From
Pye, E.G. 1997. Roadside Geology of Ontario: North Shore of Lake Superior; Ontario GEOservices Centre, ROCK ON Series 2, 164p
AGUASABON GORGE
“The turnoff to the Aguasabon River gorge is located just west of the Aguasabon River highway at the west end of the town of Terrace Bay. Parking and viewing areas are found at the end of the road, a few hundred metres south of the highway. A wheel-chair-accessible boardwalk has been constructed to an observation deck.
From the observation deck, you can see the water of the Aguasabon River plummet 30 metres over a narrow waterfall and make a sharp turn to flow through a deep rock gorge towards Lake Superior. In the spring, a dam located upstream along the river is opened, swelling the river and enhancing the spectacular waterfall.
The rock at the waterfall is granodiorite. An igneous rock similar to granite in appearance and composition, it is approximately 2.60 billion years old. The river has eroded its channel along regular fractures or joints in the bedrock, resulting in the sharp turn in the gorge.”
From the “Tourist Information Plaques”
1) “The surrounding bedrock called the Terrace Bay ****1**** , 25 km long and 8 km wide, was originally formed inside the earth’s crust as a huge chamber of molten rock that gradually cooled and crystallized”
2) “The igneous rock exposed at the falls is granodiorite , composed mainly of ***2a*** and **2b**. It was formed 2.5 billion years ago during the ***2c** age”
3) “Glaciers sculpted this landscape at least four times during the last Ice Age. How did this affect Aguasadon Falls? In a word – Joints. When magna deep within the earth gradually cooled and crystallized, it formed the rock ****3a****** - criss-crossed with brittle fractures called joints. These joints grew larger over millions of years due to major earth movements. More recently, as the glaciers melted, the earth’s crust began to rise and relief from the heavy pressure of ice caused further widening of the joints. (Rebound of the land is a process that’d still continuing) The combined effect of the uplift and perpetual erosion has exposed the jointed ****3b****** ***3c**** you see today. Aguasabon Falls occur at the junction of predominant joints and faults in the bedrock. The river above the falls and the gorge below, run parallel with those major fractures, creating the dramatic right angle bend in the river”
4) “Joints that form the vertical walls of the gorge are predominantly the results of stress during major earth movements. However joints that run parallel to the river above the falls and dip deeply in the north face, are probably caused by stresses present during the formation of the rock”
5) “Major joints and faults along the Aguasadon River have been interpreted by geologists from air photographs.”
6) “The crushed and sheared rock created in the fault zone of the gorge was removed long ago by advancing glaciers and melt water from receding glaciers”
7) “Volcanoes were popular here 2.5 billion years ago. How do we know? Well the exposed igneous rock in this area was formed deep inside the earth – far below those spewing volcanoes. Geologists call this bedrock, the Terrace Bay ****7a*** . Since the formation of the ****7b*** , the volcanoes and upper layers of the rock have gradually eroded away. In recent geologic time (end of the Ice Age) the bedrock was uplifted as the heavy glaciers melted. The falls and gorge you are about to visit have probably changed very little over the last 10,000 years”
NOTE: In order to log the EarthCache, please contact me by e-mail via the link to my profile at the top of the page, with the answers to the questions below.
Send me the answers to “fill in the blanks” in the above statements found on the plaques at the earthcache site:
a) Fill in the blanks from the above statements:
i) “1” ___________
ii)“2a” __________ “2b” ___________ “2c” ___________
iii)“3a” __________ “3a” ___________ “3c” ___________
iv)“7a” __________ “7b” ___________
b) What is the bedrock at the site called? How was it formed? Has there been any change in the falls and gorge over the last 10,000 years? Why?
c) How many joints and faults are found along this section of the Aguasadon River?
d) What are the exposed rocks at the falls (granodiorite) consist of? During what age was it formed? What colour are the exposed rocks?
e) What impact did the Ice Age glaciers have on this area? Why do we no longer see any crushed and sheared rock from the Ice Age glaciers at this site?
f) Estimate the depth and width of the deep rock gorge as you look downstream from the viewing area
Although not a requirement to log this earthcache – please take a picture of yourself with the falls or gorge in the background so that we can get a perspective of the water flow during the seasons.
CONGRATULATIONS TO 'ragbag' ON THE FIRST-TO-FIND