of the Devil's Kettle
Judge C.R. Magney State Park, the western half of the Brule
River disappears and is never seen again. (Photo
by McGhiever licensed under the Creative Commons Attribution-Share
Alike 3.0 Unported license.)
In Minnesota near the border with Canada sits Judge
C. R. Magney State Park. Named for a local official who was instrumental
in getting state parks and scenic areas established in the region,
the park covers over 4,600 acres of forest along the north shore
of Lake Superior. Flowing south through the park is the Brule
River. The river drops some 800 feet in only eight miles through
a series of waterfalls that delight visitors to the park. After
rolling over these falls, the river eventually enters Lake Superior.
One of these waterfalls, however, is far better
known that the others. About a mile and a half upstream from the
lake is the mysterious Devil's Kettle Falls. At the top of the
falls the river is split into two parts by an outcropping of rhyolite
rock. The eastern half of the river flows over an edge, through
a two-step waterfall, and down into a pond fifty feet below. The
water then continues south along the Brule and out to the lake.
The western half of the flow, however, drops ten
feet into a "pothole," then vanishes completely.
Potholes (or kettles as they are sometimes called)
are not in themselves a really strange geological feature. When
a stream pours over a waterfall, the force of the water can wear
a hole in the rock. As the water swirls around, it can also pick
up small pebbles and sand. Over time these can carve out an elliptical,
kettle or pot-like hole.
Usually the water in a pothole just flows off to
one side through a gap, but in the odd case of the Devil's Kettle
it disappears underground. Where it goes underground, however,
is a total mystery. Scientists who have looked into the enigma
are sure the water either eventually rejoins the rest of the river
or has its own underwater outlet into Lake Superior. However,
every attempt to trace the path of this half of the river has
failed. Researchers have put brightly-colored dyes in the water,
dropped in ping pong balls and other marked objects, but have
never seen any of these emerge anywhere in the area.
typical potholes formed along the Treur River. (Photo
by Ossewa licensed under the Creative Commons Attribution-Share
Alike 3.0 Unported license)
Making the thing even more puzzling is the geology
of the region, which isn't conducive to creating caves or underground
rivers. The type of rock under the falls is rhyolite: a hard,
igneous, volcanic material very similar to granite. Most caves,
however, form in areas with lots of limestone. Limestone is a
relatively soft rock which is easily dissolved by water, especially
if the water is carrying naturally-occurring carbonic acid.
As water seeps underground, it dissolves some of
the limestone, creating a path for even more water to follow.
While carbonic acid is a very weak acid, over time it can dissolve
enough limestone to make a spectacularly large cave. Some caves
support underground rivers large enough to carry a small boat.
However the nearest limestone to Judge C. R. Magney
State Park is hundreds of miles away in southern Minnesota, so
an underground river of this sort doesn't seem to be a reasonable
solution to the mystery.
Are there other ways to make caves without limestone?
Yes, there are. Because much of the rock in the area is volcanic
in nature it has been suggested that the solution to the Devil's
Kettle mystery might be a lava tube.
underground river flows through a limestone cave. (Photo
by Lorenaak licensed under the Creative Commons Attribution-Share
Alike 3.0 Unported license)
A lava tube is a cave formed by lava flowing down
from a volcano. Lava is rock, heated until it becomes liquid.
When it flows it is possible for the lava on top exposed to air
to cool and harden before the lava below does, creating a long,
tube-like structure. When the source of the lava ceases flowing,
the tube can drain out, leaving an empty space. Some lava tubes
can be very large (up to fifty feet in diameter) and long. The
most extensive known example is Kazumura Cave in Hawaii which
is over forty miles in length. Unlike a limestone cave, which
can form thousands or millions of years after the surrounding
rock, a lava tube must form at about the same time as the volcanic
rock around it.
So, the theory is, maybe the water pouring into
the pothole was able to drill down into the rock below deep enough
to connect up with an old, existing lava tube. The problem is
that even though rhyolite is a volcanic rock, it never forms lava
tubes. Lava tubes are usually only created in basaltic rock. There
is basaltic rock deep below the rhyolite at Magney State Park.
The problem is that the basaltic rock down there didn't come from
a volcano. It seeped up out of fissures in the ground and spread
out over a large, flat area like a flood (in fact this type of
rock is known as flood basalt). Because the lava isn't flowing
down from a volcano, lava tubes don't form. And even if against
all odds one did form, the tube would have to be oriented in just
the right direction for the river to take advantage of it, an
example of a lava tube at Hawaii Volcanoes National Park,
Big Island, Hawaii. (Photo by Frank Schulenburg
licensed under the Creative Commons Attribution-Share Alike
3.0 Unported license)
So is there another explanation? Sometimes water
can flow along a fault line. A fault line is a fracture in the
rock caused by the movement of the earth (usually associated with
earthquakes). However, there is no indication of a fault line
in the area of the waterfall. And even if there was, the amount
of water that could flow along it would be relatively small, not
half a river. Also, such a passage would have likely been clogged
over the years as rocks, sand, logs and other materials fell into
the kettle. (There is even a story that somebody pushed an old
car into the kettle and it vanished, but this seems unlikely as
the location is inaccessible by road).
In spring of 2017 a scientist from the Minnesota
Department of Natural Resources (DNR) announced he thinks he's
solved the mystery. Hydrologist Jeff Green beleives he has evidence
that somehow the water almost immediately re-enters the river.
He and colleagues set up water flow gauging equipment just above
and below the falls and found the amount of water going by to
be almost identical: 123 cubic feet per second above and several
hundred feet below it was almost the same at 121 feet per second.
Their conclusion is that the water must re-enter the stream within
that distance. In the fall of 2017 the DNR team will try to confirm
this by putting dye in the water. One concern, with this technique,
however, is that it's been tried before without success.
Until Green's test shows positive results, however,
what happens to half the Brule River still remains a geologic
mystery awaiting some clever person to solve it. The mystery of
the lost river (or half a river) is so intriguing, versions of
the kettle story have appeared in several books and in fictionalized
form in the 2009 movie, Jennifer's Body.
If you want to see these mystifying falls you need
only to take a trip to Judge C. R. Magney State Park yourself.
Observing this puzzling geological feature requires a hike of
over a mile and a climb of 200 steps, but it is an adventure well-worth
Copyright Lee Krystek
2013-2017. All Rights Reserved.