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Author Topic: The Slope of the Reef around Nikumaroro  (Read 39508 times)

Ric Gillespie

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The Slope of the Reef around Nikumaroro
« on: February 12, 2013, 08:13:19 PM »

But this whole plane superstucture hanging around just underwater, in perhaps 10-20 feet of water, visible at certain times and tides is far fetched to me and doesn't fit with the near vertical drop off once past the breakers that has been described by visitors.

I don't know what visitors you've been listening to but there is definitely an area of shallow water sloping down to depths of 60 feet or so before the first cliff drops off. 
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william patterson

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Re: The Slope of the Reef around Nikumaroro
« Reply #1 on: February 13, 2013, 07:44:58 AM »

But this whole plane superstucture hanging around just underwater, in perhaps 10-20 feet of water, visible at certain times and tides is far fetched to me and doesn't fit with the near vertical drop off once past the breakers that has been described by visitors.

I don't know what visitors you've been listening to but there is definitely an area of shallow water sloping down to depths of 60 feet or so before the first cliff drops off.

I have been listening to you.
 I have never visited, so I like 99% of others rely on Tighar for the description of everything to do with the island. Unfortunately in visualizing and also in descriptions the areas sometimes change drastically depending on which small section is being mapped and how the charts are drawn. The Wiki description honestly is confusing as it goes back and forth describing windward and leeward sides, when windward and leeward can change. Is Windward around the Norwich or is that considered leeward? At one point the Wiki reference seems to include the Norwich side as the leeward side. When in other references it states from March to November is the "westerlies", so the Norwich side would be the windward side. It might be easier to describe it by landmarks or compass points.

The  general description I have gathered is the south(leeward side) has a shelf (or shelves) and a spur and groove section on the site seven section, variously called the Northeast, but also the southeast side. The one common description from Tighar is that the area around the Norwich was drastically steeper and contained few ledges to hold a wrecked craft. Yes there is water from one foot to 1000 feet, but is the area around the Bevington photo shallow enough AND with a low enough slope to hold wreckage and also to play peek a boo depending on the time of day and weather?

From the Wiki reference-
"Beyond the reef edge is the steep drop-off zone. The average gradient of the upper submarine slope down into the abyss is about 40º"


This indicates a very steep slope which would have a hard time holding a relatively light aircraft. If the wreckage is assumed to be in 20 feet of water(is that the current theory?), then what is the slope there? If it's in 50 feet of water what is the slope there? Are there wide enough ledges with low enough slope to withstand tidal action and storms in that particular section of reef. The Wiki reference material doesn't seem to indicate that at all.

Like a lot of folks just trying to grasp the simple verbal description of what side a lambrecht photo was taken, there seems to be much confusion(by myself first in line), as to what this dynamic reef looks like underwater, and I suspect a lot has to do with where on the atoll the measurement is taken. You go 50 meters around the circumference and it seems to change.

The one thing that does seem clear is there is a much steeper slope, sometimes referred to "almost vertical" by yourself, on the Norwich side along with reef undercutting. We have descriptions of ships not being able to anchor around the Norwich because of the depth and slope and having to tie off to the Norwich.
Why couldn't they anchor if there is a 60 foot deep wide stable flat that can hold an airplane? In my opinion, No Anchorage means there are no flats like you now describe in the Bevington area.

This doesn't sound like a wide, low slope 30-60 deep flat in that particular 200 meter wide area around the Norwich. At least not with a slope in 20ft-50ft range where a plane could hide out and re-appear. Obviously if it's too shallow a relatively larger aircraft will be visible, and if too deep it will never appear to the islanders. Like the 3 little bears, this peek a boo theory has to be just right, with just the right slope and just the right depth, and relatively protected from violent storms.
I just don't see a plane hanging up in a 3 little bear area, not near the Norwich. It seems too dynamic, steep, and violent.

