IMPACT CRATER EXPLORATIONS

by: Charles O'Dale

PINGUALUIT IMPACT CRATER

Pingualuit crater northern Quebec. The Pingualuit Impact Crater (AKA - New Quebec Crater, AKA - Chubb Crater) is the small dot in the upper right centre of this image. Lake Couture (an impact structure) is visible as the open water to the lower left centre. Age (ma): 1.4 ± 0.1 Diameter: 3.44 km Location: Quebec, Canada. N 61° 17' W 73° 40' Shock Metamorphism: Impactites containing PDF in quartz grains of glassy bombs. Previously called – New Quebec Crater, Ungava Crater & Chubb Crater. “Pingualuit” is the Inuktitut term for skin blemishes caused by cold weather. The Inuktitut word “Ungava” means far away.

In 1943 it was the crew of a USAAF aircraft who first noticed and took pictures (similar to this high altitude image) of a circular structure imbedded in the bedrock of the Ungava Peninsula. Because of the remoteness of the structure, it was only in the 1950’s that geologic expeditions to the crater were initiated. The geologic data gleaned from the many expeditions to this structure, conclusively identified it as a meteorite crater. In Northern Quebec, Canada, there is a pristine simple crater that in 1999 was renamed the Pingualuit Meteorite Crater. It is visible as the small circular structure in the mid-right side of this image, and is larger than the smallest crater on the moon that is visible by telescope from earth. The crater is 3.44 km in diameter with a depth of 400 metres. The lake which occupies the crater is 267 metres deep and it is Quebec's deepest lake. The crater rim is over 100 metres above the surface of the enclosed lake with a pitch of 40 to 45 degrees down to the water. Uplift from the original impact extends outward to a distance equal to almost twice the diameter of the crater. General Area: North of the tree-line in an area of subdued topography in the Canadian Shield. The target rocks are crystalline and some bedrock structure is visible in the north. The area has been glaciated. Specific Features: New Quebec crater is filled by an almost perfectly circular 3 km diameter lake which contrasts sharply with the irregular lakes of the area. Although glaciated, this relatively young structure retains an upraised rim and is surrounded by a faint zone of deformation extending 3 km from the rim. This may be best viewed at low sun angles. The lake has no exterior drainage. This closed system has developed its own local ecosystem, including fish with very large heads, which have adapted to minimal food sources. An intriguing question is how the fish got into the crater lake.

The first expedition to the crater was initiated by a prospector, Frederick W. Chubb, who thought the circular structure was a kimberlite tube and thus a source of diamonds. Victor B. Meen, from the Royal Ontario Museum of Geology and Mineralogy in Toronto, accompanied Chubb on the expedition. During the short preliminary investigation no meteorites (or diamonds) were found among the boulders on the rim or on the surrounding plain. Nevertheless, Dr. Meen felt quite certain that the morphology of the formation indicated that it was caused by the impact of a huge meteorite and not from volcanic action. Dr. Meen estimated that since there were no Inuit legends about the structure, the impact of the meteorite must have occurred at least 3,000 years ago. He named it Chubb Crater after the sharp-eyed prospector.

Topographic documentation of the area around the Pingualuit Crater. Dr. Meen returned the following year in an expedition sponsored by the National Geographic Society. During that return trip he discovered a magnetic anomaly on the crater rim that he thought was due to the signature of the meteorite. This hypothesis has since been proven wrong. It is now known that the majority of the mass of a large meteorite that contacts the earth at cosmic velocity will vaporize upon impact. The resulting explosion will form a circular impact crater in the target bedrock. The Pingualuit Crater from 1500' AGL. Much fuel resource planning was required to enable us to take this aerial image from GOZooM.

Up until 1962, the Pingualuit Meteorite Crater was classified as “only a possible impact crater” based on its morphology. Then Ken Currie, of the Geological Survey of Canada (GAC), found impactites on the raised rim of the crater (at the closest part of the rim in this image). From this discovery, Pingualuit was reclassified as a “probable” impact site. In 1988, Blyth Robertson, also of the GAC, found other deposits of impactites along the south coast of Lac Laflamme (visible in the background to the north in this image). These impactites were transported there by glaciation. The discovery and analysis of these impact melt samples firmly established an impact origin for the Pingualuit Meteorite Crater.

