport behind them. Breakwaters are designed for a certain local wave type coming from a certain direction. If the waves were always the same type coming from the same direction, sand transport could occur behind the structures if they are spaced correctly. But nature is never uniform and predictable, and wave conditions vary. As a result, sand doesn’t flow along the shore but builds up between the beach and the breakwaters, forming tombolos. The tombolos on Presque Isle are removed periodically and the sand is placed on the beaches, a form of beach replenishment. The Corps states that the beach is annually nourished with stockpiled sand or sand dredged from an offshore source. Each year approximately 55,000 tons of additional sand are needed to offset impacts of annual erosion.

Since before the installation of the breakwaters, beach replenishment has provided fine swimming beaches that the park regularly grooms to keep them smooth and debris-free. Early in 2016, the Presque Isle State Park beaches placed first in the “Best Freshwater Beach” category of nationwide, online voting in a travel award contest sponsored by USA TODAY.

After the breakwaters were constructed, the Corps of Engineers received several awards for the project from a number of organizations. These included the Michigan Society of Professional Engineers, the American Society of Professional Engineers, and the American Shore and Beach Preservation Association (ASBPA). The bottom line is that more than 20 years after the offshore breakwaters were constructed, their success was determined without considering the original assumptions of the project design, the most important of which was the promised preservation of the forest at Gull Point. Ignoring original assumptions and declaring success means that nothing was learned from the failures of the offshore breakwater project.

The Gull Point shoreline beyond the last breakwater has retreated more than 500 feet since 1992. The sand eroded from Gull Point has extended the very tip of the spit and added more than 5 acres of land area, but this is not the treasured original wetland-forest environment. Instead, it is a large sandbar with little vegetation. It is anticipated now that an inlet will form where the Gull Point forest once existed and the point will become an island. In the meantime, annual replenishment is required to maintain the beaches, but this sand contribution has not helped to preserve Gull Point.

Erosion along the shore continues. Park Guide 21 for Presque Isle notes that even though Lake Erie rarely freezes all the way across, ice forms along the shore during most winters. Due to warmer weather conditions, less sea ice forms. The U.S. Army Corps of Engineers reported in April 2016 that “this year, due to the lack of protective ice cover, the beach was exposed to battering wave action throughout the winter. As a result, significant erosion has occurred along the length of Presque Isle” (DredgingToday.com). This bears a resemblance to situations along Arctic shorelines, for example, the Alaskan villages of Shishmaref and Kivalina, and many other small Arctic villages in Siberia, the north slope of Alaska, and northern Canada. In these places, sea ice no longer forms in September but forms much later, in November. The late freeze-over exposes beaches to the fall storm season, leading to increased erosion.

There are two important lessons to be learned from the failure of the breakwater project.

Further Reading:

• Brady, Terry. “Presque Isle State Park Beaches Place First in National Competition.” Pennsylvania Department of Conservation and Natural Resources. March 23, 2016.
• Delano, Helen L., Pennsylvania Geological Survey, Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey. 1991. “Presque Isle State Park, Erie County: A Dynamic Interface of Water and Land.” Pennsylvania Trail of Geology, Park Guide 21.
• DredgingToday.com. Posted April 6, 2016. “USACE: Presque Isle Beach Faces Significant Erosion.”
• Fatica, Alex. “God’s beautiful gift, close to home.” Spring 2009. Pennsylvania Center for the Book.
• Gorecki, Richard J., and Joan Pope. August 1993. “Coastal Geologic and Engineering History of Presque Isle Peninsula, Pennsylvania.” U.S. Army Corps of Engineers, Waterways Experiment Station. Miscellaneous Paper CERC-93-8. 100 p.
• Massing, Dana. Erie Times-News, April 6, 2016.
• Millette, Christopher. “Presque Isle beaches open after sand replenishment.” Erie Times-News, July 17, 2014.
• Nummedal, Dag. 1983. “Sediment transport and morphodynamics of the Presque Isle shoreface.” Technical Report No. 83-1, Louisiana State University, Baton Rouge, LA.
• Pilkey, Orrin H. 2012. “Presque Isle Breakwaters: Successful Failures?” in J.A.G. Cooper and O.H. Pilkey (eds.), Pitfalls of Shoreline Stabilization: Selected Case Studies, Coastal Research Library 3, DOI 10.1007/978-94-007-4123-2_9, Springer Science_Business Media Dordrecht. p. 131-139.
• Pilkey, Orrin. H., and Katharine L. Dixon. 1996. “Presque Isle: The End of a Beach,” in The Corps and the Shore. Washington, D.C., Island Press. p.145-171.

