SAN SALVADOR ISLAND, BAHAMAS
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Observations and comments by: John
I. Garver Document can be located from: http://idol.union.edu/~garverj/Geo35/hurricane/Damage.htm |
Toppled Acropora Palmata in the backreef at French Bay
INTRODUCTION
In October 1996, Hurricane Lili, passed directly over the island of San Salvador, in the eastern Bahamas with winds over 100 MPH. Eyewitness accounts suggest that the entire storm lasted about three hours with only a brief interlude when the eye was directly over the Island. Many researchers and field trip leaders who bring students to the Bahamian Field Station are, of course, interested in the aftermath. This short note is for those researchers and educators that have visited or will visit the Island. The photos are high quality (i.e. big) so you will need to have a fast connection to get through this in a reasonable time. Note that the Bahamian Field Station suffered only minor damage which is almost completely cleaned up at this time. Recent visitors will notice a few less trees and a new roof on the Snack Bar.
This account of the effects of hurricane Lili is based on a week of observation of the natural environment on San Salvador Island from 1 Dec to 7 Dec, 1996, about 1.25 months after Hurricane Lili hit the Island. In this short note, I mainly focus on the geologic effects of Hurricane Lili. Islanders will presumably give you a very different tale because there was considerable loss of property - especially roofs in Victoria Hill Settlement and Cockburn Town. United Estates, as well as the eastern part of the island, received very little damage.
GENERAL OBSERVATIONS
In general, it was surprising how little damage there was to the beaches, reefs, etc. However, after looking in detail some general patterns and important points became clear.
· Most extensive damage was on the west side of the island.
· Almost no damage on east side of the island.
· It seems that the most significant surge was on the southwest side of the island.
· Extensive tree damage at high elevations.
· Generally little evidence of major sediment transport from beaches.
· Scattered damage to living coral.
· Extensive garbage in and around reefs in Fernandez Bay (esp. Monument).
· Several major washovers in and around French Bay and the Gulf.
· Destruction of the cabana at Grotto.
· Destruction of the public dock at French Bay.
· Extensive salt burn and wind damage to vegetation on western side of island.
HURRICANE TRACK AND INTENSITY
Lili was spawned late in the season in the northwestern Caribbean Sea and tracked to the northeast. Notable landfall was in Cuba, and, of course San Salvador Island in the Bahamas. On the Island, I talked to one local resident who had lived there all her life, and she likened the hurricane to Donna in 1965 - one of only several major events in the recent history of the Island. The data below suggest that during the landfall of Lili across the eastern Bahamas, winds were between 105 and 110 MPH (~169 to 177 KPH).
Track of Hurricane Lili, from FSU hurricane site, who credits Purdue Univeristy for this image
Tracking data and intensity with time are available on the internet. These data show that the storm was most intense over the eastern Bahamas and western Atlantic. Shown below is part of the tracking data from the Hurricane forecast at Florida State University.
Data below include: Date; time; latitude; longitude; pressure; and wind speed.
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17. OCT19/09UTC
23.9N 75.1W 969MB 105MPH |
Swath of intensity associated with Hurricane Lili, from FSU hurricane site - derived from National Weather Service and National Hurricane Center, NOAA. ORANGE represents tropical storm intensity, RED represent Hurricane force winds (select this image for a larger version).
PHOTOGRAPHS OF THE EFFECTS OF LILI
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Please start with the
Satellite overview (175k) of this presentation - this satellite
image of the island shows the principal focus (and location) of the
photos that follow. The following descriptions below (A-F) are shown
on this location photo. The location of the a variety of features in
the eastern French Bay area are shown in the map
of eastern French Bay. |
[A] SEVERE DAMAGE TO TREES AT HIGH ELEVATIONS
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On the western side of the island, it seems as though most large trees were stripped on many of there leaves and branches. In some cases the destruction to the trees was almost complete, especially those areas at higher elevations. Leaf litter and branches are ubiquitous making routine travel down common paths difficult. For example, the path to Lighthouse cave was almost impassable, but it has since been cleared. |
In this close up of the same photo (297K) (A2) , you can clearly see the ridges of trees stripped of all of their leaves (labeled "A"). Virtually all of these trees are on the top of the highest elevation in this area.
Farther south, many of you will be disappointed to hear (and see) that the tree in Owls hole (A3) - an important karst feature on the island - suffered severe damage and I would be surprised if it lives.
[B] EXTENSIVE SALT-SPRAY AND WIND DAMAGE
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All along the east side of the island (especially along Fernandez Bay and around Victoria Hill Settlement) much of the vegetation along the road and beaches has been killed by either sea salt or wind. Although this damage is not very photogenic, a couple of shots here illustrate the damage. |
This photo (B2) is from the road near the turnoff to Grotto Bay . Note that the cabana is gone - it got knocked over, but the entire area was cleaned up in early December (1996). Also note in the foreground many of the bushes have been killed.
This photo (B3) shows a general scene along the beach side roads. Note that although many trees are standing, they lack leaves.
[C] CORAL DAMAGE
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In general it seems that, coral damage was not
widespread. It was clear, however, that locally some of the more branching
forms were damaged, especially A. palmata. It appears that the reefs
on the south side of the island (French Bay) and small patch reefs on
the west side of the island (e.g. Monument, Lindsey, etc.) were the
worst hit. I would unofficially estimate that even in those cases, less
than 5% of the reef was damaged. In general, when snorkeling on these
reefs you not think anything was different unless someone told you to
look for damage. |
· On the reef flat and the reef crest, sea fans (Gorgonia sp.) (C1) had been ripped up and washed into the back reef - they are common in the backreef rubble and beyond in the backreef lagoon and on the beaches. In this photo, you cannot see any hurricane damage, but it is from here where many of the Sea Fans were ripped up and deposited in the backreef area (behind the swimmer). The location of this part of the French Bay reef is shown in the map of eastern French Bay.
