Sunday, November 02, 2008

Minnesota’s Evidence of an Ancient Meteorite Impact

Imagine central North America nearly 2 billion years ago, as a
meteorite 10 miles in diameter strikes the Earth near what is now
Sudbury, Ontario . The force of the collision vaporizes the meteorite and
much of the ground near the impact site, forming a crater more than 150 miles wide(1).
Shock waves race from the impact, deforming the Earth’s crust around the crater’s edge,
and causing earthquakes that shatter the ground hundreds of miles away(2). Within seconds, a cloud of ash, rock fragments, gases, and droplets of molten rock—known
collectively as ejecta—rises through the atmosphere and begins to
spread across the globe. In this turbulent cloud of ejecta, some of the
ash and vapor coalesces—much like hail stones form during thunder
storms—to create small spheres called accretionary lapilli. The lapilli
and other ejecta are propelled from the impact site at supersonic
speeds. In the shallow ocean that covered much of the region, the
impact generates huge tidal waves (tsunamis) that cross the ocean
surface, mixing together rock fragments and ejecta. Over time, this
material is buried by younger sediments, cemented together, and
fused by molten rock to form a solid layer.


In 2007, a layer of rock was discovered in Minnesota that is
thought to have formed during the Sudbury meteorite impact event.
The layer is exposed near GUNFLINT LAKE, nearly 500 miles west
of the impact site at Sudbury (Figure 2). It is sandwiched between
the Gunflint Iron Formation below, and slate of the Rove Formation
above (Figure 3). Both of these formations were deposited as muddy,
oceanic sediments. Nearly a billion years later, these rocks were
intruded by magma (Logan Intrusion) as part of a major continental
rifting event.

Most of the impact layer consists of breccia—a mixture of
fragments broken from the underlying iron-formation and cemented
together (Figure 4). These fragments represent pieces of seafloor that
were ripped loose by impact-related earthquakes and carried down
a submarine slope.

Only the uppermost part of the layer at Gunflint Lake contains
true ejecta—the most obvious of which are accretionary lapilli. Notice
in repeated layering of ash and melt droplets onto the hail-stone like
projectiles. In some of the locations near Gunflint Lake, the lapilli
are intermixed with large iron-formation fragments (Figure 6),
suggesting that the material was reworked by tsunamis.
The impact layer extends discontinuously from Thunder Bay,
Ontario(3), southward into parts of Michigan(4) (5), and westward into
Minnesota (Figure 2). Although it’s a thin layer—only about 25 feet
thick in Minnesota—it’s a very important and remarkable one. Its
importance lies in the record of global catastrophe that occurred in a
“moment” of the planet’s long geologic history and it is remarkable
that such a thin layer has survived weathering and erosion for nearly
2 billion years.

Of the 174 scientifically verified impact structures on Earth,
only one is larger, and few are older, than the Sudbury Impact(1).
For comparison, the Chicxulub Impact on the Yucatan Peninsula of
Mexico, is much younger (~65 million years old) and its crater size
is smaller. Yet, the Chicxulub event caused world-wide extinction
of many species, including dinosaurs. Clearly, the larger Sudbury
impact event would also have had global ramifications.

The internal organization of units within the impact layer at
Gunflint Lake is consistent with the sequence of events outlined
on the table. Seismic shaking from earthquakes deformed and
fragmented the underlying iron-formation, and caused submarine
debris flows that redistributed the fragments into a thick breccia
unit. This was followed by deposition of airborne ejecta that rained
down on the ocean surface and settled to the sea floor, forming the
lapilli unit. Finally, localized reworking of the ejecta and breccia units
by tsunamis produced the uppermost unit of mixed fragments and
lapilli.

