The Greenbough Esker

The Greenbough Esker is a prominent landscape feature of the upper Ottawa Valley that runs from south of Deux-Rivières to the vicinity of Wendigo Lake, roughly paralleling the Brent Road. The peatlands at its southern end support unique vegetation types and some uncommon to rare plant species. While the northern portion of the esker has been disturbed, the southern portion is largely undisturbed and has been recommended for protection as a Conservation Reserve.
disturbed section of Greenbough Esker

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A disturbed portion of the Greenbough Esker just north of Deermeadow Road. Eskers are a convenient source of sand and gravel.

An esker is a (usually) steep-sided ridge of sand / gravel that is the relic streambed of a meltwater river that flowed on or beneath a glacier. That is, the ridge is composed of the sediment deposited by the river. The steep sides are due to the sediments collapsing when the enclosing ice melts away. They are often tens of meters high and may extend for many -- in some exceptional examples, hundreds -- of kilometers. Eskers generally "flow" in the same direction as the glacier flows.

undisturbed section of Greenbough Esker

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The side slope of an apparently undisturbed portion of the Greenbough Esker just south of Deermeadow Road. A dry redpine forest grows along the ridge. We found it very difficult to effectively photograph the undisturbed esker within the bush. It is sad that the esker can best be seen where it is most disturbed.

The Greenbough Esker is traceable from just south of Deux-Rivières and runs southwards, roughly paralleling the Brent Road. It lies between the road and Greenbough Lake, is breached by Corice Creek (Alder Creek), crosses [and then recrosses ?] the Brent Road and disappears in the vicinity of Windigo Lake (Wendigo Lake). (The various accounts of the esker differ as to its traceable extent. It is certainly very prominent where it crosses Deermeadow Road and much less so where it crosses the Brent Road to the south.)

The Greenbough Esker crosses Deermeadow Road, just a little east of the Brent Road at military map reference 17TQM 068 178 (NAD83).

Greenbough Esker where transversed by the Brent Road

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The Greenbough Esker where it is cut by by the Brent Road.

According to Nature Guide to Ontario:

This 6 km long esker, the largest in the region, extends from Deux-Rivières to Wendigo Lake. Wooded uplands support Red and White Pines as well as Large-toothed Aspen, White Birch and White Spruce. The esker gives rise to significant wetland complexes that include kettle lakes. Rare plants such as Small Bur-reed, Virginia Chain Fern, and Swamp Beggar's-ticks grow in peatlands bordering the southern third of the esker.

Fen associated with Greenbough Esker

(photo by Bob: 2007-06-22 - explore

This little fen along the Brent Road is associated with the Greenbough Esker. The esker and its surrounding peatlands forms a landform-vegetation complex that is unique in this area.

Greenbough Esker wetland

(photo by Diana: 2007-07-10 - explore

We have posted this picture previously with the title "Northern River". In fact, it is not a river at all, but is part of the wetland complex at the southern end of the Greenbough Esker.

from the Natural Heritage Information Centre:

The huge Greenborough [Greenbough] Esker is the most conspicuous landform in the [area] and greatly affects the form and constitution of the vegetation. Beautiful intolerant upland forests of Red Pine, White Pine and some Jack Pine cover the ridge top, with Large-toothed Aspen, White Birch and White Spruce and Trembling Aspen being locally important. The undergrowth is typical of dry, drought-resistant shrub and herbaceous sandy vegetation throughout the site district. Extraordinary peatlands have developed in the postglacial kame deposits on either side of the southern [end] of the esker. Ponding and stagnant ice blocks have permitted the formation of a complex series of open graminoid fen-like peatlands, surrounded by Black Spruce - Larch forest. Some form deep kettles in esker and kame sands, while others are more open, creek-side sites, with shrub-rich areas as well. Typical bog vegetation dominates much of this areas but in several a variety of unusual peatland species with fen affinities were found ... The size and condition of the esker landform is also unmatched in either site district [5-9 and 5-10], despite the degree of disturbance to it ...

The Greenbough Esker plays an important role in establishing the glacial history of the Ottawa Valley. As the Wisconsinan Glaciation retreated to the north, the glacial great lakes found successive outlets to the sea, farther and farther to the north. Drainage eventually shifted from across Algonquin Park to down the Ottawa Valley. The opening of the drainage down the Ottawa Valley was controlled by the ice sheet blocking the valley south of Mattawa. However, it has always been a problem that no prominent drainage channels have been found in the Ottawa-Mattawa system to mark the path of the water flowing between the ice margin to the north and the highlands to the south in this portion of the Ottawa Valley. That the Greenbough Esker was not swept away by the breakthrough of the drainage into the Ottawa Valley is explained by the realization that there must have been a further ice blockages downstream of Deux-Rivières. Consequently, during this phase of the drainage, Deux-Rivières and the northern portions of the Greenbough Esker were submerged under a glacial lake. For a more detailed explanation, see J.E. Harrison (1972).

Alder Creek aka Corice Creek

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Alder Creek (as named on the Algonquin Park Canoe Routes map) is also known as Corice Creek (on the National Topographic Map Sheet -- Brent, 31L/1). In the present era, it is a very small creek. And yet it completely breaches the Greenbough Esker between Greenbough Lake and Deermeadow Road. There must be some interesting geologic history involved here. We assume that at some stage, a very large lake was impounded to the west of the esker, and it broke through here and drained to the east.

As part of the Lands For Life process, the Greenbough Esker has received some measure of protection. The portion north of Deermeadow Road has been designated a Resource Management Zone, while the southern portion has been recommended as a Conservation Reserve.

According to the Ontario Land Use Policy Atlas for the Greenbough Esker Resource Management Zone (© Queens Printer for Ontario, 2006):

The Greenbough Esker is a large and intact earth and life science feature in Site District 5E-10. The central and southern portion of this site contains an excellent example of a mature, undisturbed upland pine forest; consisting of primarily white pine, red pine and jack pine in various combinations growing on an esker landform. Peatlands have developed in places where piles of glacial deposits break up the landscape into humps and hollows and restrict the drainage. These peatlands support unique vegetation types and many uncommon to rare plant species. The Resource Management (RM) Zone accommodates a wider range of land uses and activities, with some limitations. The RM zone encompasses the prominent, northern portion of the of the esker landform between the Brent Road and Greenbough Lake, largely north of Deermeadow Road. It also includes a small area to the southwest of Deermeadow road. The linear integrity and view of the esker shall be maintained in this zone.

Resource management policies for the Greenbough Esker will ensure the long-term protection of the unique earth and life science features while providing for integrated resource management opportunities where appropriate ...

Greenbough Esker

(photo by Diana: 2007-07-10 - explore

Unfortunately eskers are usually viewed as something to be exploited, rather than conserved -- a ready source of gravel to facilitate the construction of logging roads.

This photo was taken just at the boundary of the northern and southern portions. Perhaps we are misinterpreting the situation, but it appears to us that at this location, the disturbed portion of the esker is being reconstructed, while continuing to supply gravel to the ongoing logging activities. We assume, however, that after the "excess" material has been removed, the reconstructed esker will be left to be colonized by the surrounding forest.

Greenbough Esker

(photo by Diana: 2007-07-10 - explore

This view from the top of the reconstructed part of the Greenbough Esker provides some sense of the scale of this feature.

Sources

J.E. Harrison (1972), Quaternary Geology of the North Bay -- Mattawa Region, Geological Survey of Canada, paper 71-26.

Winifred (Cairns) Wake, John Cartwright, Anne Champagne, Kathy Parker, and Martin Parker, eds. (1997), A Nature Guide to Ontario, University of Toronto Press.