geography

 

For a small island, Roatan’s geography is amazingly diverse. At nearly 50 km (31 mi) long, less than 8 km (5 mi) wide at its widest and reaching elevations of 244 m (800 ft), visitors will experience everything from flat sandy beaches, rocky, volcanic rock shores, mangrove forests, lush valleys and steep rainforest-covered hilltops.  Sitting at the southern terminus of the Mesoamerican Barrier Reef System, the island is surrounded by coral reefs, protecting it from the open ocean and is home to a complex underwater ecosystem.

bay_islands_-_roatan

 

A Brief Description

Roatan is the largest of the Bay Islands and has some of the greatest beaches in the Caribbean including West End Bay, with its magnificent turquoise waters, a favourite haunt of international divers. Although best developed, Roatan is still mostly wilderness. Its Northern reef is very massive and forms a barrier and an inner lagoon between the reef and the island. This reef is bisected by about half a dozen cuts that lead to bays scalloped along the coast. The bays and the few offshore islets form truly breathtaking scenery.

The outside of the reef is a continuous wall that typically begins in shallow water and descents to a 45 degree coral talus and sand slope at about 110 feet. Sometimes the wall plummets to unseen depths. Caves, crevices, overhangs, natural cathedrals, fissures, caverns and protrusions are constant features of the Northern reefs. Roatan's southern side harbours a fringing reef formation, generally closer to shore than the northern reefs and nearly as continuous. Shallow areas provide snorkelling and scuba sites featuring coral gardens knitted by huge stands of Elkhorn coral. Deep sites begin shallow and fall directly to a shelf or the abyss below.   Large Pelagic fish are occasionally sighted both sides of Roatan.

 

What Happened Here?

How did this fantastic geological formation come to be, what geological events took place and when did they occur?   Millions of years ago, giant tectonic plates scraped against one another in titanic clash resulting in the underwater mountain range today we call the ‘Bonacca Ridge’ in which the Bay Islands are now found.  The upwelling of magma and the crumbling of basalt rock (the core of the islands) built, over millennia, a mountain range whose peaks manage to barely extend above sea level forming the Bay Islands.   Over time these islands have become covered in thick tropical vegetation, a variety of animals and eventually a civilization that have come to know them as the Islas de la Bahía or in English, the Bay Islands.

 

Local Beliefs

Local opinions differ and suggest several explanations for the formation of the Bay Islands, ranging from volcanic eruption to sections of the mainland that have broken free and just floated away.  Although technically these theories are incorrect, in a way both of them do lend themselves to the actual formation of the island chain.  South and running parallel to the Bonacca ridge lies the Motagua Swan Islands Fault, a meeting place of tectonic plates.  This ridge extends underwater from mainland Honduras and thus, the theory that we are in fact a piece of the mainland is in part, true. The geological structure and bedrock of the Bay Islands, as far as rock composition, is strikingly similar to that of the Honduran and Guatemalan mainland.  Thus, we are part of the same continental crust and come from the same roots as mainland Honduras and Guatemala.

 

Modern Interpretation

Geologists estimate that the islands emerged from the sea primarily in the Eocene and Oligocene time periods, or roughly between 56-34 and 34-23 million years ago.   The mountains were formed and lifted out of the sea by an upwelling of magma via the separation and parallel movement of the Motagua and Swan Islands fault. The Bonacca ridge is a Horst which is a type of geological formation of up thrown blocks bounded on either side by normal faulting, which continue to grow today albeit very slowly.   The faults continue to move and change the geological structure of the islands at a continuous rate, called the slip rate. Some of the faults are locked together by friction causing a build up of tension, which when released suddenly, results in an earthquake.   Earthquakes are most often a destructive force but ironically can also be a productive one as well.   post-glacial_sea_level

Evidence of earthquakes that have caused the sudden uplifting of the Bay Islands can be seen throughout the Bay Islands, including uplifted and warped landforms on the western part of Roatan that come from prehistoric earthquakes of magnitude 7 or greater. This uplifting, that continues to cause Roatan's unique geological structure, comes from a subsidiary fault to the Swan Islands fault called the Flowers Bay Fault, a familiar name to any local. 

‘Tectonic’ and ‘volcanic’ forces are not the only ones that have had a hand sculpting Roatan and the surrounding Bay Islands; sea level has also changed over geologic time.  As the graph above shows, sea level today is very near the lowest level ever attained, the lowest level occurred at the Permian-Triassic boundary about 250 million years ago.   During the most recent ice age, which was at its maximum some 20,000 years ago,  the world's sea level was about 130 m lower than it is today.  This was principally due to the large amount of sea water that had evaporated and been deposited as snow and ice, mostly in the Laurentide ice sheet. The majority of this snow and ice had melted by roughly 10,000 years ago.


A Diamond in the Rough

During this period while the sea level was lower, Roatan must have been a spectacularly different place than it is today.  Roatan would have been surrounded by a stepped series of cliffs with waterfalls cascading into the sea some 130m below.  Remnants of these ancient waterfalls can be seen by divers today at dive sites such as ‘Peter’s Place’ and many others.  During this time water cut many other features into the areas above the cliffs adjacent to what is now the shore and these features, now in relatively shallow water, can be enjoyed by divers of all ability as amazing features to dive through and explore.

This unique set of random geological forces has transpired to create a truly wondrous place to experience and we are left with the scattered jewels known to the locals as the Islas de la Bahía.

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