Given the preceeding “context for interpretation,” it is an
interesting footnote that the entire layer of breccia and ejecta very
likely represents the catastrophic events of a single day; caught
during the 48 million years that separate the deposition of Gunflint
Iron Formation below from Rove Formation above Table

ARRIVAL TIME EFFECT MODERN ANALOG
1. ~13 seconds Fireball 3rd degree burns, trees ignite
2. ~2-3 minutes Earthquakes Richter scale 10.2 at Sudbury,
buildings collapse at Gunflint Lake
3. ~5-10 minutes Airborne ejecta a layer 1-3 meters thick, with
arrives fragments <1 cm in size
4. ~40 minutes Air Blast Maximum wind speeds ~1,400 mph
5. ~1-2 hours Tsunami None of this magnitude
F
Despite the fact that large meteorite impacts are exceedingly rare
and unlikely in our lifetime, recent geological research demonstrates
that the impact process is fundamental to the formation of terrestrial
planets. The on-going study of these ancient deposits in the Lake
Superior region (Figure 8) will enhance our understanding of the
environmental consequences of impact during the oldest time period
in Earth history.

REFERENCES AND ADDITIONAL RESOURCES
(1)www.unb.ca/passc/ImpactDatabase Website describing 174
meteorite impacts world-wide. Developed and maintained
by Planetary and Space Science Centre, University of New
Brunswick, Fredericton, New Brunswick, Canada.
(2)Dietz, R.S., 1964, Sudbury structure as an astrobleme: Journal of
Geology 72:412-434.
(3)Addison, W.D., Brumpton, G.R., Vallini, D.A., McNaughton, N.J.,
Davis, D.W., Kissin, S.A., Fralick, P.W., and Hammond, A.L.,
2005, Discovery of distal ejecta from the 1850 Ma Sudbury impact
event: Geology 33:193-196.
Figure 8. Electron microprobe image of accretionary lapilli (by McSwiggen and
Associates, PA).
8
(4)Cannon, W.F. and Addison, W.D., 2007, The Sudbury Impact layer
in the Lake Superior iron ranges: A time-line from the heavens:
Institute of Lake Superior Geology, 53rd Annual Meeting,
May 8-13, 2007, Lutsen, Minnesota, v. 53, Part 1-Proceedings
and Abstracts, p. 20-21. Available via website: (http://www.
lakesuperiorgeology.org).
(5)Pufahl, P.K., Hiatt, E.E., Stanley, C.R., Morrow, J.R., Nelson, G.J.,
and Edwards, C.T., 2007, Physical and chemical evidence of the
1850 Ma Sudbury impact event in the Baraga Group, Michigan:
Geology 35:827-830.
(6)Collins, G.S., Melosh, J. H., Marcus, R.A., 2005, Earth impact effects
program: A web-based computer program for calculating the
regional environmental consequences of a meteoroid impact on
Earth; Meteorite and Planetary Science 40:817-840. (www.lpl.
arizona.edu/impacteffects)
(7)Davis, D.W., 2008, Sub-million-year age resolution of Precambrian
igneous events by thermal extraction-thermal ionization mass
spectrometer Pb dating of zircon: Application to crystallization
of the Sudbury impact melt sheet: Geology, 36:383-386.
(8)Fralick, P.W., Davis, D.W., and Kissin, S.A., 2002, The age of the
Gunflint Formation, Ontario, Canada: single zircon U-Pb age
determinations from reworked volcanic ash: Canadian Journal of
Earth Sciences 39:1085-1091.
Or Contact:
Mark Jirsa
Minnesota Geological Survey
jirsa001@umn.edu
612-627-4780 X208
or
Paul Weiblen
University of Minnesota
Department of Geology and Geophysics
pweib@umn.edu
Prepared with editorial and technical support from Barb Lusardi and Richard
Lively-MGS

Friday, June 13, 2008

Echo Ridge (Complete)

Our property consists of 5.5 acres of land with 350 feet of lakeshore. The Gunflint Trail bisects the property, east to west, with approximately 1.5 acres on the south side of the trail, facing the lake. Nor’wester lodge is to our east, Windigo lodge is to our west.
The first deed recorded on our abstract shows George Signalness filed on June 26, 1891, paying the princely sum of $206.15. The property consisted of several thousand feet of lakeshore which was acquired in 1934 by Alice and Carl Brandt Sr. The Brandt’s divided the property into smaller parcels in the early 1940’s, selling to Victor Abrahamson, A. J. Eaton, Frank Arco and Richard & Earnest Heidenrick.