By Gary Griggs, Distinguished Professor of Earth and Planetary Sciences, Director Institute of Marine Sciences, University of California, Santa Cruz, California

California has over 300 miles of beaches, those that most residents and visitors think about are the ones consisting of find-grained white sand, whether Santa Monica, San Diego, Santa Barbara or Carmel. But there are also some interesting anomalies. One of California’s strangest beaches sits 30 miles south of the picturesque north coast town of Mendocino and just 3 miles south of Point Arena along Highway 1. At low tide, Bowling Ball Beach is covered with hundreds of 3- to 4-foot diameter, round, sandstone concretions that look like massive bowling balls that have collected on the beach.

Concretions are hard, often spherical or rounded masses of sedimentary rock formed when a mineral cement, often silica or calcium carbonate, fills the spaces between individual grains. These structures typically form around some hard object, a shell, pebble, or even a bone or tooth, after the sediment has been deposited but before it has completely hardened to rock. Because of the cement, concretions are nearly always harder than the surrounding sedimentary rock and therefore typically remain behind when the surrounding material is weathered or eroded away.

The cliffs backing Bowling Ball Beach consists of sandstone and shale that has been uplifted and now tilt at very steep angles down towards the shoreline. The sandstone tends to be harder and more resistant to erosion than the shale, such that the harder sandstone layers extend across the intertidal zone as ridges, giving the very wide wave-cut platform a corduroy appearance at low tide.

“The steeply dipping cliffs are nearly as interesting as the bowling balls themselves and create what have been called flatirons.”
— Gary Griggs

Many of these large round concretions have been eroded out of or are still attached to the sedimentary rocks exposed on the intertidal platform. Solution from immersion in seawater and wave action over time has gradually detached many of these boulders, which have been moved around and now are concentrated in the bedrock grooves or troughs that have been eroded into the upturned rocks, much like bowling balls in the gutter of a bowling alley. Other concretions appear to have been dislodged from the adjacent cliffs by the processes of rainfall and runoff, and then have rolled down to the beach and been moved around by wave action.

The beach is accessible from California State Highway 1 and is part of the Schooner Gulch State Beach. A trail leads north from a parking area down to the beach. But you need to make sure you plan your visit at low tide to best observe the bowling balls. It’s a little hike, but well worth the effort. For the less adventurous, or if you don’t have the hour to hike down to the beach, you can also stop on Highway 1, directly across from a small country road (Bill Owens Road) and at low tide, get a good view from the top of the steep cliff.

The steeply dipping cliffs are nearly as interesting as the bowling balls themselves and create what have been called flatirons. Similar rocks are exposed at the base of the Santa Ynez Mountains along the northern Santa Barbara County coast near Gaviota Pass, and also in the mountains above Boulder, Colorado, which are actually referred to as the Flatirons.

Large spherical concretions nearly identical to those at Bowling Ball Beach occur in the cliffs and along the beach on the Otago coast of the South Island of New Zealand between Moeraki and Hampden. The Moeraki Boulders are about the same size of those along California’s Mendocino coast, and have weathered out of the mudstone bedrock. They are cemented by the mineral calcite, which makes them more resistant than the surrounding rock. Geologically, these rocks are of Paleocene age or about 60 million years old.

