2011-03-09 03:59:15The dynamic responce of reef islands to sea-level.Webb+Kench
Klaus Flemløse

KlausFlemloese@mail.tele...
62.243.102.250

I have read the following paper by Webb /Kench:   

"The dynamic response of reef islands to sea-level rise: Evidence from multi-decadal analysis of island change in the Central Paci
fic"
http://www.pacificdisaster.net/pdnadmin/data/original/The_dynamic_response.pdf
 
To me this paper seemes OK and it will change the discussion on sealevel increase around reef islands like Tuvalu.
I think  "my good old friend" prof. Axel Mörner will be very happy about this paper in addition to Whatsupwiththat.
 
The geomorphology of reef islands is a complicated matter, I would be pleased if some could start writing about paper.
It is too difficult for me since it is far away from my knowledge. 
 
2011-03-09 05:53:17
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.205.107

Klaus - see the advanced version of "coral atolls grow as sea level rises" here. The whole idea that corral rubble and sand could be stable for millenia never ever made sense to me. Have read the Webb/Kench paper. Newspaper reports on the situation were somewhat exaggerated, but for atoll islanders by mid/late century the gig will be up.

2011-03-09 06:40:31Thanks for Link
Klaus Flemløse

KlausFlemloese@mail.tele...
62.243.102.250

As a layman I have the following questions:

60% of Tuvalu atols have a oceanside erosion and atolside build up.

Is asymmetry normal ?

If an erosion  has started,  will there at first be an area increase of the beaches because of new material is added. Later on  - when the new material has been remove by sea waves - there will be a significant decrease of area of the whole atol ?

Will it be correct to state, that the 60% erosion is a sign of danger ? 

2011-03-09 16:19:47
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.197.178

Klaus, the prevailing wind is the side of the atoll which has the most growth because it is bathed in nutrient rich water bought by the winds (the tropical and sub-tropical ocean being more or less a marine desert). In the Pacific this is the eastern side due to the trade winds. Typically this is also the side which accumulates the most sediment (but not always). So yes, that kind of asymmetry appears to be normal.

I don't know that erosion of the atoll has started, the Webb/Kench paper indicates that thus far, there seems to be a small net gain in land area. Debris swept away off the atolls is replaced by new coral rubble and sand, as waves erode and breakdown growing coral (and other hard-shelled marine organisms). Sand cays, which don't have a solid base above sea level, tend to change a lot over the course of decades, and large storms can sometimes wipe them out completely even if they are well vegetated.

Webb/Kench only looked at Tuvalu, a handful of atolls amongst many. So what the Pacific wide trend is?, I have no idea. But given the small increases in sea level thus far it would not surprise me if there wasn't much change. Of more immediate concern are the potential for greater storm surges, and and the possibility of changes in precipitation (atolls having a freshwater lens that is wholly dependant on rain falling on the atolls).   

Very long-term a decline in coral growth would lead to a fall in atoll area, as sediment export exceeded import. But given the studies on reef and cay erosion that I've read, that would be a fair way off.