Arctic Storm Effects
We have been taught that dramatic changes to the earth's surface can be created by almost imperceptible processes acting for very long times; e.g., a tiny stream flowing for millions of years can carve out a large valley. This concept is so embodied in our thinking that it is easy to forget that many geologic processes act in an altogether observable, though intermittent, fashion.
Mount St. Helens is a particularly good example. The mountain is a thousand-year accumulation of ash falls, lava flows and pyroclastic (hot avalanche) flows. Each fall or flow is a perceptible event if someone is there watching, but each forms only a tiny, perhaps almost insignificant part of the whole mountain. And of course, much of the top of the mountain slid or blew away in just a few minutes on May 18, 1980.
Less dramatic but similarly intermittent are the geologic processes that utilize wind and water to erode away or build up coastlines. These days, because of petroleum development, much attention is being paid to the coastline along the Beaufort Sea where it fronts against northern Alaska and Yukon Territory. Scientists are finding that the barrier islands lying along this coastline undergo substantial changes in size and shape in just a matter of a few decades. However, the changes are essentially all due to storms rather than being the result of steady processes.
The most severe storms in the area generally occur in September or October. They involve strong westerly winds blowing over a fetch of open water since, during these months, the pack ice usually is many miles offshore. These strong westerly winds drive seawater onshore to cause flooding of the coastal lowlands and erosion of bluffs facing the sea. The erosion is partly due to the battering of storm waves against the bluffs and partly due to melting of ice layers contained in the bluffs. Undercut by the wave action, the bluff fronts topple down on the beach to be ground up and carried away by the water.
The waves whipped up by the strong storm winds also are particularly effective in cutting up beach materials already deposited and in carrying off the material eroded. Huge amounts of soil material are held in suspension by the violent churning motions in the nearshore waters during storms. Storm waves breaking over vessels anchored in shallow waters have been known to coat the vessels with layers of mud.
When a storm subsides, the water grows quieter and begins to lose its sediment load. Low-lying barrier islands, perhaps awash and partly eaten away by the violence, then reappear with changed shape and location.
One would think that the islands would tend to be moved eastward since the storm winds blow from the west and it is on the western side of shore features that the greatest erosion occurs. However, the islands usually migrate westward. Evidently the reason for the westward migration is that, except during the peak violence of the storm, the normal current in the nearshore region is to the west. Thus the barrier islands slowly step their way westward along the coast, each step taking place during a fall storm and in the days that follow. Some years the steps are only a few feet or are nonexistent; in others, the steps are giant strides, as much as a hundred feet.
