POSSIBLE IMPACT CRATERS
Geological Structures That May Be Meteorite Craters
by: Charles O'Dale
During my aerial meteorite crater explorations over various points of the North American Continent, I have noticed and documented a few geological features that are suspiciously shaped like meteorite craters. Also, I have investigated a few that were suggested by people who have contacted me after reading my meteorite articles. I have listed below the “crater like” structures that I have documented and will be periodically adding more features as I visit them. If you have any information on any of the ones I have documented or any new possible meteorite craters, please to let me know.
A strongly negative magnetic anomaly (graphics at right) coincides with the lake. D. H. Hall (University of Manitoba) calculated that the removal of a block of the slightly magnetic country rock granite would produce the negative anomaly over the lake.
La Moinerie Crater area Unknown Lake
Note the esker visible on the right (west) part of the circular lake. This “might” indicate a shallow part of the lake caused by a rim structure.
North Quebec Possible Crater Chain – six features
I documented the circled crater on the bottom of the superimposed oval after exploring the Pingualuit crater. I was headed south west from Kuujjuaq toward the Clearwater Lakes meteorite craters, and diverted to explore this feature. I had noticed on the aeronautical chart that it was a circular “crater like” structure worth exploring. At the time I was unaware of the other similar shaped lakes in the area. Except for the noted documentation on Kakiattukallak Lake, I have not found any documentation relating to any impact investigations for these sites.
The following is a quote from the February 1975 issue of the Journal of the Royal Astronomical Society of Canada:
“Kakiattukallak Lake, Quebec (N 57° 42’ W 71° 40’) – a roughly circular lake averaging 6 km in diameter in low relief Precambrian terrain. During a recent reconnaissance visit several breccia boulders were recovered from the shoreline. The breccias are considered to be shock produced but exhibit a level of deformation slightly below that at which distinctive shock features are formed. (P.B. Robertson and R.A.F. Grieve)”
The superimposed circle on the aeronautical chart indicates the position of Charity Shoal. Note the magnetic anomaly indicated to the east of the shoal “magnetic disturbance of as much as 9° exists at lake level in this area”. Could this magnetic anomaly be the result of an impact by an iron meteorite? Verification as an impact crater will require detailed geophysical surveys and collection and analyses of samples from in and around the structure. My aerial exploration of the crater was rather disappointing. Nothing of the bottom of the lake was visible when I was directly over the feature (confirmed with GPS). The peak of the shoal directly to the north, shown in this image, was the only part of the shoal I could see from about 2000 feet over the water (so I could remain within gliding distance of land on engine failure). An underwater exploration trip is in order!National Oceanic & Atmospheric Administration (NOAA), U.S. Department of Commerce. A side-scan sonar survey has identified a 19+m deep, 1000m diameter circular feature in Lake Ontario. It is completely surrounded by a low relief rim that rises to within 5m of the water surface. It consists of bedrock of middle Ordovician limestones 100-150 m thick overlying rocks of Precambrian age. Relief of the feature is low compared to that typical of an impact crater of this size. Glaciation may have diminished relief by eroding the rim and filling the central basin with drift.
A sediment sample collected from the crater floor was stiff, varved lake clays covered with a thin layer of coarse sand. The time of the structure's formation cannot be determined, but likely times include the Pleistocene when the area was exposed by glacial erosion, the middle Ordovician near the time of deposition of limestones, or the Cambro-Ordovician or Precambrian when erosion surfaces of this age were exposed. The structure is imbedded in the limestone formation typical of that around the Kingston area and may be a sinkhole, volcanic cone or kettle. (Edsall, T.A., Brown, C.L., Kennedy, G.W., and French, J.R.P. III. 19912. Surficial substrates and bathymetry of five lake trout spawning reefs in nearshore waters of the Great Lakes. Great Lakes Fishery Commission Technical Report 58, Ann Artbor, Michigan.)
Private Correspondence from Mr. John Warren, Canadian Hydrographic Service (CHS) - Charity Shoal is a 19+m deep, 1000m diameter circular feature in northeastern Lake Ontario. Bathymetric analysis (T.L. Holcombe, J.S. Warren, D.F. Reid, W.T. Virden, and D.L. Divins, 2001, Note: Small Rimmed Depression in Lake Ontario: An Impact Crater?, J. Great Lakes Res., 27(4): 510-517) suggested that it may be an impact crater (see images left and right). As a result, the Geological Survey of Canada collected samples of the rocks from the site in the hopes of discovering the origin of this feature, but the results were inconclusive and more detailed sampling, including drilling, would be required.
