The Island of the Palisadoes? Edward Robinson and Deborah-Ann Rowe Marine Geology Unit Department of Geography and Geology University of the West Indies Mona, Kingston 7, Jamaica mgu@uwimona.edu.jm
Was the Palisadoes ever an island? Will it become one in the future? 2
Palisadoes New Beach 4
So, for a short time, the Palisadoes was an island. 5
What is, or are the Palisadoes? 6
Palisadoes, a Spit Complex Green, land areas; yellow, shoals inside the harbour, cays outside the harbour; blue line, edge of deeper water inside the harbour; peach line, extent of shallow water; orange line, southern side of Palisadoes spit complex. 7
To hazard a guess at what will happen to the Palisadoes tomorrow, one needs to know how it got to the stage it is at today. 1
What moves the beach sediment?
Waves
Break ing W aves
Sediment Transport 12
Dunes 13
SEDIMENT TRANSPORT DIRECTIONS 14
When water waves reach shallow water, they feel the seafloor. This results in the waves slowing down, the shallower the water, the slower they move until eventually they break. Because the seafloor is at different depths in different places, each wave is slowed down at different rates in different places, so that they tend to bend in the direction of the shallowest water. This is called WAVE REFRACTION. 15
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What is the source of the sediment? The mouth of the Hope River post Hurricane Ivan 17
Palisadoes sediment sources 18
Rare Destructive Events 19
Earthquake Fissuring of the ground after the 1907 earthquake, due to liquefaction. liquefaction. This T his site is close to the eastern end of the Palisadoes (photo, West Indies Reference Libr ary). 20
Earthquakes From the point of view of damage to Port Royal and the Palisadoes, the worst earthquake in historical times was that of 1692, which destroyed much of Port Royal, with largely unknown effects on the rest of the Palisadoes 21
Hurricane PART OF GASCOIGNE S MAP OF 1728 22
Holes in the Palisadoes Approximate positions of breaks in the Palisadoes (A to E) resul ting from the 1722 hurricane. Depths inside the harbour from the 1960 Kingston Harbour Harbour study; depths outside the Palisadoes compiled from British Admiralty surveys. 23
Post-Ivan Palisadoes J. Tyndale-Biscoe Co. 24 Ltd
Palisadoes Groyne 25
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Airport Region 18th Century Grey Solid Ground Green Mangrove Swamp Red Dune Ridge 27
Airport Region 1938 Grey Solid Ground Green Mangrove Swamp Red Dune Ridge 28
Palisadoes Steers Photo 29
Structural Mitigation Groyne field Boulders 30
Geological Mitigation Beachrock 31
How did the Palisadoes Form? 32
STEP 1 Initial Development of the Spit Black line, spit; green, cays; yellow, shoals; peach line, extent of shallow water. 33
STEP 2 Evolution of a new spit (2) extending from what is now Plumb Point Point and capturing the sediment supply from the previous spit (dashed line). Black line, spit; green, cays; yellow, shoals; peach line, extent of shallow water. 34
STEP 3 A new spit (3) developed from what is now Little Plumb Point, em embracing bracing the shallows associated with the hurricane refuge. Black line, spit; green, cays; yellow, shoals; peach line, extent of shallow water. 35
STEP 4 Longshore drift extended a spit (4) from Little Plumb Point put past what is now Gallows Point to the edge of the deep channel. Black line, spit; green, cays; yellow, shoals; peach line, extent of shallow water. 36
STEP 5 T he final stage in the development (5) of the Palisadoes through extension of the spit complex to Port Royal Black line, spit; green, cays; yellow, shoals; peach line, exten t of shallow water. 37
What of the future? 38
Lowest part of road 39
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WESTERN PALISADOES NET CHANGES 1949 TO 2002 41
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Thank You 44
The Marine Geology Unit Department of Geography and Geology University of the West Indies Mona Campus Kingston 7 JAMAICA Tel: (876) 927-2728, (876) 977-1441 Fax: (876) 977-6029 Email: mgu@uwimona.edu.jm Website: http://www.mona.uwi.edu/geoggeol/mgu/ 45
The information in this presentation is to be used only with the permission of the Marine Geology Unit. Please acknowledge the sources of all information and data. Give credit to the authors and respect their copyrights. The Marine Geology Unit is in no way responsible for the use of the information contained herein. 46