Pictured Rocks National Lakeshore
Massive glaciers inched back and forth across this land for a million years, scouring and molding, while the land yielded and took on a new shape. Moving ice ground the volcanic and sedimentary rock of previous eras into rubble and slowly enlarged river valleys into the wide basins that would become the Great Lakes. The last glacier began its retreat about 10,000 years ago. Meltwater from this wasting glacier formed powerful rivers and scattered rubble onto outwash plains and into crevasses. The water scooped out basins and channels that harbor the wetlands found in the park today. Eventually, as the weight of the glacier lessened, the land rose and exposed bedrock to lake erosion. It was this onslaught by the lakecenturies of battering waves and icethat carved the bedrock into young cliffs. Relentlessly the water continues to pound and sculpt the cliffs, eroding them inland while enlarging the lake.
Solid or liquid, the force of the water profoundly altered the landscape and created the largest freshwater lake system in the world. It is hard to visualize that power, until you examine the evidence. You will soon recognize the clues. Look at the water-sculpted arches and profiles of the cliffs. Observe the inland lakes formed when glacial outwash buried enormous blocks of ice. The ice melted over time, forming depressions that filled with water and became kettle lakes. Examine the stones along Twelvemile Beachhorn coral from an ancient sea, polished granite and quartz rounded like eggs, and disk-shaped fragments of the Jacobsville sandstone.
The name "pictured rocks" comes from the streaks of mineral stain that decorate the face of the sculpted cliffs. The ramparts of the cliffs are composed of 500-million-year-old Cambrian sandstone of the Munising Formation. The Munising Formation makes up much of the angled slopes and formations, such as Miners Castle. Closest to lake level is the Jacobsville Formation, a late-Precambrian mottled red sandstone that is the oldest exposed rock in the park. Covering all is the 400-million-year-old Ordovician Au Train Formation, a harder, limy sandstone that serves as a capstone and protects the underlying sandstone from rapid erosion. The streaks on the cliffs occur when groundwater oozes out of cracks. The dripping water contains iron, manganese, limonite, copper, and other minerals that leave behind a colorful stain as water trickles down the cliff face.
Living with Lake and Land
The bounty of the lake and land has attracted people to this area since the glaciers retreated northward. Archaic and Woodland Indians made summer camps along the coast between what is now Munising and Grand Marries. Later, Ojibwa Indians hunted and fished here, as their descendants still do, while en route to their summer fishing grounds at the Sault rapids of the Saint Marys River between Lakes Superior and Huron.
Schoolcraft and Other Adventurers
In the 1600s and 1700s, French and English explorers and voyageurs came searching for furs and minerals. They left little behind except place names, such as Grand Marais and Miners River. In the 1800s, American and European settlers arrived to make fortunes in mining and logging. One adventurer was Henry Rowe Schoolcraft, Indian agent and wilderness scholar. In 1820 he said, "We had been told of the variety in the colour and form of these rocks, but were wholly unprepared to encounter the surprising groups of overhanging precipices, towering walls, caverns, waterfalls... mingled in the most wonderful disorder."
The demand for timber attracted lumber barons who bought vast forests of white pine, beech, and maple. By the 1890s, boomtowns supported sawmills. Grand Marais, bustling with a population of 2,000, produced millions of board feet of lumber annually. Business on the lake also flourished. Wooden-hulled freighters and side-wheelers transported lumber and pig iron to distant markets. To help ships navigate the dangerous reefs, the U.S. Life Saving Service (later to become the U.S. Coast Guard) built light stations along the lakeshore. By the early 1900s most of the forests were gone, and the fortune-seekers moved on. Only a few small towns and lonely lighthouse keepers remained.
Life of the Lake
Measured by surface area, Lake Superior is the largest freshwater lake in the world. It is 350 miles long, 160 miles across at its widest spot, and more than 1,300 feet at its deepest spot, which is about 35 miles north of Pictured Rocks National Lakeshore. This natural vessel holds so much liquid that, if drained, the water would fill a swimming pool the size of the continental United States to a depth of nearly five feet.
Like all things on Earth, Lake Superior is part of an interdependent ecosystem. Picture a giant web with energy flowing from point to point. The spark igniting the web comes from sunshine. Solar energy flows into phytoplankton microscopic plants that turn it into food eaten by zooplanktontiny animals, such as water fleas and fairy shrimp. These are eaten by forage fish, sculpins, and lake herrings, which are eaten by predator fish, such as lake trout. These, in turn, are eaten by bald eagles and other birds, by small mammals, such as otter and mink, and by humans. Humans are an important link in this energy flow because of the "residence time" of Lake Superior's water. It takes 191 years to completely replace the lake's volume of water with an equal amount of "new" water. What humans consume, produce, and throw away will affect the Lake Superior food web for a long time.
Details mentioned in this article were accurate at the time of publication