My exploration and documentation of craters (presently only on this planet).
BRENT IMPACT CRATER – GROUND EXPLORATION – #1
Ground Exploration of the Brent Impact Crater – Part I
To follow our ground explorations of the Brent crater, please refer to this image where I have traced out the path of our explorations.Barry, Chuck and Dale fresh and ready for a day of Brent crater explorations.
Not being satisfied with aerial explorations of the crater, I just had to visit the feature on foot for a full appreciation of what happened there. At one of my Ottawa RASC presentations I mentioned my plans and offered a day of adventure for anyone who wished to accompany me. Barry Mathews and Dale Morland expressed an interest and before you knew it we ( L-R Barry, Chuck (author) and Dale) were standing at the observation tower (position #1 in the crater tour image) beginning our adventure at the Brent Crater south rim. Tecumseh Lake is visible over Barry’s right shoulder. We planned the tour for mid-spring 2003, to avoid the bugs. Also, some of the swamps would still be semi-frozen, allowing us to explore areas that would normally be isolated in the summer because of the bogs. The exploration trip I had planned had a few “off trail” segments.
The Brent crater taken from the observation tower looking north. The northern rim of the crater is clearly visible in the distance.
In image at left taken from the observation tower (position #1) the Brent Crater is visible to the north and northwest. The far rim, about 4 kilometres away, rises about 150 metres above Tecumseh Lake which is visible at the right (north east) in the image. Gilmour Lake is hidden behind the glacier sculpted sedimentary fill visible as the small wide hill in the mid background. Later that day we were going to be standing on top of that hill. As we later found out, this view from the tower is the best view of the crater we would see from the ground.
A typical creek in the Brent crater. I explored these creeks trying (unsuccessfully) to find in situ impact breccia.
From the observation tower we followed the trail down the south east rim to the crater floor and saw plenty of wild life tracks in the snow. Some of the tracks were pretty big! That’s OK though, I think I could out run the other two guys!? Near the bottom of the rim a little creek has carved out a gully in the soft gritty limestone rock material that is not found anywhere else in the Park (position #2). This rock was formed when erosion of the crater rim built up a pile of fallen rock fragments called talus (the fossils of the Burgess Shale are also encased in talus). The sharp edges of these rocks were slowly rounded off by wave action of the sea water that partially filled the crater during the Devonian period. Mud filled the spaces between the fragments and eventually solidified into gritty limestone. The original talus fragments are now imbedded in the limestone. The ferns that grow here are “bulblet bladder fern,” a species common in the limestone areas of southern Ontario, but not found anywhere else in Algonquin Park.We followed the trail down the south rim to the bottom of the crater (position #3). The hiking was not difficult on the trail. Fortunately for us, the original 45° angle of the crater rim had long since been eroded to a semi-gentle slope.
Over 400 million years of erosion had erased 220 metres of bedrock, the bowl shape of the impact crater is still visible. At higher altitudes the three dimensional feature of the crater is difficult to resolve which probably explains the relatively recent recognition of this crater. Maps published as late as 1946 do not accurately depict the two lakes in the crater.
Here Dale and Barry are on the southern crater rim bottom, about 1 metre above the crater floor. Note the vegetation in the background, not too thick and fairly easy to navigate through.Looking 180° from the previous photo onto the crater floor is yours truly (still at position #3). Note the vegetation in the background, the horizontal visibility in there is 4 or 5 metres at the most. That is where we are headed next for the “off trail” portion of our exploration! Even though the swamps were still semi-frozen with lots of remaining snow, we still got wet up to our knees!Ground zero at the Brent crater. Glaciers sculpted the area between the two lakes with a “ripple” superimposed on the landscape.
Why did I want to trek through that swamp and cedar grove? Why, to get to ground zero, the area of the original meteorite impact! I took this image in the winter from less than a thousand feet above the crater floor and thought “what a great view of the crater it must be from that point!” Tecumseh Lake is on the right (east) and Gilmour Lake is on the left (west). In the bottom (south) of the image is the edge of the swamp that we slogged through. The visibility was very restricted while we were in the swampy cedar grove and it would have been very easy to get disoriented in that mess. Note how the last glacier has sculpted ripples into the sedimentary fill between the lakes.
On the ground at ground zero in the Brent crater. (Do you think we are here….or there…??)
It was a good thing that the sun was out as had I forgotten my compass! Keeping the shadows in the correct relative place prevented us from being lost, well not much anyway! Like in this image, “I think we are here!?” Actually, we are at ground zero (position #4) in this image planning our return to the trail (and we did find it first try!). Here 390 million years ago an object 150 metres in diameter impacted with a velocity of at least 11 km/sec. If we were there at the time of impact, we would not have heard the approach or knew what hit us.
This is another image at ground zero looking south west (position #4). Great view EH? We couldn’t see anything of the crater! But at least we could say that we stood exactly at the position of impact! Barry and Dale are in the background with a very strange tree formation in the foreground.
We had stopped for a snack break. The majority of trees here on the sedimentary fill mound were deciduous while the trees in the swamp and on the rim tended to be coniferous.
We made it back to the trail from ground zero without too much trouble and stopped here at the south edge of Tecumseh Lake (position #5). From here years later, Eric and I will expedite a canoe exploration of the crater AND I WILL FINALLY FIND IMPACT BRECCIA!
Tecumseh and Gilmour Lakes have the highest concentration of bicarbonate of any lake in Algonquin Park. Bicarbonate is derived from calcium carbonate which is limestone. Gilmour and Tecumseh, alone among Algonquin Park lakes, are lying on Devonian limestone bedrock. This limestone would not be here if it were not for the bowl of the crater where it collected and was protected. In this marsh at the edge of the lake pitcher plants grow. They trap bugs to enhance their diet which is deficient due to the nutrient poor soil.
Following the trail and climbing the south rim we arrive at the only bedrock outcrop we were to find (position #6). This shattered bedrock has the characteristics of rock exposed to a nuclear blast or a meteorite impact.
I think we can eliminate the possibility of a nuclear explosion happening here 396 million years ago! The force of the explosion is estimated to have been equivalent to the explosion of 250 megatons of TNT. I was fascinated to see the effect first hand, a wall of bedrock with this amount of damage!
At the end of the trail is a mail box with a log book inside. We signed and dated the book and found that we were the first explorers of the crater for 2003!
Normally the ground tour of the Brent Crater would be complete at this point. But I noticed on the topographical maps that the highest point of the crater rim is on the north east portion of the rim and is accessible by road. Well, we just have to go and see the great view of the crater from up there and it would be a pleasant drive! Unfortunately snow had blocked the road and we were forced to “foot” it (position #7). Well, after about a 3 kilometre walk (through snow and mud) we made it to the highest point on the crater rim and you can see from this image the great view we had!
The highest point of the Brent crater rim. If you look carefully in the center of the image you can almost see Tecumseh Lake. The haze on the horizon in the background is the west crater rim. From this point if you tried to walk downhill toward the crater for a better view the relative tree level goes up and blocks the view. From the sun angle you can tell it is getting late in the day, a full day of hiking!Here Chuck and Dale are proudly standing at the highest point on the crater rim (position #8), a big two thumbs up! The rocks visible underfoot are all glacial till from who knows where!
Oh well, at least we can claim that we had stood at the highest point on the crater rim as well as at ground zero (position #4). Reflecting back on the distance we walked to explore the crater has given us an appreciation of the energy that was required to create this crater in a matter of seconds!
After a long slog back to the van, we headed home to Ottawa. What a great day!