The impact melt rocks correspond to a chemical mixture of some of the local target rocks. They contained mineral and lithic clasts, some of which showed diagnostic shock-produced Planar Deformation Features in quartz. They also contain enrichments in Ir, Ni, Co and Cr suggesting that the impacting body was chondritic in composition with siderophile element enrichment (Grieve 1991). The exposed bedrock of the Pingualuit Meteorite Crater’s target rock consists of a mélange of metamorphosed, Archean plutonic rocks cut by rare basic dykes (Shoemaker, 1962).

The 40Ar-39Ar dating method of the impact melt rocks determined the age of the impact to be 1.4 million years. This places the impact before the first major northern hemisphere continental glaciation in the middle Pleistocene (Grieve 1991). A detailed study of the petrography of the impact melt samples I-86 and II-88 from the Pingualuit Meteorite Crater illustrated the degrees of shock metamorphism affecting the accessory minerals: apatite, sphene, magnetitie and zircon (Marvin 1992).

Bouguer Anomaly gravity studies reveal a profile with a well-defined negative anomaly that is symmetrical with the crater. As was found in the gravity investigations of the Brent, Holleford and Barringer meteorite craters, the negative anomaly field is most likely the expression of low-density fragmental material underlying the crater floor. These craters all produce negative gravity fields due to the low density fragmental rock underlying them and the expanded crustal rocks forming their rims (Innes 1964).

In the 1950’s I saw Dr. Meen on our old black and white TV when he appeared on a CBC television program describing his expedition to the then named Chubb Crater. It fascinated me when he explained the concept that there are many impact craters still recognizable on our planet and I vowed that someday I would visit his crater specifically and possibly the others he mentioned! The Pingualuit Crater is of special importance because its discovery and identification as an impact crater gave rise to the identification of 26 authenticated impact craters/structures on the Canadian Shield (Grieve, 1991).

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Aerial Exploration - August 2001

My dream to visit this crater finally came true with first a trip in my airplane, GOZooM, over the crater followed by a ground expedition.

On the aerial trip over the Pingualuit Crater, I was accompanied by Mr. Terry Peters, a personal friend and flying instructor. A flight to that remote area of the Quebec Arctic is not a trivial expedition and Terry's flying expertise was very welcome. The distance to the crater from Kuujjuaq (formerly Fort Chimo), our only reliable source of fuel in that area, demanded that I make exact calculations of fuel burn, fuel load and payload to ensure a safe flight between available airports. The weather also has to be factored into the planning to ensure a safe flight. Only by carrying extra fuel on board were we able to spend less than 20 minutes orbiting the Pingualuit Impact Crater and safely make it to one of the remote airports in the area (see below for Terry Peters' description of our flight over the crater).

When we initially approached the Pingualuit Crater on my aerial exploration, the structure first appeared as a small hill on the horizon. We were forced to descend to an altitude of 1500 feet above the ground to keep under the cloud layer. When we arrived at the vicinity of the crater, the height of the rim and the depth of the crater were exemplified when the lake that filled the crater suddenly became visible from behind the crater rim only when we were about a kilometer away! What a view! As we gained altitude to get a wider view of the area, we hit the freezing temperature and the windows started to fog up, and this was August! That explained the low cloud layer!

These images of the crater rim illustrate the glacial erosion that has removed the ejecta and some rim material. These images of the crater rim illustrate the glacial erosion that has removed the ejecta and some rim material. It is estimated that the original ground plane was as much as 15 meters above the present level. Even at our altitude the apparent size of the crater was deceiving. To give an idea of the scale, if I stood on the crest of the rim and threw a baseball as hard as I could toward the lake (and I used to make it to home plate from center field!), the ball would only make it two thirds of the way to the water! During my ground expedition to the crater a few years later, I actually did try and throw a rock into the water from the top of the crater rim. The rock maybe got a third of the way down to the water!!

The clarity of the water in the Pingualuit Crater was tested with a Secchi disc and has been documented to have a visibility of over 30 metres! The lake is not connected to the regional drainage system. It is supplied solely by precipitation and is very poor in nutrients. The Arctic Char in the lake are totally isolated from the local lakes and have responded to the consequent malnutrition by evolving oversized heads and thin bodies. In addition to illustrating the clear blue colour of the water, this image shows a “gully” eroded through the crater rim. A hypothesis of how the fish originally “got into” the crater’s lake is possibly explained by this gully. During the times of glacial melt, the water level in the crater was higher than it is today and drained through this gully. Arctic Char may have swum upstream in the creek through this gully and into the crater from one of the local lakes.