I will say while the color sonar maps are great, if they were marked in depth and slope it would give a much better understanding to non visitors and casual readers trying to grasp the full scope of the island.
 I wish there were better marked maps and graphs, Graphs like the following are hard to interpret and very simplistic, which makes much ambiguity whether talking about tidal datums or areas plane wreckage could be hidden.
http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/TidalStudy/reefflat.html

So from the graphs and descriptions provided, a  high slope, steep dropoff, no anchorage, it would seem the wreckage would have to be in the perfect spot, on the perfect little ledge, just sitting there for years for Emily to spot it, and that to me seems unlikely.
I think it went deep and went deep fast if the wash off the reef theory happened anywhere on the Norwich side of the Island.
« Last Edit: February 13, 2013, 08:13:12 AM by william patterson »
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Greg Daspit

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Re: The Slope of the Reef around Nikumaroro
« Reply #2 on: February 13, 2013, 09:18:38 AM »

 Attached is a pdf of my understanding of the reef and underwater debris field from descriptions, and photos. I have added my own speculations just to test and study. I modify it as I learn more so it is just my interpretation to date and may be wrong or incomplete. Also attached is a reef survey Ric previously posted. My pdf, like many graphics is only a general diagram/ sketch. It's not a surveyor's profile drawing with the benifet of alot of elevations shot.
I inserted a picture of a strut to show it gets rust colored and the kite photo to show what looks like crevices and holes nearby the estimated Bevinton Object location.
(edit pdf to show 197' dim. instead of 97')
3971R
 
« Last Edit: February 13, 2013, 10:04:33 AM by G. Daspit »
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Ric Gillespie

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Re: The Slope of the Reef around Nikumaroro
« Reply #3 on: February 13, 2013, 09:18:54 AM »

Let me see if I can clear up some confusion.  The long axis of the atoll runs roughly NW to SE. The long shoreline that runs from the NW tip, past the Seven Site, to the SE tip where the Loran station was is referred to as the "windward side" because the prevailing wind in from the East.  All other shorelines are on the "leeward side" of the island.  Severe weather almost always comes out of the west and northwest ("westerlies").  On those occasions the west side of the island where the shipwreck is takes the brunt of the wind and waves.

Along that western shoreline from Norwich City northward to the Bevington Object location our knowledge of the reef profile is derived from
1. observations on the surface at low tide
2. photos and video taken by scuba divers at depths from the surface down to about 100 feet.
3. ROV video, multi-beam and side-scan sonar images at depths greater than about 200 feet. 

We know from scuba divers and ROV video that just offshore the spur & groove zone the reef drops off to a level or mildly-sloping shelf that varies in depth from roughly 20 to 40 feet, then the slope steepens down to a depth of about 80 to 100 feet at which point it drops almost vertically about 200 feet.  The attached photo was taken at a depth of abut 60 feet.  This region from the reef edge out to the first cliff was too shallow to be mapped by KOK's ship-mounted multi-beam sonar and too hazardous to be mapped by the AUV's side-scan sonar.

The attached map of ROV Dive 13 shows the "snail trail" of the ROV as we searched the mildly sloping shelf at the base of the first cliff.
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C.W. Herndon

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Re: The Slope of the Reef around Nikumaroro
« Reply #4 on: February 13, 2013, 09:52:09 AM »

The attached map of ROV Dive 13 shows the "snail trail" of the ROV as we searched the mildly sloping shelf at the base of the first cliff.

Ric, I don't see an "attached map of ROV Dive 13". Am I missing something?
Woody (former 3316R)
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Ric Gillespie

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Re: The Slope of the Reef around Nikumaroro
« Reply #5 on: February 13, 2013, 09:58:52 AM »

Ric, I don't see an "attached map of ROV Dive 13". Am I missing something?

Oooops!  Sorry.

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C.W. Herndon

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Re: The Slope of the Reef around Nikumaroro
« Reply #6 on: February 13, 2013, 11:25:31 AM »

Ric, I don't see an "attached map of ROV Dive 13". Am I missing something?

Oooops!  Sorry.

