117. Tettegouche State Park (Palisade Head)

300-foot sheer cliffs of weather-resistant, silica-rich pinkish rhyolite flows overlooking Lake Superior.

The geology of Palisade Head Click to open side panel for more information within Tettegouche State Park Click to open side panel for more information is defined by ancient volcanic activity, cooling structures, and differential weathering along the North Shore of Lake Superior.

1. Tectonic Origin: The Midcontinent Rift System

Age: Approximately 1.1 billion years ago (Mesoproterozoic Era).
Volcanic Setting: During this era, the North American craton began to split apart along the Midcontinent Rift System (a 2,000 km-long continental rift zone). Massive volumes of molten rock erupted along the Lake Superior basin, forming what is now known as the North Shore Volcanic Group.
Felsic Magma: While most lava flows in the region produced dark, iron-rich basalt (mafic rock), localized pockets of silica-rich (felsic) magma reached the surface, producing rhyolite lava flows.

2. Composition: The Palisade Head Rhyolite

Rock Type: Palisade Head is composed of porphyritic rhyolite, a fine-grained, reddish-to-pink volcanic rock containing visible crystals (phenocrysts) of quartz and orthoclase feldspar.
Thick Flow Unit: The eruption that created Palisade Head was unusually massive for a felsic flow, reaching thicknesses between 200 and 310 feet (60–95+ meters) and covering an area several miles across.

3. Cooling Structures: Columnar Jointing

Column Formation: As the thick, viscous lava cooled slowly from both the top and bottom, contraction caused the rock to fracture into vertical, polygonal columns (columnar jointing).
Visible Prominences: These steep vertical columns form the dramatic, sheer cliff faces visible today at Palisade Head and nearby Shovel Point.

4. Differential Weathering & Glaciation

Silica Resistance: Rhyolite contains a high concentration of silica (SiO2) and very little iron compared to neighboring basalts. This chemical composition makes rhyolite far more resistant to chemical oxidation and mechanical breakdown.
Glacial Scouring & Wave Erosion: During the Pleistocene ice ages, massive ice sheets scoured the Lake Superior basin, easily eroding the softer surrounding basalts while leaving the hard rhyolite standing tall. Glacial plucking and continuous wave action along the vertical columnar joints carved out the sheer cliffs that rise over 300 feet above the lake.

5. Inland Reach in Tettegouche State Park

River & Waterfall Formation: The Palisade Head Rhyolite unit extends inland into Tettegouche State Park Click to open side panel for more information , where its erosion-resistant ledges cap several waterfalls along the Baptism River, including High Falls.