An earlier side-scan sonar survey (Edsall, T.A., Brown, C.L., Kennedy, G.W., and French, J.R.P. III. 1991, Surficial substrates and bathymetry of five lake trout spawning reefs in nearshore waters of the Great Lakes. Great Lakes Fishery Commission Technical Report 58, Ann Arbor, Michigan.) provided some information about the surrounding terrain and substrate, but failed to identify it as a possible impact structure. It is completely surrounded by a low relief rim that rises to within 5m of the water surface. It consists of bedrock of middle Ordovician limestones 100-150 m thick overlying rocks of Precambrian age. Relief of the feature is low compared to that typical of an impact crater of this size. Glaciation may have diminished relief by eroding the rim and filling the central basin with drift.
Alsever Lake & Round Lake
- Diameter: ~4 Km
- Location: Algonquin Park, Ontario, Canada N 45° 41’ W 77° 59’ (~115km SE of Brent Cater: N 46° 05' W 78° 29')
Brent Crater and the Alsever/Round Lake combination on this landsat image to illustrate the relative position of this “crater like” structure. The Ottawa River is shown meandering to the north of the feature.
The Alsever and Round Lake combination is illustrated here on an aeronautical chart, and details their striking similarity to the Gilmour and Tecumseh Lake combination within the Brent meteorite crater.
These images of Alsever and Round Lakes, taken from the west (top) and east (bottom), again show their similarity to the Brent Crater. A closer look at the image of the structure taken from the west shows the granite cliff of the center feature interfacing Alsever Lake.
This implies that the center feature that divides the two lakes is granite, unlike the sedimentary debris in the center of the Brent Crater. In the future I plan to do a surface exploration of this area. Who knows, I might get lucky and find a shatter cone!
REPORT ON ALSEVER EXPEDITION(S) – AUGUST-OCTOBER, 2010
Prepared by Eric Kujala February 10, 2011
On August 6, 2010 Chuck O'Dale (to the right in the image) and I embarked on an aerial exploration of Algonquin Park. Our flightplan took us from Rockliffe Airport, Ottawa to Brent Crater at the north end of the park and then south to a lake called Alsever.
Alsever Lake (image left) is located at the southern boundary of Algonquin Park. It is similar in appearance to the Brent impact structure (image right) with its two distinct bodies of water forming a circular pattern. Alsever has a central "land mass" like Brent and what appears to be circular outline. This is best viewed on some topographical maps.
We surveyed and photographed as much of the area from the air as we could to prepare for a subsequent ground expedition. It was difficult to assess from the air which way was best to reach the lake but it gave us a good perspective on how big the site was and the general landscape. These are details you do not get from maps.
In September, 2010 we undertook a ground day-trip by car to orient ourselves. We learned from the Algonquin Park authorities that the north end of the site was not accessible due to park rules. There is a utility road used to service hydro transmission lines just north of the site. Only park staff and the native community have access here.
We found an alternate entrance from Aylen Lake to the south and hiked up a “cart trail” that leads to the Alsever lake area. Unfortunately we took a wrong turn and ended up east of our intended destination. No single map offers a complete and accurate description of the area. The park map indicated a portage route but no cart trail. Other maps did not indicate portage routes. We combined the information from all our maps to come up with a route that would offer our best chance of reaching Alsever.
On Friday, October 22, 2010 we returned to Algonquin Park for a 3 day excursion to Alsever. Along with the necessary camping equipment we brought our trustee 17ft. Old Town Tripper canoe.
After getting our parking and camping permits from Aylen Lake Marina we drove to the end of the park road leading to the cart trail. The trail is an old logging road which has been abandoned. A ditch was dug to prevent cars from going further down that trail.
We parked the van at the end of the road where the cart trail begins at the southern boundary of the park. The canoe was fitted with cart wheels. This would allow us to carry our equipment down the 4 KM stretch of trail which would lead to the Aylen River. Chuck used a set of trekking poles and a harness to pull the canoe. I carried some of my gear on me and steered from the back to keep it on the trail.
The Aylen River (image left) intersects the cart trail at one point where there is a foot bridge and then runs northwest parallel to it for 2 KM. The stretch that runs parallel is not navigable as we would later find out. Our trail hike led us down to a short portage that links the trail to the river. We had to carry our gear and the canoe from here since the portage was too rough for the cart wheels under the canoe. The portage is about 60 meters long. Once at the river we loaded up and headed north. The river on average is about 20 meters wide. It is shallow and has numerous beaver dams and lodges.
