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.
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.
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:
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.
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.
These are pillars of rock separated from the main island and are usually joint controlled
Where wave action erodes and undercuts the base of a cliff.
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***
- 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.
- 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.
- 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.
- 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)
This Earthcache was prepared in consultation with the Apostle Islands National Lakeshore