Ecosystem Scientist, Wapusk National Park
SPOT Image showing beach ridges ©2008 CNES, Licensed by Iunctus Geomatics Corp., www.terraengine.com
Think of beach ridges, and the imagination runs to sandy dunes interspersed with coastal lowlands – perhaps a nice place to hike and picnic in July or a place to rest after a day by the water. The beach ridges in Wapusk National Park fit this image in some ways – they are formed by wave and current action on sands, pebbles and gravel and are nice, breezy, dry places in July. But in other aspects, they are drastically different. Distance from the coastline is one thing that sets them apart. Although some of Wapusk NP’s beach ridges are immediately beside the water, older beach ridges can be up to 15-20 km from the coast. The gradual rising of the Hudson Bay Lowlands, coupled with the low elevation of the region, has left noticeable beach ridges along the eastern shore of Wapusk NP from Cape Churchill to Broad River. As the land has slowly risen, freed from the weight of glaciers following the last ice age, coastal influences such as wind, storms and waves have built ridges along the high tide line each year. Over a few years the ridges, no longer at the coastline, become landlocked. Through this process, called isostatic rebound, Wapusk NP is actually getting bigger every year! In fact, the edge of Hudson Bay, where it meets the Manitoba coast, is known as one of the more dramatic areas of isostatic rebound on earth, with the land emerging out of the Hudson Bay at a rate of 40 cm -1 m per century!
These beach ridges, currently making up one percent of the park area, are covered in the only vegetation community truly classed as dry tundra in Wapusk NP. Newly emerged, or young beach ridges are generally easy to spot on satellite images such as Google Earth, as they appear as white, wispy features almost like scratches on the surface of the land. They are irregular in shape, being formed by currents and storm events that took place in the past. Further inland, the ridges become covered in shrubs and trees and are more difficult to see from the air. Often trees, such as spruce, indicate the higher ground of the beach ridges.
On most new ridges, the vegetation consists of low-growing woody shrubs such as Mountain avens, bearberry, Lapland rosebay, and buffaloberry, interspersed with sedges, lichens and the few herbaceous plants that can withstand the dry, exposed conditions on the ridges. In winter, snow is blown off the tops of the ridges and forms drifts on the lee side causing moist pockets, which are colonized by other shrubs such as low growing willows. On the undisturbed ridges, arctic plants common in areas further north, such as alpine azalea and nard sedge, can be found.
Mountain avens growing on a beach ridge © Parks Canada
The beach ridges make good habitat for arctic and red foxes, and many dens are occupied year after year. Around fox dens, bright greens indicate grasses and sedges growing where droppings fertilize the ground. Caribou migrate to the coast in spring and travel along the ridges with their calves, foraging on the abundance of grasses and lichens through the summer. Their trails etch long white scars into the gravel and vegetation and their droppings, common along the ridge top trails, leave a pungent smell and become freeze-dried.
Stone tent rings, hunting blinds and caches found along beach ridges farther inland attest to early human use. Perhaps these spots were nice breezy places to hunt and get away from the mosquitoes which are so numerous in low lying areas. Some of these archaeological sites are now 10 km inland, with driftwood larger than the trees found along the current coastline of the park. In recent history, the military used the beach ridges as landing strips and vehicle access points, setting up observation towers along these higher landscape features. Today, one scientific research camp (Nester One) is located on a beach ridge.
The beach ridges of Wapusk NP are a testament to change along western Hudson Bay, both in human use as well as geological process, and are a valued and special part of the landscape of this national park.
A view of Nester One research camp © Parks Canada