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Back Roads Bill talks rocks - cracks, alvars, clints an grikes

This week Bill takes us on a deep dive into some interesting cracks in Earth’s crust and explains things like karstification and dolostone

Manitoulin Island is blessed with incredible natural beauty mainly because of the rocks. Its rocks are oddities that make it an unusual and extraordinary travel destination largely because of the geological anomalies found there.

Follow this through. It is the 172nd-largest island in the world and the 31st-largest in Canada. Known as the “Spirit Island” itself has 108 freshwater lakes, some of which have their own islands; in turn, several of these "islands within islands" have their own ponds. Lake Manitou is the largest lake in a freshwater island in the world and Treasure Island in Lake Mindemoya is the largest island in a lake on an island in a lake in the world. These facts alone give the island an atypical introduction.

It is about 130 km long and 50 km wide and its intriguing landscape resulted from the action of ancient rivers and glaciers that altered the soft bedrock. These actions are what make the island distinctive. It is an extension of the Bruce Peninsula and the Niagara Escarpment.

When compared to the granite of the Canadian Shield found in most of northern Ontario it is the white quartz and limestone rock and the alvars that make the island the exception. Five hundred million years ago, Paleozoic limestone was deposited in shallow, tropical seas at the time over top of the bumpy landscape of the Canadian Shield. Slowly the island was buried by these limestone sediments made from millions of sea shell pieces. The accumulation of the invertebrates’ hard parts after their deaths generated the sediment; all of this hardened into the limestone features.

Alvars- and Geomorphology 101

Alvars, (a Swedish word), are globally rare, naturally open habitats with either a thin covering of soil or no soil over a base of carbonate rock, such as limestone and dolostone. It is one reason why Manitoulin is unique.

The rock is easily dissolved by water in its many forms through a process of karstification or karst landforms. Most of the features on the island likely formed in the last 15,000 years following the last glaciation period.

The alvar vegetation community developed on many of the island’s bedrock barrens. It is a rare and sensitive ecosystem that is not found outside the Great Lakes basin. Juniper bushes and herbaceous plants such as grasses and sedges are typical of the alvar plant community.

This delicate ecosystem manages to eke out a living under extreme and fluctuating conditions of temperature, moisture and poor soils. These rare habitats still exist where flat areas of shallow limestone bedrock have been left undisturbed. More importantly, however, we now know that these openings are far from barren, for they are home to myriad distinctive plants and animals.

When you visit you will see a great deal of almost flat-lying, smooth pavement, linked to the movements of the glaciers. Soils are thin or almost non-existent. Because of the softness, the pavement's cracks form and become increasingly dissected. The fractures create blocks of various sizes called “clints.” The spaces between them are called “grikes.” These collect soil and plants take root. The sparsely vegetated bedrock barrens that develop are in fact, the alvars.

Alvars comprise a small percentage of the Earth's ecosystems by land extent. Although some 120 exist in the Great Lakes region, in total there are only about 43 sq mi (110 km2) left across the entire Great Lakes basin and many of these have been degraded by agriculture and other human uses. More than half of all remaining alvars occur in Ontario

I contacted one of the three authors of Manitoulin Rocks! Peter Russell is the retired Curator of the Earth Sciences Museum at the University of Waterloo, he is a groundwater specialist.

In 2012 he received the Lieutenant Governor’s Ontario Heritage Award for Lifetime Achievement. In the middle of the campus stands the Peter Russell Rock Garden which contains more than 80 large rocks from all over the world.

The book’s aim was to present a “simplified account” of the geological history of the area and to present interesting and unusual facts.

“The grikes average about 13 cm or so across," Russell said. "As the fractures widen through dissolution the groundwater flows to the water table. The importance of recognizing such passageways in bedrock cannot be overstated, because they have a bearing on locating landfills, sewage treatment and management of livestock manure.”

Walkerton – Ground Water

He explained the tragic events at Walkerton, situated on the Bruce Peninsula.

“In May 2000, water moving quickly through the fractured bedrock combined with subsequent lack of chlorination caused an outbreak of E.coli (Escherichia coli) bacteria in the town’s water supply,” said Russell

The result was more than 2,300 cases of gastrointestinal disease and eventually seven deaths. It was attributed to farm runoff into an adjacent well that had been known for years to be vulnerable to contamination and to two employees of the Walkerton Public Utilities Commission who could have admitted (but they falsified reports) to the contaminated water sooner.

Go for a visit

The question to Mr. Russell was, “Is there a location that represents both the alvar community and the karst process?”  

“There is some beautifully exposed pavement on both sides of the road with excellent development of clint and grike karst,” said Mr. Russell. “It is one of my favourite places to visit, especially in October when the maple trees turn red and yellow. The trees are short bonsai-like due to the lack of soil.”

This location is found at N45° 43’ 38.8” W82° 14’ 43.4” or WGS 84 17 T E403094 N5064519.

Although there are many locations to see alvars this one is found north of Providence Bay off of Highway 551 (SW corner of Mindemoya Lake). Highways 551 and 542 merge in Mindemoya, the village. Turn north onto Monument Rd. (west of Mindemoya) and drive north, 1.5 km. This is a quiet country back road, good for parking. It is a wonderful site to see the fractures and a multitude of sensitive ferns, stunted junipers and exposed dolostone pavement with no topsoil.

Junipers are like bonsai Christmas trees, they’re odd too. On Manitoulin, they are mostly low-spreading shrubs with long, trailing branches but they can grow into columns. They are evergreen with needle-like and/or scale-like leaves. The needle leaves of junipers are hard and sharp, making the juvenile foliage very prickly to handle. In some juniper species, their "berries" are red-brown or orange, but in most, they are blue; they are often aromatic and can be used as a spice and are famously known as the flavouring in gin. In fact, juniper berries are not real berries. They're cones with scales so miniature and packed down that you can't even see the scales — instead, they appear as round berries. Only the female tree makes the berries, while the male just has little brown cones.

There is so much to see on Manitoulin Island including finding trace fossils at Gore Bay and the Cup and Saucer Trail, close to Little Current.

The 123-page, comprehensive guide, with coloured photos, is one of the best of its kind as a stop-to-stop field guide of the island, with GPS coordinates and good directions. The first half of the book treats a broad range of topics and concepts required to appreciate the geology of Manitoulin Island, using local examples wherever possible. The second half of the book is a detailed field guide to 50 field stops on and north of Manitoulin Island to examine rocks and landforms.

A tip of the hat to the authors, I would give it a “camp badge,” this is how information for visitors should be presented as far as reaching locations with good directions. It's one of the best guidebooks in northern Ontario. You can order it through the Geological Association of Canada or elsewhere.

Most alvars occur either in northern Europe or around the Great Lakes. They do look lie stressed habitat that supports a community of rare plants and animals, including lichen and mosses are common species. Trees and bushes are absent or severely stunted. I have seen the alvars in the Burren region (County Clare) of Ireland; at the time I could have closed my eyes and imagined Manitoulin. More on the alvars here.

Take the swing bridge

The Little Current Swing Bridge is interesting. At Little Current this summer it is your gateway to exploring. Most people know a crack when they see one, but that doesn't mean they understand or have thought much about cracks like the clints and grikes of Manitoulin Island. Understanding the Walkerton tragedy through visiting the Manitoulin alvars may prove to be more than just interesting on the back roads.


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Bill Steer

About the Author: Bill Steer

Back Roads Bill Steer is an avid outdoorsman and is founder of the Canadian Ecology Centre
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