This image illustrates the Pingualuit Crater taken approximately 10 km away from the north-west, at an altitude of about 3000 feet above ground. Compare this image with my image of the Barringer Crater and note the difference in the relative size of the craters. I took the images for each crater from approximately the same altitude and distance. The Barringer Crater is 1.19 km diameter and Pingualuit is 3.44 km diameter.

I just could not get enough of this crater. My video and still cameras were constantly active. I was fortunate to have a fellow pilot share the flying chores as I was only looking out at the crater! Documenting this crater was the main purpose of our trip up to northern Quebec.

Our fuel endurance allowed a maximum of 45 minute hang time over the crater. At the 44 minute and 59 second point we headed north-west to the Hudson Strait and the village of Salluit. We picked Salluit to land, refuel and to spend the night because it was safely in range of our remaining fuel. Also, it is one of the most northern villages in Quebec and we wanted to claim that we had actually landed there. Here I am at Salluit refuelling the aircraft from one of the containers of aviation fuel that we transported with us. Without this “fuel stop” we would not have made it back to our point of departure, Kuujjuaq, as aviation fuel was not available north of Kuujjuaq. It is August and yes that is snow in the background!

And we did land with the predicted fuel safety margin. Flying a small airplane in the remote north of Canada requires substantial planning to ensure survival in the event of an “emergency”. In addition to planning in advance for fuel stops, we had more than the recommended amount of survival gear on board. But, when we passed the tree line I thought, “Well, how are we make a fire now with no wood?” Being a member of the Civil Air Search and Rescue organization. I am well aware of the difficulties that are encountered while searching for missing aircraft. In that mode, I ensured that our flight plans were well documented by the authorities. Not only did we precisely follow these flight plans, we made frequent position reports to the “high flying” aircraft far overhead.

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Ground Exploration of the Pingualuit Crater by Charles O'Dale - August 2008

Mr. Eric Kujala, a fellow RASC member, contacted me after he had read my original article (above) to inquire about my future exploration plans to the crater. At our first meeting we agreed to an informal “crater exploration” partnership with our primary desire to eventually expedite a ground exploration project to the Pingualuit Impact Crater. We investigated many avenues for access to the structure, even including walking the 90 km to the crater from Kangiqsujuaq (formerly Wakeham Bay). During the three years that we were investigating ways to get to Pingualuit, we explored many other impact craters. We did this on the ground using Eric’s canoe and, from the air using my airplane.

All our planning efforts changed with the November 2007 opening of the Parc National des Pingualuit. An airstrip was constructed at the crater which meant that we could make it to the crater by simply chartering an airplane from Kuujjuaq. I could not use my airplane for the final leg of this trip due to the weight and fuel constraints caused by the extra bulk of our camping gear. Also, general aviation aircraft are not allowed to land in the park. So in August 2008, after a round-about trip flying in my airplane from Ottawa to Kuujjuaq, then air-chartering via Kangiqsujuaq, we finally arrived at our destination, the Pingualuit Impact Crater. We spent four days of exploration there living our dream.

My accommodations at Pingualuit (crater rim visible in the right distance), securely tied down because of the winds. Our first day at the crater consisted of setting up our camp site and doing a reconnaissance of the local terrain. It was too late in the day for a productive trip up to the crater. I tucked my tent behind a fairly large rock for shelter from the gusting winds (they were steady at 20 knots+). From my camp site the rim of the crater was visible as a small hill in the distance, illustrated in the image. The rocky terrain we had to traverse to the crater is very obvious in the picture. The temperatures here in August ranged from just freezing at night to a pleasant 20° C during the day. The water in my canteen formed ice crystals during the nights.

On the rim of the Pingualuit Crater after an exhausting climb. Now for the exhausting walk around the rim!! Early in the morning of the second day we proceeded up to the crater rim. The walking was extremely difficult with the ground in the area covered in layers with large rock fragments. The rim rose continuously during the 2.5 km walk from Lac Laflamme to the crater. We had to climb over two ridges before reaching the steep slope of the rim itself. The outside rim is covered with a jumbled heap of large fragments of granite blocks. This made it a challenge to safely climb up the 100m, 10° slope. These fragments cover the ground so completely that for a distance of nearly 5 km beyond the rim there is almost no other rock.