Nearly identical spherical concretions, known as the Koutu Boulders are found in the cliffs and on the beaches of the shoreline of Hokianga Harbor, on the North Island, New Zealand, between Koutu and Kauwhare points. Some of these are up to 10 feet in diameter, but again, low tide is the best time to visit.

J. Andrew G. Cooper, University of Ulster, Coleraine, Northern Ireland and Orrin H. Pilkey, Duke University, Durham, NC, USA

Gabon is on the equatorial coast of West Africa (Figure 1) between the Congo and Niger deltas, surrounded by Equatorial Guinea and Cameroon to the north and Congo to the south and east. Gabon has a long, sandy coast backed in most cases by a dense tropical rainforest.

The density of the forest makes the beach a handy thoroughfare for the large animals that dwell in the forest. Footprints and other traces (e.g., elephant dung) of wild animals can frequently be seen on the beach. Elephants, buffalos, various antelopes, monkeys, pythons and even leopards leave their trails on the beach. Seeing the animals themselves is, however, less common as they probably travel by night, the time when being on the beach could be dangerous to people.

Elephants, the largest of the animals at the Pongara shoreline, are a separate species, distinguishable from elephants in interior Africa by their slightly smaller size and different tusk pattern. These forest elephants come to the beach in the early mornings and at dusk. (Figure 2) Perhaps this is done to consume some favored plant in the zone of salt spray. Trampled small trees next to the beach provide evidence of their eating habits (Figure 3). Hippos are rare here but they are known to frolic in the salt water, an activity avoided by elephants.

“Elephants, buffalos, various antelopes, monkeys, pythons and even leopards leave their trails on the beach… ”
— A.Cooper & O.Pilkey

This Beach of the Month report emphasizes the beaches at the Pongara Beach resort in the Pongara National Park located across the Gabon Estuary just south of the capital city, Libreville. Gabon is not on most international tourist maps. Most of the visitors to the resort at Pongara are Gabonese. The wild animals, beautiful beaches, and closeness to nature (Figure 4) are, however, good reasons to visit beaches in Gabon’s national parks. One problem facing beach tourism in Gabon, however, is the very poor quality of the roads leading to many beaches (Figure 5).

Getting to the Pongara Lodge is an adventure in itself. A 45- minute boat ride across the Gabon Estuary and into the open Atlantic Ocean terminates offshore of the lodge where there is no pier or dock. Visitors and their luggage are transferred carefully and in small numbers onto a tiny boat with wheels that runs ashore and is pushed up the beach by 4 men waiting hip-deep in the surf zone. The process, requiring skillful timing to cross the surf zone, ensures that visitors arrive without as much as a splash of water.

The light yellow-brown sandy beach runs for many kilometres, interspersed with occasional headlands of well-lithified Cretaceous rocks that form low cliffs. Grain size of the intertidal beach is well-sorted, medium sand with strikingly small amounts of shell material larger than sand size. Shell lags are rare and consist of small shells only. Concentrations of heavy minerals (black sand) are common. The heavies are responsible for a number of colorful beach surface features including rings (Figure 6).

Wave energy is low and often the waves don’t even break before they reach the shore. Instead they swash up the beach which has a very steep upper profile. At low tide, a flat sandy terrace is often present. There is little evidence of big storms and significant storm surges impacting on the beach. The lack of storm deposits is characteristic of shorelines near the equator. Backing the beach is usually a small sandy ridge with relief of less than 5 feet and no evidence of extensive overwash penetration into the rain forest. The major exception to this is the incursion of sand (and logs) at small river mouths.

Soft (bubbly) sand is (Figure 7) ubiquitous on the uppermost beach, making walking difficult at high tide. Walking is further complicated by accumulations of logs on the beach, which require stepping over or around. The soft sand is due to cavities formed in the sand by air pushed up by a rising tide. Equally ubiquitous is barking sand which is often found when the sand is well-sorted and without shells. Dog Island, Florida, beaches also exhibit widespread barking and, like the beaches of Pongara Park, are fine-to-medium well-sorted sand with little calcareous material.

