Geologic Formations

Capes and Cliffs
Many visitors to Kenai Fjords National Park take a boat trip out of Resurrection Bay to see the wildlife, glaciers, and scenery. On the east side of the bay, Cape Resurrection presents a massive, sheer cliff to the pounding of the waves. The bubbled texture of the cliff, ideal for nesting birds like black-legged kittiwakes and horned puffins, is igneous: lava that bubbled up underneath the water and cooled quickly, forming pillow basalt.

On the opposite side of the bay, the shore is eroded into spires, cliffs, and coves. Exposed areas reveal buckled layers of ancient sediment. Mud, transformed by heat and pressure, becomes shale, a fine-grained, dark-colored stone with many thin layers; more time, more pressure, and the shale hardens to slate. If there is sand mixed with the original mud, it may become greywacke instead. These softer layers crumble into the sea more rapidly than basalt. Arches and spires form from the erosive action of waves.

As you round the corner to the west, moving out of Resurrection Bay, Cape Aialik juts into the tumultuous water. Here is granodiorite, part of a massive pluton that extends down the shore, cropping up again at the entrance to Northwestern Fjord. Granite is lightercolored than the ocean sediment rocks. It is more resistant to weathering, more resistant to the action of glaciers upon its surface. Where glaciers have carved the bedrock into impossibly steep cliffs, the slate crumbles once the ice melts away; but the granodiorite stands, the sheer surface draped with waterfalls.

Cliffs and islands of greywacke, like Nuka Island, have virtually no seabirds nesting on them as their softer surface is too easily eroded to make a safe home. Granitic islands, on the other hand, are packed with birds. The Chiswell Islands, pinnacles of granodiorite stretching up from the sea floor, are home to tens of thousands of puffins, murres, and auklets. Birds seem to have an affinity for granite—one of many ways that bedrock influences the life found on its surface. Sea lions, too, congregate on smooth granitic slabs washed by ocean swells to mate, give birth, and rest.

 

NPS Photo by Paul Ollig

Quartz seams

Seams So Real
The bedrock of Kenai Fjords National Park has been carried north by the action of the tectonic plates. It has been heated and pressed into a new form. It has also been broken. The fractures in the rock filled swiftly with jets of superheated water from deep in the Earth. The water carries dissolved minerals such as iron, silica, arsenic, gold. These precipitate out, forming white and brown streaks across the darker bedrock.

As park glaciers retreat, more bedrock is exposed. Signs of past events are visible in the white seams of quartz shooting through the dark greywacke and in layers of upended slate silently pointing to the slow, inexorable compression of plates. Ice has left its scouring marks across every surface. Yet these signs of the past are quickly engulfed by a wave of verdant life racing across the landscape, filling every conceivable niche, and rushing forth to hide the larger forces at work.