That looks great. Thanks.
Woody (former 3316R)
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william patterson

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Re: The Slope of the Reef around Nikumaroro
« Reply #7 on: February 13, 2013, 12:57:39 PM »

Thank you Ric, that is most helpful. If I may, a followup just to make sure I am on the same page.
So on the snail trail graph, the area marked in Black that says "first cliff not mapped", that black area on the snail trail map is 20-40 deep and it does not include the spur zone? It is seperated from the spur zone?

If I am understanding correctly the spur zone does go dry periodically(or not?) and that spur zone is the area where in theory the bevington object was at? That would be in 3 feet of water at high tide?

Then offshore of the spur zone is the blackened area not scanned that has a mild slope and is 20-40 feet deep?
So what is being called the "first cliff" is the dropoff from the spur zone into the mildly sloping 20-40 waters where it is theorized
a wreck may have hung around for some time. Eventually dropping down successive cliffs.
Is that the correct picture?
How wide(from spurs to second cliff) is this blackened area not mapped that is relatively shallow? Did suba divers cover the whole area?
(it would really help if you could just fly everyone out to look for themselves! Haha)
Also thank you Mr.Daspit for your PDF as well.
« Last Edit: February 13, 2013, 01:06:25 PM by william patterson »
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william patterson

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Re: The Slope of the Reef around Nikumaroro
« Reply #8 on: February 13, 2013, 01:24:40 PM »

Jeff, I think Ric was describing the spur zone as different from the "not mapped" blackened area on his graph.
I think it goes like this from Rics latest description-

Reef flat 200 meters wide from beach to end of spur zone
Then spur zone(not sure how wide this entails)
1st cliff off the real shallow spur zone into 20-40 feet of moderate slope coral.(again not sure how wide this non mapped area is)
Then another dropdown to 100 feet of water where slope increases to "moderate" (that area looks very narrow on the photograph provided)
Then 2nd cliff to 200 feet which is almost vertical.

At Least that is my limited understanding. I don't think divers were covering the Spur zone, but were diving out past the spur zone.
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richie conroy

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Re: The Slope of the Reef around Nikumaroro
« Reply #9 on: February 13, 2013, 01:56:55 PM »

Hi All

Ric Can you confirm if this video was recorded at Niku 2010 expedition ?

 http://www.youtube.com/watch?v=iCs1r2TmRz4

Thank's Richie
We are an echo of the past


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Tim Mellon

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Re: The Slope of the Reef around Nikumaroro
« Reply #10 on: February 13, 2013, 02:38:46 PM »

Balderston Debris Field (red oval):

Tim
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« Last Edit: February 14, 2013, 11:09:17 PM by Tim Mellon »
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Greg Daspit

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Re: The Slope of the Reef around Nikumaroro
« Reply #11 on: February 13, 2013, 04:35:01 PM »

Some of  those areas do look dangerous for divers but difficult for ROV’s and dangerous for the ship.
Seems like divers are needed to get at hidden coral covered artifacts where an ROV could collide and cause avalanches, but any avalanche would be unsafe for the diver. The 2012 Debris Field seems accessible for divers but how do you safely search those areas?

If the underwater reef debris might be farther north how would it impact a Camp Zero search?
Seems like the bottom of that notch in the beach line is close to wherever the plane may have stopped in that zone and is a good place to look.
PDFs attached
3971R
 
« Last Edit: February 13, 2013, 05:35:57 PM by G. Daspit »
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Tim Mellon

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Re: The Slope of the Reef around Nikumaroro
« Reply #12 on: February 13, 2013, 06:01:36 PM »

Ric, you sound even more certain than I!
Tim
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william patterson

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Re: The Slope of the Reef around Nikumaroro
« Reply #13 on: February 14, 2013, 02:33:53 AM »

Jeff, I think Ric was describing the spur zone as different from the "not mapped" blackened area on his graph.
I think it goes like this from Rics latest description-

Reef flat 200 meters wide from beach to end of spur zone
Then spur zone(not sure how wide this entails)
1st cliff off the real shallow spur zone into 20-40 feet of moderate slope coral.(again not sure how wide this non mapped area is)
Then another dropdown to 100 feet of water where slope increases to "moderate" (that area looks very narrow on the photograph provided)
Then 2nd cliff to 200 feet which is almost vertical.