The source of sand on Gabon’s beaches is likely sand deposited on the continental shelf during lower sea levels. It is clean and well-sorted, unlike fluvial sands, but it is likely that the sand supply from rivers to northern Gabon beaches is high. One indication of this is the paucity of sea shells on the beaches, possibly indicating that the shell content is being diluted by terrigenous sediments being contributed to the beaches at the present time.

Everywhere in northern Gabon the coastline is eroding (Figure 8). Trees falling into the surf are clear evidence of long-term erosion, and along the Pangora ocean shoreline this is in the absence of engineering shoreline stabilization structures such as groins or seawalls that cause erosion elsewhere in Gabon.

A feature everywhere on Gabon’s beaches is the abundance of huge logs exhibiting flat-sawed ends (Figure 9). Broken free from rafts as they are floated downstream from the interior forests, thousands of these by-products of the country’s logging industry form an important part of almost every beach, including those of Pongara National Park. (Figure 10) They are usually washed up and deposited near the uppermost beach, but they frequently are covered and uncovered by sand and occasionally repositioned. Interestingly, we saw no floating logs off any of the beaches we visited.

Over a three-day period at Pongara Lodge, a 6-ft-long woody stump protruding from the sand on the bathing beach was revealed to be a 50-ft log, as the beach level lowered. The highly dynamic nature of the beaches is somewhat at odds with the lack of storm evidence, but the waves approach consistently from the southwest at quite an angle to the shoreline, so longshore drift is active on the steep beachface. The logs act as impromptu and flexible seawalls, but they shift landwards as the coast retreats. Virtually the entire shoreline here is eroding at what appears to be a slow rate.

“In contrast to the beaches in Pongara National Park, the beaches on the north side of the Gabon Estuary and on the adjacent open-ocean beaches are strewn heavily with plastic. ”
— A.Cooper & O.Pilkey

Unfortunately plastic is another ever-present component of the uppermost beach here. In the park, the plastic is mostly made up of drinking water containers. Plastic debris is unevenly distributed (Figures 11a, 11b) but as a rule, although it is widespread, only small amounts are present. This is in stark contrast to beaches near Libreville which are covered in domestic waste.

The Libreville shoreline on the north side of the Gabon Estuary is a different story. Wherever there is property near the beach (Figure 12), one finds makeshift seawalls made of laterite boulders (Figure 13). Laterite is a rusty red rock, found in warm tropical climates. It is formed by the gradual long-term weathering of the underlying soil and rock. The lines of red boulders are found on almost every beach we visited that had some sort of development adjacent to it (Figure 14). As a result, at high tide most beaches are narrow or absent altogether. Many of the walls are used to stabilize the shoreline in front of a single structure (Figure 15) such as a small store or restaurant, thus creating erosion problems on adjacent shorelines.

Mining of beach sand has likely been the source of sand for the widespread concrete construction. We observed several dump trucks full of beach sand heading for Libreville.(Figure 16)

Virtually the only swimming beach in Gabon used by large numbers of people is in Libreville (Figure 17). We were informed that swimming and beach strolling by local people has only been important in the last decade or two. Outside of Libreville we saw only occasional swimmers on the beach, usually children.

In contrast to the beaches in Pongara National Park, the beaches on the north side of the Gabon Estuary and on the adjacent open-ocean beaches are strewn heavily with plastic. In front of remote restaurants/bars, the beaches appear to be regularly raked and the plastic gathered in piles. It seems that the piles must wait a long while before being removed (if ever). Within the city of Libreville, the plastic trash on many beaches is of extraordinary proportions (Figure 18), especially near the mouths of small streams. Clearly such massive amounts of plastic and other refuse on Libreville’s beaches not only destroy any beach tourism but must significantly add to the apparent pollution problem on the beach and in nearshore waters.