The Eaton parcel, 350 feet of lakeshore and 5.5 acres of land was sold to Arthur and Lucille Berndt in 1949, who sold to Robert and Nell Williams in 1955. The property was purchased by Arnold Longfellow in 1956 for $3,850 and named “Longfellow’s Hiawatha Resort”. It was run on a part-time basis until the new Gunflint Trail divided the property. Longfellow abandoned the resort shortly after that, listed it for sale several times, changed his mind several times, and (luckily for us) agreed to our offer in 1976.

I first inquired about the property in late fall of 1975 upon seeing an ad in the St Paul Pioneer Press. Rarely were northern Minnesota properties advertised in Twin Cities papers. My telephone call to United Farm Realty revealed their offering was zoned commercial and priced beyond our budget.

In May of 1976 I spoke by telephone with the United Farm agent in Grand Marais, Mr. Trygve Hanson, who was eager to show me some properties off the Gunflint Trail. Armed with a blank check and high expectations, I drove alone to Grand Marais to see what was available. Mr. Hanson took me to two places, one on West Bearskin Lake and one on Poplar Lake. Neither was appealing. Surprised to find these were the only properties being offered and already headed back to Grand Marais, I asked about the “abandoned resort” offered in the paper last fall. “Oh, would you like to see it?” Mr Hanson replied. (We have often wondered how well he did in the real estate business).

A quick turnaround had us back at Poplar Lake, having driven past the place on our way back towards town. After overcoming the initial shock of this truly abandoned mess, I surrendered my sanity, signed an earnest money contract, deposited $100 with the understanding the property would be held for 30 days pending inspection and approval of my business partner. My thoughts on the drive back to St Paul were focused on how to artfully present this opportunity to Joan, my compassionate, understanding, loving and adventurous wife. A coward dies a thousand deaths!

In June we met Mr. Hanson and began to explore the abandoned resort (fishing camp) consisting of six sleeping cabins, “main lodge”, ice house across the trail, pump house at lake, two outhouses and shed containing inoperative gas generators, water pump, suspended water tank and lots of parts (to what?) All the buildings had been broken into and ransacked. The windows were boarded up and the doors were padlocked. However, the lodge and cabins still contained beds, bedding, dishes, glassware, cutlery, towels, dry foodstuffs, some pieces of furniture, two gas ranges and a gas refrigerator. Cedar-strip boats, partly submerged, littered the shore. Electric wires drooped between the cabins. Copper tubing curved along an outside wall serving the kitchen sink. Each cabin had a wood burning stove, two burner gas plate, sink basin with drain through the floor, hand made bunk beds, shelf for dishes and a clothes rack. Several large brush piles were prominent. Garbage dumps containing a wide variety of interesting debris were conveniently situated proximate to the cabins. In the ice house across the road, and behind it, was a trove of discarded treasures.

After tramping the grounds and inspecting the insides of all the buildings, our real estate agent gave us the cabin keys and told us to drop them off at his office the next day. “Where can we find a place to get a martini” Joan inquired, fed up with crawling into dark, musty buildings and battling swarms of voracious mosquitoes. Told that Rockwood Lodge, owned then by Don Lobdell and Rick Whitney, was right down the road, we headed for the only spot within 30 miles that had on sale liquor. Civilization at last!

During the 6 hour drive to St Paul the next day, we debated the wisdom of purchasing a “work farm” 300 miles from home, with considerable anxiety directed towards the financial burden of a second mortgage. “Why do I want to drive this far when my dad has a place in Wisconsin we can get to in less than 2 hours” she asked. “Because it’s on the edge of the BWCA wilderness, with no cabins or roads on the other side of the lake” he replied. “The place is a disaster, it’s too far from St Paul, nobody will ever drive this far to visit us, we don’t know anybody up here” she cried. “That’s the beauty of it” he countered, “350 feet of lakeshore and 5.5 acres is a bonanza. Besides, what’s a little work. We’ll fix it up and then just sit back and relax”. “We can’t afford it” she said.
“We can’t afford to let it get away” he said. After much discussion we agreed to buy the place. The down payment was $7000, quite a bit more than we had in our savings account. The mortgage would be $16,500 at 8% interest for 17 years, payments a ghastly $150 per month. Taxes would be $192.07 in 1977. The stage was set to begin our transformation from city folks to “jackpine savages”, one of the best decisions we ever made.

