Dr. Firestone wrote:
“The other argument against the YD impact is that there is no crater near the Great Lakes. That is not necessarily true. The second deepest terrestrial place on earth is the Lake Superior basin and the basins of three other Great Lakes are deeper than Death Valley despite lying in
the flat Midwest far from major tectonic activity. The mid-Continental rift might explain the Lake Superior basin but the other basins propagate perpendicular to that old fault.”
Unfortunately, the arguments that the Great Lakes are impact craters of some sort is so completely and readily refuted by such an enormous amount of published sedimentologic, stratigraphic and chronologic data that all they do is confuse and muddy the discussion about the Younger Dryas impact hypothesis in a very prejudicial
manner. It is now very well established that neither terrestrial impacts nor tectonism associated with long
inactive Precambrian rifts or any other faulting had any role in creating the Great Lakes.
Basically, the Great Lakes were created by the preferential erosion of weaker strata within the Great Lakes region,
including Paleozoic strata outcropping around the edge of of the Michigan Basin. The precursors to the Great Lakes
were a series of preglacial river valleys that were deeply entrenched into and followed these outcrops belts. These
valleys existed before the beginning of continental glaciation in North America over 2.5 million years ago. Over
the last 2.5 million years, these valleys have been further deepened and widen by at least 11 different continental ice
sheets. While working on my MS at University of Illinois, I have personally seen some of the enormous amount of rock material excavated by glaciers from the Great Lakes that now comprise large parts of thick Wisconsinan, Illinoian, and Pre-Illinoian glacial tills that cover large parts of Illinois and other states. There is an overwhelming
amount of published evidence and data, including seismic and cores from the Great Lakes, that shows that they
predate the Younger Dryas in some form by tens of thousands, hundreds of thousands of years, and over
a million years and are largely glacial in origin. On the other hand, there is a remarkable lack of data that supports
the occurrence of such a cataclysmic event. Saying that the Great Lakes are the result of an extraterrestrial impact is
the scientific equivalent of the recent “paper” by Zysman and Wallace in the arXiv.org archive that claims drumlins
and eskers were created by extraterrestrial impacts.
Hough, J. L., 1958, Geology of the Great Lakes. Urbana, IL:
University Illinois Press.
Hough, J. L., 1963, The prehistoric Great Lakes of North
America. American Scientist. vol. 51, pp. 84–109.
Larsen, C. E., 1988, Geological history of glacial lake
Algonquin and the upper Great Lakes. United States
Geological Survey Bulletin no. 1801.
Larson, G., and R. Schaetzl, 2001, Origin and evolution
of the Great Lakes, Journal of Great Lakes Research.
vol. 27, no. 4, pp. 518–546.
Spencer, J. W., 1891, Origin of the basins of the Great
Lakes of America. American Geologist. vol. 7, pp. 86–97.
Also, I have the PDF file of a 1993 Midwest Friends of
the Pleistocene field trip, which discusses the glacial
geology of the Door Peninsula at:
It summarizes what is known about the geology and
history of this part of the Great Lakes. Despite over
a century of research in this part of the Great Lakes,
nobody has either found anything remotely resembling
impact ejecta or impactites in the local Quaternary
sediments or any evidence of shock metamorphism
in the local bedrock.
On the same web site, I have some reprints of papers
on impact-related topics.
Dr. Firestone noted:
“A smaller crater Charity Shoal in Lake Ontario has been
identified and is of the correct age.”
The Charity Shoal feature is a fascinating landform. It is
a clear and obvious candidate for an impact crater. However,
it has been badly eroded by glacial erosion and is partially
filled with glacial till. Given that the last time that this part
of Lake Ontario was covered by the Laurentide Ice Sheet was
about 12,500 BP C14 (14,500 BP calibrated), it was almost
certainly created before the proposed Younger Dryas event.
If these remarkable feature has been directly dated, I would
be very interested in a citation for where the date(s) and
dating methodology for this feature has been published.
In a similar vein, at 11,000 BP C14 according an abundance
of glacial deposits and radiocarbon dates, Lake Superior was
still filled by the Laurentide ice sheet. This complete refutes
the notion that the formation of any part of it was associated
with the proposed Younger Dryas impact. In another case, the
floor of the eastern part Ontario contains a field of very well
preserved drumlins. Given that this part of Lake Ontario was
last filled and modified by the Laurentide Ice Sheet about
12,500 BP C14 (14,500 BP calibrated), it clearly predates
the start of the Younger Dryas and existed and was last
modified by glacial processes long before any Younger
Baton Rouge, LA 70803
From Steve Dutch following Heinrich’s email above:
“These arguments were all concocted to explain the unexplainable. Water and ice don’t flow downhill anywhere in the world forming holes 1300 ft deep in a nearly flat terrain. The evidence that the bedrock there was broken up by early volcanism is also explained by an impact. Dating the Great Lakes is impossible following an impact because the historic record is blown away. The earliest research on the Great Lakes could find no explanation for their Great Depth. The current research failed to even consider an impact event. Drumlins, eskers, and pot hole lakes may all have been formed in conjunction with the impact.”
Paul Heinrich’s remarks are dead on target. The axes of lakes Michigan and Huron follow the soft belts of Devonian rocks, which is why the lakes are concentric around the Michigan Basin. Green Bay and Georgian Bay are excavated in soft Ordovician shales. The Door Peninsula, Manitoulin Island and Bruce Peninsula are the edge of a resistant Silurian escarpment.
Was Great Slave Lake also excavated by impact? It’s over 2,000 feet deep, (1500 feet below sea level) the deepest lake in North America. Great Bear Lake has a bottom 800 feet below sea level. How about Lake Chelan in Washington, a narrow lake almost 1500 feet deep, with a bottom 400 feet below sea level? Lake Washington, east of Seattle, has a bottom nearly 200 feet below sea level. Loch Ness in Scotland extends 750 feet below sea level. Lake Ladoga, Russia, extends about as deep, and Lake Onega nearby extends 280 feet below sea level. Lake Garda in Italy has a bottom nearly 1000 feet below sea level. Lake Vanern in Sweden goes 200 feet below sea level and Lake Vattern 120 feet. Lake Champlain goes 300 feet below sea level. Lake Te Anau in New Zealand: 700 feet below sea level; Lake Wakatipu, 300 feet; Lake Manapouri: 800+, and so on. Notice these are all in glaciated areas.
Glaciers can and do erode deep basins in level terrain (and north of Lake Superior is not flat). Maximum erosion seems to take place several hundred kilometers behind the maximum ice advance. Glaciers are not constrained like water because the dome profile of an ice sheet allows outward flowing ice to move downhill and push ice out of any basin. If the ice surface in Canada was 3 km above sea level there is plenty of driving force to push ice into and out of Lake Superior. Anyway, a true scale cross section will show that the upward gradient out of any of these glacially excavated lakes was not terribly steep.
I have been to thirteen impact sites. Any impact large enough to excavate a basin the size of one of the Great Lakes will produce abundant shatter cones and large volumes of impact melt and breccia. It just isn’t here. We have shatter cones at the dinky little Glovers Bluff impact in central Wisconsin (10 km diameter, max). Why aren’t they all around the Great Lakes?
Steven I. Dutch
Professor, Natural and Applied Sciences
University of Wisconsin-Green Bay
Green Bay, WI 54311-7001
Phone: 920-465-2246, Fax 920-465-2376