Hundreds of years ago the muskeg meadow next to the Auke Bay school was beachfront. Ten thousand years ago it was underwater, as was most of the Mendenhall Valley. Any area that has underlying strata of Blue Clay was once ocean floor. Gradually the land rises, the sea retreats and the tidal estuaries become drier and drier.
We are lucky to live in an area of rapid landform change. Evidence of these processes is all around, but it sometimes requires some help to see it. The Mendenhall Watershed Partnership's first autumn meeting was last week and Richard Carstensen of Discovery Southeast showed a slideshow of maps, photos and landforms that lead us to these conclusions.
Glacial retreat is a concept we all accept. The glacier that provides our city's backdrop was once much further down the valley than it is today. Like most of us, I thought that it had been like the Glacier Bay setting with the mouth of the valley hidden under a wall of ice, but the geologic evidence shows that it was much more restrained.
The Taku Boulevard Moraine marks the edge of the glacier's advance. This berm of soil, gravel and boulders was left behind as the ice sheet paused and then retreated. It was ocean up to that point, and the valley floor filled with the ocean bottom sediments until it got shallow enough for the outwash of the glacially eroded sediments to cover the blue clay with silt and gravel.
That little ridge on the left side of the glacier, the one that looks like it just barely poked out enough to see the light of day, has been found to contain fossilized deepwater clams. The ocean was deep enough there that it never went dry. Today it has the beginnings of a spruce forest and middle school students use it as a study site to follow the processes of land change. The land shapes show the story, step by step the changes leave traces and after them come the plants.
Vegetation changes, tide land becomes marsh, marsh becomes grassland and eventually some willows find a place dry enough for them to grow, then an alder thicket, then a couple of spruces. We can see the beginning of this change every day as we drive along the Wildlife Preserve and see the silvery foliage of the Hairgrass where it spreads along the highway. It is one of the most obvious transitions in our locale. In 10 years the wetter soils that were primarily populated with sedges have lifted enough for the next layer of plants to get established.
Mary Lou King told me the changes in the grass population in front of her Sunny Point home were proceeding at such a rapid pace that it was visually astounding. Very few years ago there was no grass there at all, and now it stretches a hundred feet out into the channel and a mile along the road. This is not a case of an introduced invader displacing a native species; this grass is local too.
That uplifted muskeg meadow next to the Auke Bay school is being excavated. We can see the layers in the peat, including the one where a volcano erupted and smothered the forest with a blanket of deadly ash, killing the big trees and sending the process back to the earliest succession plants. The surface of the meadow shows us a similar story, the muskeg plants are becoming fewer and the grasses are becoming more plentiful. Trees and shrubs have made inroads, too, and that ancient plant community is changing.
This excavation also allows us to have access to this valuable resource. The peat that underlies the muskeg is marvelous soil building material -- my own garden and landscape is built on a mixture of this partially decomposed vegetation and enough gravel to provide drainage. Landscape plants have responded spectacularly. Vine Maples and Japanese Maples are thriving and the feeling of recycling the resource makes it even more delightful.
It is not only the underlying strata that get recycled. We peel up the surface layers of vegetation and salvage it for use in other locations. These hundreds of years old combination of mosses, Labrador Tea, Creeping Dogwood and Dwarf Blueberry are being lifted like sod and replanted in some of the finest developed landscapes of our region. People who appreciate the centuries of growth that it took for this community to develop can have it laid in their yards and in a year it is back growing happily. It is like having a museum exhibit, a slice of the everchanging landscape.
David Lendrum is a master gardener and owner of Landscape Alaska. Any responses or questions can be sent to www.landscapealaska.com.
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