After a climb of 100m up the 10° slope we finally made it to the top of the rim. In this picture you can see two very happy explorers savouring the moment, all our planning has finally come true!! The rim is so broad, that at its peak, we could not see the lake inside the crater nor the terrain immediately outside surrounding the rim. The lake within the crater only became visible when we climbed over the flat peak of the rim. From where we stood, it was over 3 km across to the opposite side of the rim. The rim is highest and widest at its north east position giving the crater a lopsided cup shape. On the rim it was perfectly silent, we could hear the waves breaking on the inner rim 150 m below us. The far rim is 3 km in the distance, a challenging hike! The boulders on the slope are very unstable making it unsafe for a descent to the lake at this point. The distance to the water is very deceptive. It looked so close it seemed that you could easily throw a rock into the water from where we stood on the rim. I tried and didn’t even get close to hitting the water!

The hike around the crater took most of the day and I have to say it was not one of the easiest of hikes that I have experienced. There were frequent gullies that we had to traverse along the lip of the rim. Our Inuit guides were extremely helpful in showing us the various unique geological features of the crater. This included leading us to the only safe descent to the enclosed lake. Close to the water we found wild blue berries.

I personally made two trips to the crater during our four day visit. On the other two days I explored outside the rim documenting the effects of the impact on the local geology. The exposed bedrock of the Pingualuit Meteorite Crater’s target rock consists of a mélange of metamorphosed, Archean plutonic rocks cut by rare basic dykes (Shoemaker, 1962). About 5 km east of the crater I was fortunate to find a large example of highly shocked and melted impactite (illustrated in this image - the caribou antler placed on the impactite is for scale). Pingualuit impactite contains enrichments in Ir, Ni, Co and Cr suggesting that the impacting body was chondritic in composition with siderophile element enrichment (Grieve 1991). Pingualuit impactite originated from dike bodies in the crater rim, was eroded and carried 3-4 km north of the crater by water action (Grieve 2006). Being an amateur rock hound, I kept searching for any shattercones that would have been created by the impact, unfortunately without success.

In addition I experienced a close encounter with a few caribou and found an old Inuit campsite. It was impossible to guess the age of this camp site, it could have been here undisturbed for tens or even many hundreds of years! I had a very spiritual feeling gazing at this old camp-site trying to picture the family that survived here. Having had Arctic survival training with the military, and now again experiencing this type of desolate terrain, I stated to our Inuit guides how respectful I am toward their ancestors in that they could successfully support and feed a family in this type of geography.

I also have the utmost respect for past exploration teams who, day after day for months, walked to the crater rim from their base camp for their research. The two trips I made to the top of the crater rim totally exhausted me! Our exploration of the Pingualuit Impact Crater and local area was very rewarding, an experience Eric and I will treasure the rest of our lives (O'Dale 2009).

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"Our Aerial Expedition" by Terry Peters - August 2001

