Rock formations on the beach have a story to tell

Rock formations on the beach have a story to tell about the surficial geology o the Kenai Peninsula.

I like rocks. I like big rocks and little rocks, flat rocks that skip and large rocks to sit on. I like rocks in mountains, rocks in rivers and tiny tidbits of rocks ground up on a beach. I love examining the minerals in rocks such as white feldspars with their perfect planes and jet black biotite crystals that make chunks of granite sparkle. I find metamorphic gneiss mighty nice with bands of minerals formed by really high pressure and heat altering the parent rock. I even like grey rocks like shale that break apart easily and hard chucks of plain old basalt that are simply heavy and grey. In fact, I never met a rock I didn't like.


Even if you don't share my enthusiasm for these specimens, chances are you, too, have picked up a rock or two at some point. Maybe it was the shape or the color or the sparkle. Maybe it was a source of frustration when you were digging a hole. Maybe you needed a paperweight, a doorstop, or an impromptu hammer. Whatever the reason, if you stopped to look, you might have noticed that rocks are everywhere. And the point is ...?

I am going to let you in on a little secret. Aside from the aesthetics of rocks, there's another reason I enjoy geology. Rocks are like words, and together they tell a story. Learn to read the words and suddenly a walk down along the Kenai River becomes more than just a pretty view.
This story is quite complicated and it has a lot of chapters. Some of them are so big you would need to step far away to see them. For example, the earth's surface is made of moving tectonic plates. Currently, the Pacific Plate, including parts of California west of the San Andreas Fault, is slowly being subducted under southern Alaska.

Movements like these can cause tremendous pressure that translates into the formation of features such as mountains (subduction zones are great places to find volcanoes if you happen to be hunting for one). Within these large stories are pages of smaller stories -- ice ages in which glaciers carved the earth's surface and windblown sand built dunes.

By looking at the geology right under our feet we can begin to piece together a history of the area. How did the Kenai River get where it is today? Where did the big boulders on the beach come from? The answer to the former is a little too complicated for this article.

The answer to the latter is glaciers. Giant sheets of moving ice grabbed these massive rocks (plus some rocks of other sizes) and carried them along. Then, conditions changed and the ice started to melt. As the ice retreated, miles of deposits were left behind. Massive boulders such as those on the beach are called glacial erratics and are composed of rock types foreign to their present surroundings. By mapping the location of these glacial deposits and landforms we can start to visualize the passage of glaciers.

Knowing where glaciers were might be fun if you like history or have particular interest in ice, but is this useful? You might say "no." Who cares where a bunch of ice was sitting a long time ago? Why bother trying to map all those piles of rocks and dirt? Well, it turns out knowing what these surface deposits are and where they lie IS important.

The surficial geology (the loose, or sometimes solid in the case of lava, deposits on the earth's surface that were laid down during the Quaternary, a period spanning the last 2.6 million years) in this area includes sand dunes, swamp material, marine deposits, beach, glacial and river materials, just to name a few. Knowing this parent material can help us determine if the ground in an area will be stable enough to build on, model how water will move through the subsurface, determine how well the ground will drain, evaluate what areas are prone to erosion and therefore where a river's course might migrate, and predict how a contaminant, such as leaking oil, will spread.

Furthermore, surficial geology provides a fairly good clue as to what soil type might be found in an area. Soils are important factors in determining the plant life that could grow, which in turn regulates what animals might reside there. Knowing this information can save a lot of time and resources instead of randomly digging wells in search of water or roving about aimlessly looking for a plant.

Currently, I am working for the Kenai Watershed Forum and the Kenai National Wildlife Refuge to create a digital map of the surficial geology of the western Kenai Peninsula.

I digitize the geological deposits delineated by Dr. Dick Reger, a local geologist with a wealth of knowledge, who interprets a combination of color-infrared aerial photos and airborne LiDAR. This useful product will not only enable both organizations to conduct informed and efficient research, but will also help with local community planning. The completed map should be available online sometime this year.
Megan Haserodt recently graduated with a B.S. degree in Geology from Hope College in Holland, Michigan, and is now an Environmental Scientist at the Kenai Watershed Forum. Her favorite rock is the Copper Harbor Conglomerate found in northern Michigan. You can find more information about the Kenai National Wildlife Refuge at or


Sun, 05/20/2018 - 21:51

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