Some of the best sea
caves of the Great Lakes are located on the shorelines of the
Apostle Islands. You will see caves like no other with arches and
delicate chambers. During the winter one can see magnificent views
of frozen waterfalls and chambers filled with icicles. The Mawikwe
Sea Caves are accessible in the winter over ice or in the summer by
boat or via the Mainland Lakeshore Trail. “Mawikwe” refers to
"weeping woman". It relates to the fact that the bay was once
referred to as "Mourning Squaw Bay" on early maps. The official
renaming of Squaw Bay to Mawikwe Bay happened in 2007.
Geologically the Apostle Islands are a
result of glaciers that once covered this region. They are
originally part of the mainland at the edge of the fault which
formed the depression to which the waters of Lake Superior
collected. When the glaciers melted the water began to shape the
islands. Over time, the waves from the waters of Lake Superior
caused erosion that formed the islands resulting in sandy beaches,
sandstone cliffs containing pillars, caves, and arches. The thinly
bedded, easily eroded sandstones of the Devils Island Formation are
the source of these sea caves, although the bedrock is very old,
the features sculpted from the bedrock are products of recent
erosion.
The Devils Island Formation began over one
billion years ago where rivers carried sandy sediments from hills
in what is now southern Minnesota to a basin where the Apostle
Islands are now found. These rivers carried sediment that slowly
filled the basin, forming a sand flat. The area was covered with
many shallow ponds, some only a few inches deep, connected by
shallow channels. Sand deposits were thinly-bedded, fine-grained,
and extensively ripple marked. Much like the sands of a modern lake
you will begin to discover similarities by examining the “layering”
of the sand on the beach.
Why here?
The Devils Island
Sandstone are thinly bedded, much more so than the overlying
Chequamegon or underlying Orienta sandstones. The thinner the
layering and the weaker cemented sandstones erode much faster.
Control it?
The process of
shoreline erosion in this region is easiest to observe. The sea
caves, landslide scars, and slumped/fallen trees are common both in
the sandstone formations and the red bluffs. It may appear that the
park should take action to prevent such erosion but you must
realize that this process is a natural one of change through time.
Erosion supplies the beaches with sand and provides unique
opportunities to explore all the unique sandscapes.
“At about five in the evening we passed one of the most
stupendous of God’s works and arched wall extending some ways into
the lake, supported by pillars perfect and beautiful bearing on
it’s summit trees of every size and of many kinds, evergreens
entwining their roots in every crevice, mosses growing of every
color, the whole enchantingly sublime.”
Florantha Sproat
describing the cliffs and sea caves at Mawikwe Bay
– April 18, 1842
Erosional Features of the Apostle Islands Sea
Caves:
Arches:
When a number of reentrants join behind the face of a cliff to
other nearby reentrants and leave behind pillars and arches.
Usually a secondary stage of a stack formation.
Joints:
These are narrow cracks in the rock and generally are vertical and
found in sets that are parallel. The joints serve as zones of
weakness that help waves erode more quickly along the joint faces
and play a major role in shoreline erosion.
Stacks:
These are pillars of rock separated from the main island and are
usually joint controlled
Reentrants:
Where wave action erodes and undercuts the base of a cliff.
Caves:
These are produced when a number of reentrants join behind the face
of a cliff, leaving behind supporting pillars and arches. They
develop most easily where the sand layers comprising a rock
formation are very thin.
Access: Parking and trailhead access is
available at the end of Meyers Beach Road; see “Additional
Waypoints” below for coordinates.
***A fee is required to park***
Mainland
- The Lakeshore Trail to the erosional feature is a 1.8 mile
hike or snowshoe, one way.
- When walking along cliff tops remember that this is an
eroding shoreline, and stay back from the edge.
- The trail passes through several ravines, some requiring
stream crossings.
- Please stay on the trail.
- The trail follows the cliff tops and does NOT provide access
into the sea caves.
Boating
- Boaters should avoid sea caves when conditions are
rough.
- Get the marine weather forecast before leaving on your
trip.
- Personal flotation devices (PFDs) should be worn.
- Kayakers should not visit the caves alone.
Winter
- Do not take chances if ice
conditions are unstable. Beware of cracks in the ice even on the
coldest days. Carry an ice bar to test ice thickness.
- Sub-zero temperatures and bitter wind chills are common.
Warm clothing is a must.
- Walking on ice can be extremely slippery- wear sturdy boots
to prevent slipping.
- Watch out for falling ice and rock in and around the cliffs
and caves.
- Please call the Ice Line at (715) 779-3397 extension 3 for
the most current information on access to the Mainland Sea
Caves.
TO LOG THIS CACHE:
1)
Classify and describe this erosional feature that you see at the
given coordinates.
2) Include a photo of yourself near ground
zero.
To log this cache e-mail me the
answer
HERE.
Sources:
- Paull, R.K., and Paull, R.A., 1980, Wisconsin
and Upper Michigan, including parts of adjacent states: highway
guide: K/H geology field guide series;: Dubuque, Iowa, Kendall/Hunt
Pub. Co., xv, 260 p. p.
- Nuhfer, E.B. A Guidebook to the Geology of Lake
Superior's Apostle Islands National Lakeshore: and Nearby Areas of
the Bayfield Peninsula of Wisconsin Fort Washington, PA.: Eastern
National, 1987, 2004 printing.141 Pgs.
- Schultz, G. (2004). Wisconsin's Foundations: A
review of the State's geology and its influence on geography and
human activity. Madison, The University of Wisconsin
Press.
- Apostle Islands National Lakeshore - National
Park Service Pamplet (NPS.GOV)
Links:
This Earthcache was prepared in consultation with
the Apostle Islands National
Lakeshore