We were off the ground at Kuujjuaq around 3PM with the Chubb Crater, a major attraction (for us!) about 250nm (roughly two hours) away. The visibility was unlimited, except that there was an overcast at around 3000 feet, with only occasional breaks for sunshine to show through. The barrenness of the territory was cause for some reflection. Certainly not a place to be stranded. Caribou tracks were visible all over the place, but not a caribou to be seen. This was about the only disappointment of the whole trip. We never did see a caribou herd. From at least 30 miles we could see the rim of the crater on the horizon. The crater itself was a most impressive sight. It was first recognized as an impact structure in 1950. It’s relatively young - only 1.4 million years and almost perfectly circular, 3.4km in diameter with a raised rim up to 163 meters above the lake surface in the central flooded depression. The lake is 252 meters deep. We must have spent nearly 45 minutes circling it to take photos and video before leaving for Salluit, about 40 min. away. It would have been nice to have landed and visited it on foot but this was a pretty unfriendly and desolate place. Perhaps another time on floats or with large tundra tires!! (we then flew direct to Salluit - author) Terry Peters at a "bilingual" STOP sign in Saluit, Northern Quebec. Salluit (Inuit word for “skinny people”) is situated on a bay surrounded by hills and overlooking Hudson Straight. It’s hard for me to imagine living in such isolation, but the Inuit have lived here for centuries. The airport is relatively new (less than 15 years) so until very recently access was via small floatplanes in the summer or by larger ski-equipped ones in the winter. Ships still bring in supplies during the relatively short ice-free period in the summer. We walked down into the settlement (2 miles or so from the airport - elevation 740ft) on a densely packed gravel road, designed to hold up against the permafrost. The houses are all square, two stories high, shipped in by boat (there are certainly no building materials in this part of the world). They’re placed on shafts that reach below the permafrost. The walls of the second stories are all painted bright blue, green or red, with the ground floor generally white. And all the gravel streets are laid out in neat rows. Would have loved to take pictures of children playing with husky puppies and mothers in Inuit coats carrying babies on their backs, but that would have been rude. It was obvious we were visitors of course and most gave us friendly waves and smiles. Some just ignored us! Several small boats with outboard engines were pulled up on the shore. The economy is based on seal, beluga whale and walrus hunting. A mine 50km from Salluit, at Deception Bay, is a significant player in the local economy. There were three or four pickups, used to carry supplies between the village and the airport. We saw a few 4-wheel dune buggies and one or two mopeds and small motorcycles. About 1030 people live in the village. Some houses are being built a mile or so inland since there is no more room to expand the present housing area. The uphill walk back to the airport gave us more than enough exercise at the end of a long day. Even though it was about 2°C, (and this is August 27th!) we had to take our parkas off! Accommodation in these isolated communities is scarce and very expensive, so we had decided earlier that we would tent. We put it up on the crest of a hill just below where the aircraft was parked on the ramp. The wind snapped away at the tent all night. It rained most of the time but not enough to get rid of the snow patches nearby. In the morning we were fogged in. We used the time to fold up the tent and refuel. Fuel is available at isolated communities but you have to buy a whole 45 gal. drum for $500. Knowing this, we carried an extra 20 gals. with us in 5 gal. containers. Side Note Sugluk Inlet taken from over Hudson Strait looking south. The Salluit village is half way down this fiord on its east coast. The village of Saluit in northern Quebec. In this article I mentioned the village of Salluit, about 200 km north of Lac Couture, where we refueled and spent a cold August night. We arrived there after exploring the Pingualuit Crater and were so impressed with the beauty of the area that I wanted to share it with you. The village of Salluit (right) is neatly tucked into this valley. The airport is on top of the 1000’ hill to the right (south) of the village. You can barely make out the road we walked down to visit the village later that evening. We had a good workout walking back up that hill! The “survival” accommodations that we erected at the Salluit airport, and yes, that is August snow beside the tent! When the sun went down, so did the temperature, to almost 0º C. Yours truly posing beside the "bilingual" STOP sign in Salluit, Quebec "Our Ground Expedition" by Eric Kujala - August 2008 Pingualuit (Where the land rises) is one of the most defined and well-preserved meteor impact craters on Earth. I have noted that it is one of the largest circular objects found on Earth that one can observe with the naked eye from the ground. I first learned about Pingualuit when I was a boy reading a government map of Quebec. I couldn’t help but notice the tiny circle with the words ”Cratere du Nouveau Quebec” written next to it. It fascinated me how this feature stood out on that map. In 2005 I contacted Charles O’Dale to make a trip to the crater. After three years we finally found a way to Pingualuit which we regard as the Shangri-la of impact craters. When I saw the crater for the first time out of the airplane window, I could feel that a colossal and terrifying event had happened here suddenly and with unimaginable