At Least that is my limited understanding. I don't think divers were covering the Spur zone, but were diving out past the spur zone.

Thanks, William.

I guess I'm still not so clear on it - it just looks from the photos showing the deep crags in the surf and the black unmapped zone that there might be fertile turf for hiding stuff there.

Well me and you both Jeff. Cause it's confusing.
 The graph from Ric which shows "unmapped" and "1st cliff" in black,  doesn't show how wide that is. It also doesn't show depth of the blackened in area.  In the graph there is also no spur and groove zone shown at all, it's all marked black. So is the spur and groove zone part of this unmapped area? How deep is it on the spur and groove zone and how much does it vary in water height during tides? Is there a drop off from the spur and groove zone into 20 feet of water or a slow transition?

In The video from Ritchie posted above, which is unmarked, he asks is this Niku 2010? Good question, because if it is it shows an ROV running right through this 20 foot depth marked with boulders and craggy peaks, and it looks like a small area, quickly dropping to 40 feet, then 100, then 400, ect. The shark in the video looks to be in about 40 feet of water, so that is too deep for a peek a boo plane. The boat seems no more than 400 meters from the beach, which is very interesting. (and brave)

Is the 20 foot deep boulder strewn nightmare of crevasses and holes part of the spur and groove zone seen clearly as WHITE/TAN in overhead photos? I do not think so.  From Ric's description and graph, the spur and groove zone is NOT the 20 foot deep area. If I am correct and understanding Ric, the 20 foot deep area suspected of holding the wreckage is just past the Tan colored spur and groove zone. The 20 foot depth is a fairly small LIGHT BLUE area before quickly dropping to DARK BLUE looking water as shown on overhead photos. The transition area from light blue water to dark blue water seems very small.

This transition area of 20 foot depth seems very small to catch a plane, it is not a broad flat expanse, and quickly drops to dark blue water 40-60 foot.  60 foot deep is too deep for the plane to be seen periodically.(unless it held air and was bobbing which I have doubts about)
So it is important to know just how much total area comprises this approximate 20 foot deep water which would seem the ideal depth for holding a peek a boo plane. Deeper than 20 feet and it gets problematic that Emily ever saw anything. More shallow than 20 feet and its basically on the reef flat or on the spur and groove section, and would be seen at every tide change and I don't see how Maude missed it.

An overhead kite photo(s) of the Bevington area, marked off with all snail trails, marked off with depths and cliffs, marked with width and area, showing water color transitions as it goes from shallower water, to darker blue water that is too deep to hold a plane that sometimes appears partially visible,  would be a wonderful thing to sort out the brain. We have the kite photo showing water heights on the reef, but not a kite photo marked up past the reef edge showing descending depths of the blue water.

Trying to make sense of things unseen with one's own eyes and based on descriptions, photos, maps and graphs and combine them all in the frontal cortex is a difficult thing.
I am sorry Ric if it's like talking to a kindergarden class, but there is still confusion.
« Last Edit: February 14, 2013, 03:33:08 AM by william patterson »
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C.W. Herndon

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Re: The Slope of the Reef around Nikumaroro
« Reply #14 on: February 14, 2013, 07:26:28 AM »

Very interesting comments Jeff. I have been looking at some of the reef photos that have been posted and found this one. The red "X" is the estimated location of "Nessie" at some time, I'm not exactly sure when. If you look at the area that I have enclosed with the "red rectangle" it looks like a hole in the reef. I don't know if it can be determined from old photos how long the "hole" has been there but if it has since 1937, it would seem, to me at least, this might be a place that could hold pieces of an Electra, maybe?
Woody (former 3316R)
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