Delta delights: glacial meltwater, tides, winds, and waves conspire to mold an Alaskan coastline

Natural History, July-August, 2004 by Robert H. Mohlenbrock

Two hundred fifty miles east of Anchorage, the glacier-fed waters of the Copper River spread across a fifty-mile-wide delta before emptying into the Gulf of Alaska. The surrounding landscape is alluvial fan and low-lying wetlands, which extend inland as far as thirty-seven miles, all interleaved with glacial moraines and spurs of the Chugach Mountains to the north. Although bordered by glaciers, the delta is sheltered by the mountains and faces the warm Alaska Current, making its climate unexpectedly moderate: summers are mild, winters are cool but not cold, and al] the seasons are wet.

Largely under the management of the Chugach National Forest, the delta is a breeding ground or resting place for 6 million migratory birds, including American wigeons, dusky Canada geese, green-winged teal, mallards, northern pintails, trumpeter swans, and western sandpipers. Salmon--chinook, coho, and sockeye--run at various times from late May through September, and Dolly Varden char and cutthroat trout are plentiful in the streams. Beavers, black bears, brown bears, harbor seals, moose, sea lions, sea otters, and wolves are among the local mammals.

The main obstacle to anyone who wants to explore the delta is getting there. To reach Cordova, the nearest town, you can take a commercial flight, then rent a vehicle locally. Ferries in the Alaska Marine Highway system also haul passengers and vehicles to and from Cordova year round. My wife Beverly and I had our van, so we and van took the eleven-hour ferry ride from Seward.

The largest earthquake ever recorded in North America, rated at 9.2 on the Richter scale, was centered only 150 miles west of Cordova. It struck at 5:36 P.M. on March 27, 1964, causing i15 deaths in Alaska alone, 106 of them attributable to the ensuing tsunamis. The quake damaged the so-called Million Dollar Bridge, built across the Copper River in 1908, at the then-exorbitant cost of about $1.5 million, for the transport of copper ore by rail to Cordova. (The bridge was later converted to carry road traffic, and is now preserved largely as a curiosity.) The quake also lifted the entire Copper River delta between six and twelve feet, elevating large zones of brackish marshes above the influence of the tides.

The Copper River alluvial fan is an outwash plain, that is, formed from sediments deposited by glacial meltwater. It is made up mostly of streams, abandoned stream channels, tree- or shrub-dominated terraces, and scattered ponds. Inland, nearer the glaciers, the terrain is rougher, with more distinct terraces. Peat lands appear on the terraces wherever a growth of sphagnum moss has accumulated in shallow depressions. Closer to the sea, where the terrain is smoother, forests of Sitka spruce and western hemlock have developed. Keith Boggs, an ecologist and the manager of the Alaska Natural Heritage Program at the University of Alaska Anchorage, has defined and described those and other plant communities of the Copper River delta.

Within the marshland uplifted by the earthquake, shrubs and trees now grow on the levees that border ponds. The ponds are three to four feet deep and range in area from an acre to more than ten acres. Tidal creeks still form a branching pattern within the uplifted marshland, nearly overflowing their banks at high tide but often turning into freshwater streams when the flow is reversed at low tide. Fronting the area are sea cliffs as high as six feet, which were formed prior to the earthquake by the action of ocean waves. Between the cliffs and the sea, the rhythmic movement of the tides is forming a new tidal marsh that includes mudflats, tidal creeks, tidal marshes, and tracts of shrubs.

Mixed in among the terraces, levees, and ponds are long, narrow dunes formed by onshore winds funneled upriver. They range between twenty and 250 feet high and run as long as nine miles. Although they are wider and steeper upwind, vegetation grows on all sides; the tops, however, are usually bare sand.

The wind as well as the ocean currents and waves also create beaches and back dunes at the edge of the mainland. The same forces have formed small barrier islands and spits of sand offshore, which help shelter the mainland. The beaches are ideal for beach combing, clamming, and observing brown bears and other wildlife.

The forty-eight-mile-long Copper River Highway, which extends east of Cordova and ends at the Million Dollar Bridge, provides an easy route across the delta. The first section, a twelve-mile stretch, is paved; the rest is gravel. Along the way, visitors have access in the Chugach National Forest to various campgrounds, cabins, observation platforms, and boardwalks. In addition, several side roads and trails lead to close-up views of glaciers and other attractions. One side road, on the approach to Million Dollar Bridge, ends at an observation platform overlooking Childs Glacier. The glacier frequently calves huge chunks of ice into the Copper River.

HABITATS

Outwash plain On alluvial soil, Sitka spruce is the dominant tree, and the ground is usually carpeted with mosses. Shrubs include Alaska blueberry, devil's club, and salmonberry. Oak fern and spinulose wood fern are common, along with strawberryleaf raspberry, threeleaf foamflower, and twisted-stalk. Where conditions are somewhat wetter, marsh horsetail is common beneath a dense growth of Sitka alder, lf the soil is sometimes inundated by river water, either black cottonwood dominates above a shrub layer of Sitka alder, or shrub-size Sitka alder simply grows along with a fairly continuous ground cover of bluejoint (a grass). In ponds, Sitka sedge often forms dense stands; other common species are bluejoint, buckbean, marsh five-finger, and marsh horsetail.