force. There were lots of ooohs and aaahhs blurting from the passenger cabin including my own. My next comment was “LOOK AT THAT BOULDER FIELD”. After a skilfully executed approach by our very professional pilots we landed on a dirt strip so short it could have been the deck of an aircraft carrier. Monday morning August 25, 2008, we set out for our first exploration of Pingualuit crater. The walk from the base camp adjacent Lac Laflamme to the north rim of the crater is about a 45 minute walk through a wide expanse of boulders, potholes and streams. It was the most unnerving part of the exploration for me. I am not a hiker. Put me in a canoe and I can go for miles but my hiking experience is limited to portaging. I was thankful the boulders were not wet. In the final stretch I kept my head up and eagerly looked for the top so I could finally see inside the crater. Several more steps and then…..OH MY GOD! Eric Kujala on the rim of the Pingualuit Crater. It was truly a Shangri-la moment for me and Chuck. We were finally looking at the lake and were surrounded by the crater walls. The rim itself is quite wide. I immediately noticed that the rim is eerily quiet. I don’t know if the shape of the crater has this acoustic property but it is one of the quietest places outdoors I have ever experienced. It was thrilling to see Chuck’s 50 year old dream come true. The next few minutes were spent taking videos and photographs for posterity. I saw snowgeese and other birds I couldn’t identify. There were almost no insects. I studied the shape of the crater carefully and observed the different textures and colors which were different from what I had seen in photographs. I crawled on the ground and looked at the miniscule. I smelled things. I reflected on the expeditions which had come here before including Dr. Meen’s. I imagined the Canso aircraft that once landed on Pingualuk Lake. I heard that more recently a Beaver floatplane had landed on it as well. As I sat on the rim looking out, I thought of Fred Chubb, the prospector who thought Pingualuit might be a volcano crater. This is what led him to believe kimberlite and possibly diamonds would be found. I have seen volcanos in Costa Rica and the Phillippines. None of them resembled what I saw on Pingualuit. Rock Ptarmigan and Cottontail can be seen at the base of the crater. There is an abundance of life. The rim however is like a desert because it cannot hold significant amounts of water. There are no trees here. Chuck reported seeing a mouse on the crater rim. The only animals we saw were the caribou which roam the crater. Although they keep some distance from humans they are easily visible and leave many tracks. Pingualuit is neither the largest or the oldest impact crater. It is in fact a very young and small compared to most. When exploring Pingaluit I was able to memorize its size visually so that when I observe lunar craters I can appreciate how large most of them actually are. The smallest observable crater one can see on the Moon with the naked eye is larger than Pingualuit. Unlike most impact sites, Pingualuit is a testament to the awesome force of a cosmic collision. I will never look at the craters on the Moon the same way again. Charles and I have explored many impact sites before. I am thankful to have visited those sites before Pingualuit because I gained much knowledge and perspective on meteor impacts that were helpful in appreciating its unique nature. I would recommend anyone wishing to visit Pingualuit to do some research and possibly visit other impact sites before going there. Impactite from the bolide impact at Pingualuit. The scientific highlight of the exploration for me was the discovery of impact melt. This is the bedrock which melted and fused with the molecules of the vaporized impactor. It has distinguishable attributes. It is vesicular in nature and does not look like any of the other rocks. Impact melt is a good indicator of an impact site. It is important to maintain control over the environmental impact of the park and to avoid contamination. The crater is very fragile. The water in Lake Pingualuk cannot sustain commercial exploitation and must remain untouched. No commercial development of the park can be allowed. It is a unique natural site that I hope visitors in the future will appreciate. The number of visitors must be monitored to ensure the park remains intact. It is the ultimate eco-tourism destination. Thanks to Charles O’Dale I was able to see Pingualuit and my dream also came true. References Grieve, R. A. F., Robertson, P., Bouchard, M., Orth, C., Attrep, M. and Bottomley,R., Impact melt rocks from New Quebec crater. METEORITICS, vol. 26, March 1991, p. 31-39. Grieve R.A.F., Impact structures in Canada, Geological Association of Canada, 2006. Innes, M. J. S., Recent advances in meteorite crater research at the Dominion Observatory, Ottawa, Canada. METEORITICS, v. 2, pp. 219-241. 1964. Marvin, U. B., Kring, D. A., Authentication controversies and impactite petrography of the New Quebec Crater. METEORITICS, v. 27, pp. 585-595. 1992. Meen, V. B., Chubb crater, Ungava, Quebec. Journal of the Royal Astronomical Society of Canada, v. 44, pp. 169-180. 1950. Meen, V. B., Chubb Crater - A meteor crater. Journal of the Royal Astronomical Society of Canada, v. 51, pp. 137-154. 1957. O'Dale, C.P. 2009, Exploring the Pingualuit Impact Crater, Journal of the Royal Astronomical Society, Volume 103 #2, 61-64. Shoemaker, E. M., Geological reconnaissance of the New Quebec crater, Canada. Astrogeologic Studies Semiannual Progress Report, Feb.-Aug., 1961, pp. 74-78. 1962 Shoemaker, E.M. 1962, Astrogeologic Studies Semiannual Progress Report, Feb. to Aug., 1961, 74-78 University of New Brunswick Back to the main CRATER page.