Cavernes de Pembroke

© Google

Île aux Allumettes, rivière des Outaouais, 

en amont (à l'ouest) de la péninsule dont il est question plus bas.

Les cavernes sous la rivières des Outaouais, du moins celles de la région de Pembroke, refont brièvement surface, si la chose est possible, le temps de présenter trois liens qui nous laisseront un peu moins ignorants sur la question. (Voir mon billet du 15 décembre 2012.)


1. Référence à un article de Sawatzky dans le CGRG Bibliography of Canadian Geomorphology

Résumé
«Ottawa River Caves with over 4 km of passages. The caves lies under a large peninsula* on the prov. Ontario, under several islands, and under the Ottawa River within the prov. Quebec. There are two major sinks and at least five major resurgences. The exploration and survey techniques are discussed.»

Sawatzky, D., «Canada's longest cave dive, Ottawa River Cave», Cave Diving Magazine, no 3, 1991, 18-23.

* La «large peninsula» est la pointe de terre que doit contourner l'Outaouais en aval de l'île aux Allumettes.Voir la carte plus haut.


2. Description des cavernes (pdf) par le Dr Allan Donaldson, de l'Université Carleton (Ottawa).
Publiée par l'Ottawa River Heritage Designation Project (organisme qui met en ligne des documents très intéressants, et qui œuvre pour la désignation de la rivière des Outaouais parmi le Réseau des rivières du patrimoine canadien. La version française des documents est cependant moins complète que l'anglaise).

«Caves of Wonder!
The Ottawa River’s Underwater Caves

In the township of Westmeath, just south of Allumette Island, lies an extensive series of caves that may well form Canada’s largest cave diving system. Located under a large peninsula on the Ontario side of the river, under several large islands in the centre of the river belonging to Quebec, and underthe river bed itself, this network includes over 4 kilometres of twisting passages (Sawatsky 6).

In this region, the Ottawa River is running over a bed of horizontally bedded limestone [calcaire Ordovicien] in which the caves are developing. The river generally runs in a NW/SE direction, but has, in this region, taken an “S” shaped turn to circumvent a large peninsula on the Ontario side. The peninsula is relatively flat, and about 1 to 4 metres above the normal river level. However, when the water level is high, half of the peninsula over the caves is submerged. Some of the water then flows under the peninsula along the fault lines and bedding planes in the limestones. It is this process that continues to form this complex series of caves (Sawatsky 1*) (p. 149).»

* Voici la référence à Sawatsky (décidément indispensable) dans la bibliographie du document :

• Sawatsky, David. “Ottawa River Caves”. Canadian Caver. (1990).

3. Interview de Sawatsky (l'incontournable !) dans SCUBA SCOOP, reprise du Ottawa Citizen (par Kathy Dowsett)

«The Ottawa River caves are relatively accessible by the challenging standards of Canadian caves, and clustered just downstream of Pembroke. They are the longest known underwater caves in Canada, with passages varying from one to 38 metres in width. The caves formed in the weak areas between layers of limestone, so in some places the passages are stacked on two levels like a parking garage. No vegetation grows in the winding tunnels, but the clams, crayfish and sturgeon that live in the river also occupy the caves, making the cave entrances near the surface popular fishing holes*.

[...]

When the silt on the bottom of the caves gets stirred up, a diver can only be seen by the occasional flashes of light on his equipment, making him look like a tasty minnow to the large fish trawling the area. When they dart in for what they hope will be dinner, it can be incredibly dangerous for a diver clinging to the nylon rope that will get him back to the surface. A school of pike gave Dr. Sawatzky some scary moments during one zero-visibility dive in an Ottawa River cave.

"There are some fairly aggressive fish in the Ottawa River, and they're in the caves as well. It's like being punched. Some of the larger fish hit very hard, so I got punched a few times by fish. When one hit my hand, I didn't let go" of his rope " -- I sort of expected it might be coming."»


* Ce qui nous ramène à notre «histoire de pêche» (Edgar, 1898 ; billet du 15 décembre 2012, voir le premier des «ajouts»).