· Most of the reef rubble (165K) (C2) , however, contained virtually no freshly killed pieces of coral, only a few Gorgonia sp. In this photo, all of the coral fragments are encrusted with calcareous algae and were presumably killed before Lili hit the Island.
· The damage to the reef was most apparent in French Bay where toppled Acropora palmata could be found. (149k) (C3) It appears that this large A. palmata was completely flipped over. The calcareous encrusted underside is now facing upwards. Note the freshly broken branches in the lower left - these are shown in detail in the next photo.
· Here, another picture shows a close-up of the Acropora palmata tipped over in C3 (182K) (C4) showing the freshly broken branches.
[D] CORAL RUBBLE WASHOVER & BEACH EROSION
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At the east end of French Bay, surge brought coral rubble and water into small standing bodies of water ("swamp" on the San Sal topographic map - see map below). The water level was high enough that it crossed the road. Beach erosion was extensive along the southern side of the island (French Bay). Although sand had clearly moved around at Southwest Point, the beach there looked 'normal' except that almost all of the vegetation and trees are either gone or stripped bare at the parking area which is in the dune complex. Sand transport and beach erosion along Fernandez bay didn't seem out of the ordinary except near Telephone Pole where there was more exposed bedrock then I remember. |
This photo shows students wading through the pond to get to the deposits (D1). During the storm, the water level would have been to their shoulders. In this picture, the deposits are faintly visible on the other side of the pond. The location of these deposits is shown in the map of eastern French Bay.
Sea Fans (Gorgonia sp.) washed over the rubble, past the pond (D1 above) and onto the road (D2). Water would have been a little less than waist deep during the storm. You can see the pond in the background. Behind the pond is the rubble deposit of coral from storms. New coral was added to this rubble deposit during hurricane Lili. This picture is looking to the west, and was taken along the road.
Storm waves caused extensive beach erosion along French Bay (D3), has left wonderful exposures of the modern beach and dune complex. Surge deposits from the storm are above this line of erosion in the bushes.
Storm waves caused severe beach erosion in and around the Public Dock (D4) at French bay and resulted in its destruction. All of the boards of the dock, some and the pilings, and part of the road has been washed away.
Locally, high-energy waves rip up bedrock and toss it onshore. These bedrock-rubble deposits are common in two places: the Gulf (southern tip of the Island) and Grotto Bay. Here you can see bedrock rubble deposits at Grotto Beach (D4). These rubble deposits existed before Lili, but they have had a fresh layer accreted to then and the seaward side (shown here) has been eroded. If you know the geography here, these rubble deposits were washed up and over the road which is at the level of the upper deposits in this photo. This photo was taken on the outcrop on the east side of the beach.
[E] WASHOVER OF SAND INTO SOUTHERN PIGEON CREEK
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A wonderful sand washover occurs along the coast
of the southern part of the island. Here in a low area between bedrock
to the west and a well-developed dune complex to the east, sand washed
over and past the dune complex, over the road and into the southern
arm of the Pigeon Creek Lagoon. The location of this washover and the
location of these photos is shown in the map of
eastern French Bay. |
Rushing water resulted in the deposition of a large apron of sand and rubble (E1) This apron washed over the road (where the truck is) and into the bushes associated with the lagoon. A very large quantity of sand was transported in this event. This photo is taken near the beach (the source) looking toward the lagoon. This view is the direction of sediment transport.
The front end of the sand apron. (E2) Ten to 30 cm inclined foresets mark the advancing sand wedge as it prograded into the marshy lagoonal area. A one-cm PVC pipe rests in the front of the sand wedge for scale. View to the east. Flow was south (right) to north (left). Note how the sand apron has prograded into mangroves.
As the surge washed over the hard resistant road, large potholes formed on the other side (E3) These potholes are about 50 cm deep and nearly circular. Presumably they formed due to recirculation of the water after the water washed over the road.
Inland to the protected lagoon (southern Pigeon Creek) and take a sediment core (E4) you can clearly see the sand that has been deposited by Lili ("A"), but not much farther down the core, are three other sandy layers that may represent other washovers. This core was taken in the lagoon (at the edge) some 100 meters from the shore.
If you are an educator who brings students to San Salvador, you should study the locations of these deposits on this map of eastern French (referred to several times above). This map is scanned from part of the San Salvador Island Sheet 2, printed by the Bahamas government, 1972. One square is one kilometer. I added the coastal road from memory. All locations are approximate This is the same map oriented lengthwise for easier printing (but more difficult viewing on the monitor). Shown below is a simple low-resolution version of this map. The Location of this map is shown in the black square in the Satellite image at the beginning of the photo section.
[F] DAMAGE TO HOUSES
CONCLUSIONS
In the long run, Hurricane Lili will be regarded as a major storm that affected the Island of San Salvador. It is clear that wind and waves associated with the Hurricane resulted in local catastrophic sediment transport and ecological damage. Sediment transport, including transport of living coral and sediment washovers, is probably the best geologic record of this hurricane.
Want more information about hurricanes on San Salvador? Try this reference:
Shakelee, R.V., 1996, Weather and Climate, San Salvador Island, Bahamas; Bahamian Field Station ltd., San Salvador Island, Bahamas, 67 p.
The address of this document "SOME EFFECTS OF HURRICANE LILI ON SAN SALVADOR ISLAND, BAHAMAS" is: http://idol.union.edu/~garverj/Geo35/hurricane/Damage.htm
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Last
Revised: 3 January 2003: first posted: 12/15/96