This escarpment is the northern wall of the Ottawa-Bonnechere
Graben, an ancient rift valley formed by the subsidence of the
earth between two faults, the Mattawa and the Petawawa faults.
Graben is the German word for ditch. The Ottawa-Bonnechere Graben
runs from the Ottawa-Montreal area on the east to near Sudbury and
Lake Nipissing on the west with a branch called the Timiskaming
Graben.
From Wikipedia: A graben is the result of a block of land being
downthrown producing a valley with a distinct scarp on each side.
Multiple graben can form with ‘horsts’ between
them.
Graben are produced from parallel normal faults, where the
hanging wall is thrust down and the footwall is pushed up. The
faults typically dip toward the center of the graben from both
sides. The Luskville Trail climbs the northern scarp of the Ottawa
Graben, which is still very distinct and precipitous at this
location. At the top you can look south over the Ottawa Valley. At
the end of the last glaciation you would have been standing on the
shoreline looking out over an inlet of the Atlantic Ocean called
the Champlain Sea, but as the land rebounded from the tremendous
weight of the ice sheet the landscape before you was created.
The Mattawa and Petawawa faults are still active and produce
small earthquakes on a regular basis, the 1935 Timiskaming
Earthquake, a magnitude 6.2 earthquake that occurred on November 1,
1935, was the last significant earthquake.
To log this earth cache, go to the posted co-ordinates and note
your elevation at the Luskville Falls. Now climb the escarpment on
the trail to the ‘Pontiac Lookout’. You will find maps
on the information plaques at each of these locations.
1. What is your distance from the posted co-ordinates, and what
is your elevation now? Your GPS may not provide very precise
altitude readings, but do your best with what you have
available.
2. What is the predominant tree growing on the
escarpment’s slope and the predominant tree at the top?
Why?
3. Take a photo of yourself or your group at the look-out with
the Ottawa River in the background.
Log your find with the photo then email the answers to me:
Bluelamb03
The trail is steep and rocky so sturdy footwear and lots of
water is advised. If conditions are wet or icy the trail can be
hazardous so take care. The vegetation on the escarpment is fragile
so it’s important to stay on the trail. Enjoy the hike, enjoy
the view!