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[Jeff Victor Hayden]

As the reef at Niku seems to play an important part in the Tighar hypothesis I thought it might be interesting to discuss the reef environment and dynamics, especially as we are going to be seeing and hearing a lot more of it in the coming months.
Here's a link to a paper on reef dynamics and sedimentation, copyrighted so you will have to read his work via the link.
http://www.kmec.uhh.hawaii.edu/QUESTInfo/reefsEDM.pdf


Here's a couple of images of a typical reef layout, if you can find any better ones that match the Niku reef that would be helpful.

[Tom Swearengen]

Wonder how much the reef has changes due to seismic activity, and the big waves over the years. That would be interesting to know.

[Jeff Victor Hayden]

This is the Gardner Island seamount (they have it as Niku' on top of the seamount name of Gardner) as it fits in with the surrounding seamounts in the area. It clearly shows the main feature of seamounts, the steepness of the drop-off towards the Abyssal plain.

[Irvine John Donald]

Yikes!!  Thanks Jeff. Those are very dramatic graphics. It just goes to show that this summers expedition needs a vessel and equipment as serious as KoK.

[Gary LaPook]

This is the Gardner Island seamount (they have it as Niku' on top of the seamount name of Gardner) as it fits in with the surrounding seamounts in the area. It clearly shows the main feature of seamounts, the steepness of the drop-off towards the Abyssal plain.

But notice that the vertical scale of the first graphic is greatly exaggerated. Look at the second graphic. Starting at the intersection of 4° 40' S, 174° 30' W (approximately the presumed location of the landing) and going straight west you have to travel 3.06 NM to descend 1,000 meters, the first heavy line. (Each square is ten nautical miles, 18,520 meters.) (For some reason the contour lines above 1,000 meters are not spaced at 100 meters as the legend states. Or, if they are, then the color coding is wrong.) 3.05 NM is 5,660 meters. 1,000 meters of descent over a horizontal distance of 5,660 makes the slope only 10.2°, not nearly as steep as it appears at first blush. (If the contour lines are actually 100 meters then the first heavy line is only 500 meters so the angle would only be 5 degrees instead of 10.) Does anybody know the angle of repose of pieces of aluminum on a bed of coral? I suspect that it is a lot steeper than ten degrees.

gl

[Jeff Victor Hayden]

Yes Gary, I think the first image is for illustrative purposes only, not to be taken as gospel. Here's a link to the seamount catalog that might help...
http://earthref.org/cgi-bin/sc-s2-list.cgi?database_name=sc&search_start=main&selected_smnt_id=65

[Jeff Victor Hayden]

Spur and groove video from Youtube. Must be shallow water due to the presence of the scuba divers but, gives us some idea as to the landscape. Any video or images of spur and grooves or even a reef at 300 meters would be captured using an ROV, haven't found any, yet.

http://youtu.be/Na4dMzVp-aY

[Andrew M McKenna]

That video is fairly representative of the reef at Niku just offshore of the break in the reef flat, shallow water down to about 30 ft.  Below that the grooves are basically lost in the sauce, so to speak.  None of the 2010 ROV video was taken in this area as I understand it, they started farther off shore in deeper water, but in 2001 we did dive most if not all of the spur and grooves between the landing channel all the way up to near the NW tip of the island.  We literally swam up each groove from slightly offshore where the grooves were some 20 ft deep right on up to the surf line where the reef flat starts.  Made for some interesting diving with the surge that was also trying to move up and back through the grooves.

Andrew

[Jeff Victor Hayden]

Very good points, well presented.
I would add that as the surfaces of the wings and tailplane etc... were designed to provide lift and control during flight through air then, they would still perform this function when water, moving fast enough, passed over them. A bit like a sail on a yacht catching the wind maybe. Currents, tides, storms...?
Just a thought.

[Jeff Victor Hayden]

Gary
This link has quite a lot of research data from the Phoenix islands including Nikumaroro. The slope on the reef is given as being between 45 and 85 degrees depending on how far you are from the surf line and the location.

http://www.phoenixislands.org/pdf/00589.02.pdf

[Gary LaPook]

Gary
This link has quite a lot of research data from the Phoenix islands including Nikumaroro. The slope on the reef is given as being between 45 and 85 degrees depending on how far you are from the surf line and the location.

http://www.phoenixislands.org/pdf/00589.02.pdf

That report is interesting but its purpose was to catalog the reef area for ecological research purposes. It does make the general statement that the slopes vary from 45° to 85° but that is not specific to Gardner. In fact it points out that offshore of Gardner "on the western shore where the reef drops from the intertidal rim to > 40 m within 50 m in some locations." The clear reading of this is that most of the reef is not that steep but only in some locations is it that steep. Taking "> 40 meters " as meaning approximately 50 meters, within 50 meters makes the slope, in some locations only, approximately 45°. This is apparently so unusual that it required this specific comment.

Looking at the bathymetric map again and this time looking to the east along the 4° 40' S parallel and looking at the spacing between 1,000 and 2,000 meters of depth covers 1.9 NM, 3,600 meters making the deep slope in that area only 17° so the 45° to 85°  slope statement does not appear to be applicable to the reef around Gardner.

So unless there is some reason to distrust the bathymetric chart I think it trumps the general statements in the report you referenced.



gl

[Jeff Victor Hayden]

Yes, there hasn't been a lot of oceanography research in this part of the Pacific Gary.
  'Because of their large numbers, many seamounts remain to be properly studied, and even mapped. Bathymetry and satellite altimetry are two technologies working to close the gap.'
As you mentioned, the drop off varies quite considerably around the Gardner Island seamount. Will be interesting to see the actual slope where the aircraft wreckage is theorised to be this coming July.

[Andrew M McKenna]

Here are some items that should help us understand the reef and how fast it drops off.

Courtesy of James Thompson of GIS Services is a series of graphics of the soundings made by the Bushnell Survey of 1939.  Jim took the soundings made by the Bushnell and input them into his GIS software to create these interesting items such as the .kmz files that can be opened in Google Earth.  You can select a single sounding in GE and it will tell you the coordinates and the depth.

For the file called TIN2.pdf (the colorful one), make sure you zoom way in and you will see the locations and actual Bushnell soundings recorded.  The color stuff is actually overlaid on top of the actual Bushnell survey which you can see around the far edges.  I think it is a beautiful piece of work by Jim Thompson.

Gary, having been diving on the reef, most of it gets pretty steep, pretty quickly, not just in "some places" - the nearest soundings to shore start at 30+ fathoms and drop off quickly to 300+ fathoms, so I don't think 17 degrees is accurate.  No doubt you will calculate the angle from the info in the Bushnell survey, and I look forward to your analysis.

Andrew

[Jeff Victor Hayden]

Andrew, thanks for the information. Your task ahead does seem to be more daunting than I realised. I wish you all the best of luck.

[Andrew M McKenna]

Thanks for the vote of confidence, but I'm not going on the upcoming trip.  Wish I were, but it will mostly be a pretty small crew of specialized folks.

By the way, it is not my task, or even Ric's task, it is OUR task.  Like it or not, you are all involved now, sucked into the vortex, part of the process and the project.   

Andrew