The Geography and Geology of Roatan
The Honduran Bay Islands (Las Islas de la Bahia) are comprised of eight islands and more than 60 cays resting on the Bonacca Ridge, which is about 40 miles northeast of the north coast of Honduras. They are beautiful Caribbean islands which still have a lot of old world charm, although development is increasingly becoming apparent. Visiting these islands will leave you with little idea of what Honduras as a country is like since they suffer from few of the problems seen on the mainland, simply because tourism brings plenty of Dollars to the local economy.
The islands are surrounded by a reef system, which is part of the second largest reef system in the world. At times the reef is only a short swim away from the shoreline. The reef is one of the most species-rich waters in the Caribbean in terms of both coral and fish.
Roatan is long and narrow, let's say 5 x 37 miles. Some places, much narrower; the length is debatable as the far NE end is rather swampy.
Roatan runs Southwest to Northeast, at an angle. It is usually printed on a map or displayed horizontally, causing "North" to be skewed off to the 2 O'Clock position, making most maps very confusing.
The centerline of the island is a backbone ridge line that runs as high as about 600 feet (I'm too lazy to look at my maps). Roatan and the Bay islands are part of the Bonacca ridge line, a volcanic remnant that still has snaps and cracks, often heard underwater, at a usual epicenter some 30 miles to the North.
This ridge line does not divide the island in half, equally. Nature rarely works that way.
When one drives from the Airport, you hardly notice the gentle easy ascent as you drive from the South to North. As you crest the ridge, most anyone will note the more obvious steeper drop ahead.
This ridge line runs quite a bit closer to the Northern half of the island. As the land descends to the North, it does so (comparatively to the South) rather steeply. This steepness also continues at the Ocean, causing the underwater geography to be shaped in a similar manner.
For millions of years, the heavy storms have come at Roatan from the North. This is what has caused the shape of both above and below water Roatan. When heavy "North-ers" arrive (Dec-Mar) or during tropical storm season (Aug-Nov), if the island is getting winds, you will immediately note the salt smell from the crashing surf as you crest over the ridge line from the South.
Roatan is largely out of the historical Hurricane track. It is a rain forest island, which we used to call jungles.
The distance from the ridge line to the South shore is much longer. The Southern shoreline is comparatively at the end of a slower and more gentle descent. The Southern shore is where you will find more mangrove growth.
The Southern geography continues on this gentle slope into the ocean, but only for a short while. Not many feet offshore, running from Coxen Hole to Port Royal, are a series of shallow reef coral heads that start in 5-30 feet and drop to a first sandy shelf in 90 feet. From there on, and very quickly, you can get in 3000 feet of water in a blink. There is very little current flow, so visibility can be degraded after a storm (remember those eons of heavy Northerly storms that blow the soil over the ridge line to rest on the Southern slope). The island lies in a position that causes 10+ hours of sunlight a day to fall directly upon exposed, shallow South side reef structures. This causes a lot of florid growth and the microscopic nature of this area. Essentially, for that very reason- limited visibility is not that much of an issue there.
Northern/Western reefs are quite a bit different. The waters there are generally much clearer, dues to the much quicker flow of water and the lack of mangroves (and extant soil deposits). The reef heads start much further offshore and they begin deeper. There is a running underwater plateau along much of the North & West, 90~115 feet from my fading memory.
The darker slopes of the Northside lend themselves to a much more dense vegetation with a lot more vegetable matter on the jungle floor. The South side is widely cultivated and the vegetation is more sparse and concentrated. Island development has occurred along the shoreline of the North and West, with the major landholders of the island declining to sell off much territory along the South shore.
Is the diving better off of one side or the other? Not really, it's just different.
The North side is typical of the diving that one used to be able to find all over the Caribbean. A cresting reef followed by a sloping plateau 20-60 feet deep and then a sudden drop off to thousands of feet, creating a beautiful wall and stunning geological features. Larger predatory fish can often be seen at some of the most popular dive sites, due in part to the prevailing currents bringing nutrient-rich water, and also the fish feeding activities of some dive operators.
The South side is for those divers who love the macro life that can be found in expansive soft coral gardens. it rewards the slow and observant divers with better buoyancy skills. You have to be able to hover and get in close to see all of the many micro/macro critters that use the shallow reef structure as an incubator and niche hiding spot.