We took possession on the 4th of July, 1976. Our two youngest children, Jeanne 13 and Steven 11, came with us on the first trip. Our two older daughters, Karen 18 and Kathy 17 were more interested in being left home alone. Karen had just graduated high school. Both had summer jobs, neither relished the idea of “working” at the new lake place.

After prying the boards off the windows of the lodge we discovered there was no electricity…none, anywhere. No pole, no meter, no lights. How could this be? Our real estate agent somehow neglected to mention it. Lesson #1 – Caveat Emptor. The sun was shining, mosquitoes by the millions, holes in the screens, broken panes of glass, lots of junk to haul somewhere, who to ask, where to go? After cleaning the main lodge and the two 1930 era gas ranges, Joan started work on the gas refrigerator in the kitchen. “You’ll never get that to run” I said. “Drive down to the place with the store and ask about a dump” she replied. The kids went with me to Trail Service Center where we met GayLynn Liebertz. After introductions she gave me directions to the spring between Leo Lake and Hungry Jack, and to the dump. The spring was our drinking water supply for many years, until we learned that water was available at the Forest Service campgrounds. The dump was one of the best things we discovered in all the years we’ve lived up here. Christened “Aspen Mercantile” by old timer Rolf Huggenvik, the dump served as both a depository for what we discarded and a source of useable materials we found valuable. Best of all, the dump provided entertainment…the bears!

We soon scheduled our trips to Aspen Lake in the evenings when the adult bruins and their off-spring came to dine. Often we had to vie with visitors from the resorts and other cabin owners to find a space at the edge of the dumping area. Our guests considered a ride to the dump (in the back of our pickup) the highlight of their visit. We mourn the advance of trash disposal technology.

The first summer was backbreaking and exciting. We started by gutting the pressed sawdust walls and Masonite ceilings in the lodge, exposing 2x4 studs and rafters, no insulation and piles of dried deposits left by legions of mice and bats. We painted, stained, replaced window panes and screens, burned brush and rotted boats, living by the light of the sun during the day and Coleman lanterns at night. After lengthy discussion with Arrowhead Electric regarding replacement of a pole and meter (Longfellows left without paying their final bill) we finally had electricity in late August. After meeting Carl and Luana Brandt at Nor’wester Lodge we were introduced to Emerson and Jeanette Morris. They spent their summers on the trail, living in their cabin adjacent to Nor’wester with sons Keith and Emerson Jr. When we told Emerson about the water pump in the shed and that we had no idea how it worked, he agreed to come over and take a look. Sections of pipe and couplings were in the pump house at the lake but one piece was missing. Emerson asked if I had seen it. Duh! I had used a short piece of pipe to pry some rocks, not realizing it was part of the pump assembly. Luckily the threads were not stripped. Lesson #2 – everything lying around probably has a use. When the pump and water line were connected and the pump running we heard screams from Joan. The copper tubing in the kitchen, installed in gentle loops with no petcock, had split in several places during previous winters, turning the kitchen into a walk-in shower!

Jeanne and Steve accompanied us on all our subsequent trips, helped with the work, built our first dock and even enlisted the aid of friends whose parents let them go “up north”. They all worked, swam, fished, and had a great time. But Karen and Kathy hadn’t seen the new place. Labor Day weekend saw us all headed north, pulling a borrowed trailer loaded with necessities, many donated by relatives who had things that would be “great for the lake”. Included in the trailer were: beds, bedding, lamps, appliances, tools, (we now had electricity) pop, beer, Weber kettle, charcoal and all the new clothing recently purchased to start school. Why would teenage girls bring almost every piece of clothing they owned you ask? You never had teenage girls! The groceries were in the trunk. We filled the car with gas in Duluth. The summer of 1976 was very dry and burning bans were in effect throughout the state. Joan and daughter Kathy smoked. As we approached Two Harbors I noticed in the rear view mirror what I thought was smoke. I asked Joan if there was a fire in the roadside ditch. She answered no. When I slowed to point out the big chicken statue on the left hand side of the highway, I saw flames leaping from the rear of the trailer. I put the car in the ditch, yelled for everybody to get out and away from the car and fumbled with the trailer hitch, finally getting it unhooked. The trailer was blazing. I moved the car and within minutes the police arrived, followed shortly by the local fire truck. The firefighters had the inferno out in record time. Luckily the tires on the trailer did not burn. After contacting the State Farm agent in town we picked up the blackened, dripping trailer and parked it in a secured area. With no hope of rescuing anything we proceeded to Grand Marais, much to the disgruntled dismay of the girls. They had nothing to wear!