There is a large beaver dam about 50 meters up from the point where we take into the river. We had to get out of the canoe and haul it over the dam and then keep going north against the flow of the current. The current was not strong and so paddling was not a problem. We encountered seven more dams on the way up. We paddled approximately 10 KM until we arrived at the point where there was a portage trail leading to Alsever.
We saw a moose grazing shortly before arriving at that point. Because it was late in the day we decided to make camp. We made a short visit up our first portage trail Friday evening to inspect the condition of the trail. We found it adequate for us to plan our trip the next day. Chuck was visited by the moose that evening. We think it’s the same one. He (or she) made his presence known and knocked over a couple of trees near Chuck’s tent. Moose are territorial. He may have been drawn by our presence. The area is rarely visited in October.
It was cool and clouded over Friday night and then snowed. I was not able to make any significant astronomical observations. Saturday morning October 23, I found Chuck having breakfast in the snow. We prepared day packs and our canoe for the two upcoming portages. We would leave our base camp as is for the day. Now it was time to haul!
We portaged from the campsite on the shore of the Aylen River north to Pond Lake a distance of about 650 meters. We took a small break and then proceeded across Pond Lake a distance of about 200 meters to the next portage. The portage signs were all clearly visible on our trip. From Pond Lake we portaged about 750 meters to Aylen Lake. We paused at the short of Aylen and then put the canoe in. This was what we had been waiting for since our aerial exploration in August. It is frustrating to be so close to a site of interest from the air and not be able to inspect it like a ground expedition offers.
Once on Alsever Lake our goal was to find solid evidence this was an impact site. Impact melt, shattercones and altered structures of quartz known as planar deformation features are good evidence for an impact site.
We proceeded in a counter-clockwise direction around Aylen Lake. We stayed close to shore in order to be able to detect anything of interest. We kept a sharp eye for evidence such as shattercones or impact melt. In the shallow water we could see moose tracks left in the mud. We saw many beaver lodges. One of my concerns on this trip was the drinking water. Beavers have a parasite that thrives in lake water and can cause illness sometimes known as “beaver fever”. Filtering and preferably boiling the water before drinking it is important.
About an hour into our lake exploration we arrived at our target site, an outcropping we had spotted in our aerial exploration (image left). This exposed rock might give us the evidence we were looking for.
The rock is mostly igneous. We found pegmatite in the rock. The outcropping was geologically interesting but did not offer any evidence of an impact site.
Although some rocks on the shoreline had what looked like striations in them, they were not shattercones. On many previous explorations we had seen ample signs of impact melt and shattercones. At Manicouagan we saw a hill of impact melt. Chuck also found some shattercones there. On our 2008 exploration of Pingualuit (Chubb) we found impact melt. Even though the Pingualuit crater “looks” like a crater, its mere appearance does not provide scientific evidence that it in fact is an impact site. Scientists eventually found impact melt which they used to date the crater using Argon-argon dating method at 1.4Myrs.
We tried to remain optimistic our prospects for finding the kind of evidence we needed was fading. Impact craters are very different from other geological structures mainly because of the sudden way they are formed. Most geological processes take place over millions of years. Impact craters form in 1 second. The energy release of a bolide colliding into the bedrock is enormous and the heat generated has an effect on the bedrock that does not take place over geological time. Chuck and I both felt this site had not experienced the cataclysmic changes of an impact site. However the correct approach is to remain open and not make any premature subjective evaluations.
We inspected a talus slope on the outcropping. This is an accumulation of loose rocks which forms a mound. I learned that the angle of a talus slope (angle of repose) is determined by gravity. The higher the gravity the lower the angle of the slope. (The angle of repose plays a role in whether a slope will fail or not. This is the maximum angle at which loose material on this planet becomes stable, usually 25°-40°, and is caused by a balance between gravity and the resisting force.) This explains the difference in landscapes on other planets and moons. Their lower gravity produces geological features with steeper slopes and more pronounced features not possible on Earth. (Note by C. O'Dale - The talus slope I explored at Manicouagan consisted of impact melt with hidden shatter cones. Here at Alsever, the talus slope was Canadian Shield granite, nonimpact related.)
I took pH level readings of the water in the lake at various points. They turned out to be normal at between 6.5 and 6.8. Although these readings were not done with professional equipment they were adequate to the task.
