The island itself is a series of SW/NE trending asymmetric linear ridges. The rock on the northwest side of the island steeply drops into the cold waters of Superior while the rock on the south side gently slides into the breadth of the lake. There are two main rock units found on the island.
The Portage Lake volcanics formed during an episode of volcanoes that extruded flood basalts during the Precambrian (about 1.1 billion years ago). The northern two thirds of the island is comprised of various textured basalts. These textures (opitic, porphorytic, pegmatic, etc.) are a result of the environment that the rock crystallized. Copper and secondary minerals like prehnite, greenstone and agate filled the voids that fractures and gas bubbles left.
The southern third of the island is composed of a unit known as the Copper Harbor Conglomerates. Deposited in streams, this sedimentary rock unit looks like a bunch of pebbles and sand compressed and cemented together.
To understand the origin of these two rocks we have to think big. Over a billion years ago Earth was still "figuring itself out". The beginnings of the North American continent had formed. However, this mass was unstable and found itself rifting apart down the middle. Magma from deep within the Earth began to dome upwards as the rifting thinned the surface. This magma found its way to the surface and lava flowed on the surface and in shallow water (think about the volcanoes of Hawaii).
When billions of tons of heavy, dense iron-rich volcanic basalt oozed to the surface the weight depressed the crust. The area around the rift began to warp downward. Soon a syncline (basin) was formed. Water, always opportunistic, found this relatively low basin and began to flow into it carrying sediment from the highland areas around it. As a result conglomerates and other beds of siltstone and sandstone were deposited atop the basalts of the Portage Lake Volcanics waiting for us to explore.
Since then four major episodes of glaciation and closely associated changing water levels have carved out the Lake Superior basin and the landscapes that we see today.
Prehistoric people discovered the island and prized it for it's obvious copper wealth. Over one thousand prehistoric mining pits have been documented on the island. Apart of it's minerals, Isle Royale was also an important source of wild rice, berries and wild game.
Three major mining booms have since occurred on the island. The hard work of "blast and dig" mining never proved economical successful and most operations failed without profit. Many pits and abandoned equipment can still be found throughout the island.
Commercial fishing was also a vibrant part of the island's history. Isle Royale's unpredictable topography and reefs are wrecked many ships on it's notorious shoals. A hand full of lighthouses round the island's perimeter and light it's passages.
Isle Royale is now the stage of the dynamic saga for one of the most hailed predator-prey relationships in the world. For more than 50 years, biologists have been watching the delicate interactions between the grey wolf and moose. Moose probably swam to Isle Royale around the turn of the 20th century. At any given year about 1000 individual moose have inhabited the island feeding on the plentiful vegetation of the the island's wetlands. At one point, moose became too abundant. The island's vegetation wasn't enough for the booming population. A die off ensued. Sometime around 1940 wolves crossed from the mainland on the winter ice. Since then the two species have been tangled in a natural exhibit of capable predators killing the weak and old. Today just under twenty wolves inhabit the island.
Now the least visited National Park, Isle Royale is an amazing place to visit. 80% water, one can sail, fish, hike or paddle it's beautiful landscapes. My only qualm; it should be considered a part of Minnesota not Michigan!
Sunset over Blake Point. The northern most point of Isle Royale.
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