Old clothes from friends at Kimball Creek and a stop at a local garage sale outfitted the teenagers in garb they wouldn’t be seen dead in at home. Less than a perfect beginning to their first look at the new lake place we had renamed “Echo Ridge”. How did the fire start? Possibly one of my smokers tossed a cigarette out the window and it landed in the trailer? Or perhaps someone in a passing car? An unsolved mystery since neither of my suspects ever confessed. The older girls survived the weekend, helped with the dirty work in their new, old clothes and accompanied us to Windigo where we all became friends of the Ekroot family and the Saint Bernard dogs.

On the trip home we picked up the trailer, unloaded all the burnt debris at the Two Harbor’s dump, salvaged some tools and, miraculously, a 14K gold necklace and several pairs of brand new earrings. I paid for the materials, helped rebuild the trailer and was allowed to use it many more times in the following years. Lesson #3 – be thankful for good friends.

In October we hosted Joan’s parents, two of her brothers (Ron and Jack), Jack’s wife Katie and their infant son Andy. I roofed for the first time in my life during their stay, wisely choosing to begin on the back side of the lodge where the wavy shingle lines were not obvious. It snowed! We had a turkey dinner and pretended it was Thanksgiving Day.

What we have experienced in the 31 years since buying our lake home is nothing short of wonderful. We learned early on that Echo Ridge is not too far for visitors from the cities to travel, and we had cabins and beds for them to sleep in. Although the lures we dangled were canoeing, fishing, hunting, wildlife (moose, bear, grouse, Windigo), great meals and occasional beverages, what we really angled for was a volunteer (low cost) workforce. This was willingly provided by our kids and their pals, good friends, and most notably the Lachenmayer clan, our main source of help; technical, physical, emotional and comical. Sweat labor was the most common form of summer entertainment, enhanced by the constant attack of black flies and mosquitoes. Summer started in May when the lake opened and ended in October with “Honeymoon Weekend”, the no-kids-allowed hiatus for grown-up siblings, where the only labor beyond cutting and splitting firewood was the futile efforts of the guys trying to best the girls in Trivial Pursuit.

We have enjoyed the visits of not only relatives and friends, but also former owners of our property and families who vacationed here before we bought it.

We’ve yet to achieve our original goal to stop working and just relax, but we don’t do as much every day as we did in the early years…our energy levels aren’t what they were. The Morris family became our close friends, sharing recipes, stories and even secret spots to pick blueberries. Jeannette became Joan’s “north shore mother”. Emerson and Keith did all the major renovations to our buildings; moving cabins, designing and remodeling interiors, building our garage and upgrading the outhouses, cutting off the end of the main lodge and creating a bathroom and kitchen with indoor plumbing.

Since his parents’ passing, Keith has continued to be our builder. Working with Bob Johnston and Bob Olson they recently converted the original generator shed into a laundry room. After 28 years using the machines at Nor’wester and Windigo, Joan finally has her own washer and dryer.

Adversity tempers the steel of north woods property owners. We have endured the onslaught of army worms and tent caterpillars, survived the wrath of the “Blowdown”, overcome a frozen septic system, lamented the diminishing population of walleyes, seen lake levels fall and wondered why the snow doesn’t. We have watched in horror as fires burned thousands of acres of our beloved forests, destroying homes and businesses. We count ourselves blessed that our property has been spared. We love it up here because it is a unique treasure. We have wonderful friends and neighbors who share our affection for all the things Cook County and the Gunflint Trail offer. Many of the property owners we have met or heard about during our years at Echo Ridge have stories to share that make ours pale in comparison. We are first generation land owners who stand in awe of the pioneers who developed this area and we are deeply indebted to them for their sacrifices