We headed to the junction of Alsever and Roundbush lakes located at the northern end of the site. There is a marsh here that links the two lakes with a small stream. We chose not to try to go to Roundbush because the amount of the effort it would have required.
On the west side of Alsever Lake we found a small spring flowing into the lake. I refilled my water bottle knowing this would be a good source to quench my thirst.
After lunch we continued to inspect the shoreline including two points where the lake flows down towards the Aylen River. Neither point is passable by canoe.
We concluded our exploration late in the afternoon and headed back to camp the same way we came. It is important to plan your day carefully when exploring late in the year because daylight is short in October. We made sure not to head back in the dark. Trails are dangerous at night. Branches can injure your eyes and you can easily get lost. Lake travel is also not advisable at night.
Saturday night was also clouded over and not good for observations. I was disappointed by this because the park offers excellent dark skies. The Moon was nearly full at this time. It rained most of the night till morning.
We broke camp early Sunday morning and skipped breakfast. It was raining and getting colder. The warm sunny conditions we were treated to on Saturday were gone. We hastily loaded the canoe and headed back down the Aylen River. Instead of taking the cart trail back as we had done going up we decided to continue down the river to the point where it intersects at a further point. This was a big mistake.
The river is blocked up with fallen trees and so we had to haul the canoe countless times over logs and through branches. Fortunately the river was shallow most of the way so we could wade through. It took us more than 3 hours to cover about 1.6 KM to the bridge that leads us back to the car. We unloaded the canoe and re-installed the cart wheels in order to pull the canoe and gear back to the car.
Although we did not find any evidence of an impact during our exploration we were satisfied with our attempt.
I have come up with three scenarios for Alsever in terms of it being an impact site.
1. It is not an impact crater but simply has a resemblance to the Brent Crater site.
2. It is an impact crater but evidence has simply not been found yet.
3. It is an impact crater but any evidence of the fact has vanished.
It might be possible to find evidence if drill core sampling was done. This is how the Brent site was proven at a time when drilling was affordable. Today it would be prohibitively expensive to do so. The cost would not validate the expected results even if it was proven to be an impact site.
Our exploration of Alsever has become a treasure of memories for us and a complete success.
If you have any questions regarding this exploration please contact me at: firstname.lastname@example.org
Regards, Eric Kujala
Colter Structure, Oklahoma, USA.
This land formation located in western Oklahoma is approximately 57 meters in diameter. Its circular shape cuts into a slope that consists of varying layers of sandstone/mudstone/shale.The rim is exposed for about 260 degrees of a circle with the rest possibly buried at the down hill side. The rim is illustrated from inside the structure (image left) and on top of the rim looking out (image right).
Descriptions below attempt to describe attributes of specific features of the formation with a pros/cons list to generate dialogue whether the attribute supports the impact theory.
1. Circular shape. As seen from ground level and satellite photos the shape is circular or oval. The angle of satellite photos may distort the shape if not from directly overhead. The rim is only exposed for approximately 260 degrees of a circle. PRO - It would be unusual, especially for this region, for erosion to create a rim greater than 180 degrees. CON - It could be the remnant of an oxbow feature of a wandering stream or creek.
2. Strewn field The strewn field exists mainly to the east of the crater. PRO - Calcite pebbles exist on the surface from the rim to several radii from the crater. The population density of these pebbles decreases quickly with distance from the rim. Calcite pebbles on top surface are different than calcite in veins of the region possibly due to weathering. This strewn field is probably the most fragile of the features because it could be easily disturbed or damaged.
3. Distinct steep sloping face. Face has vertical veins of calcite of various thicknesses. PRO - the angle of the rock face all around the inside of the feature is different from typical erosion of the region. The angle is about 45deg and is consistent all around. Angle isn't supported by root systems. Regional rock creek banks are either vertical or have deep cuts radiating outward.
4. Elevated rim Rim elevation is slight but has protected interior face from erosion by shedding water outward. PRO - Elevated rim could be excavated material CON - Elevated rim could be typical undisturbed shale layers 5. Silt interior Shallow bore holes have yielded only silted in top soil with no shale. No deep holes have been done. PRO - Oxbow would have likely left shale center? CON - Any depression would have filled in with flooding.
6. Shock evidence. CON - No evidence of shock has yet been found.
7. Shatter cones. CON - No shatter cones have been found
8. Meteoric material. PRO - Some material has been found CON - Only tiny stones and dust have been found so far with a magnet.
This area is private property and it is requested that you contact Mr. Doug Massey at (coltercrater at gmail dot com) for information.