The Canadian La Societe canadienne Geotechnical Society de Geotechnique

River Raft Trip September 21, 2008 Field trip stops and points of interest along North River

W

S N Whitemud

Terwillegar Park 1 M E

Ft. 2 3 N Saskatchewan R

7 4 HP L 6 Whitemud Drive Whitemud 5

8 Jasper Av

82 Av HLB

JMB 9

Landing

5km

Modified from image prepared by Geological Survey. Compiled from Alberta 2001 natural colour mosaic and Alberta 2002 IRS Mosaic provided by (Photosat.ca). Alberta STRM purchased from US Geological Survey EROS Data Centre L- Lunch stop; M - muster/assembly area; HP - ; HLB - High Level Bridge; JMB - James Macdonald Bridge; - Exit 1. Field trip stops and points of interest along

M. Rally and muster point at Terwillegar Park Parking Lot Geological setting, discussion of what we will see on trip, logistics, lunch and rest stops River Safety and Donning of clothing and and River Put In.

Stop 1. Outcrops of Horseshoe Canyon bedrock units with valley incision, preglacial sand, glacial sediments - till and lake sediments

Stop 2. Whitemud Road landslide and mechanisms for failure.

Stop 3. Groundwater discharge from the buried New Sarepta Valley; Pass by ; pass by Jewish Culture Centre (Former Hillcrest Country Club)

Stop 4. Laurier Park Lunch Stop; gold panning demonstration.

Stop 5. Keillor Road instability and slope failure.

Stop 6. Hawrelak Park - reclaimed former gravel pits

Stop 7. Slope instability along Summit Drive and landscape armouring

Stop 8. Mazama Ash at High Level Bridge; sequential terrace development recorded in 4 terraces; Pollard Brick Yards.

Stop 9. Put out at Rafters Landing; Grierson Hill instability, rip-rap along bank, reclaimed landfill of Connor Hill ski club and Muttart Gardens; coal mines and Edmonton Convention Centre.

2.

The ancestral North Saskatchewan River has been flowing across the for millions of years within a broad, shallow-sloped valley, named the Beverly Valley. Parts of that ancestral valley underlie the central part of Edmonton, the deepest parts beneath the municipal airport and the Northern Alberta Institute of Technology (N.A.I.T.)

About 27,000 years ago, a major glacier from the Canadian Shield advanced over the Edmonton region and it, along with Glacial Lake Edmonton, deposited thick sediment, completely burying the Beverly Valley and masking any present-day surface expression.

The part of the river valley that is presently exposed in the City of Edmonton is only about 12,000 years old, which is relatively recent in geologic time. It was formed by the re-establishment of the regional drainage following the retreat and melting of the glaciers, but this time along a different path than the Beverly Valley.

Over the last 12,000 years or so, the river has carved down through soft sediments deposited by the glaciers, and into the harder Cretaceous sedimentary rocks, forming a series of relict terraces, separated by relatively steep erosional walls.

Stop 1. A record of time at Terwillegar Park

More than 60 million years of time are exposed in the geological record along the banks of the North Saskatchewan River at Terwillegar Park, spanning the Age of the Dinosaurs to the arrival of man in the oldest units are at the bottom of the outcrops, and the youngest are at the top (figure 1). All of the major rock units that one is likely to encounter in the Edmonton area are visible in the Terwillegar

The oldest rock unit exposed at Terwillegar is called the Horseshoe Canyon Fm. which is an assem- blage of sandy and muddy sediments deposited by rivers flowing into an inland sea during the Creta- ceous Period (~100 ma). These are the light grey rocks shown in figure 2. Lush vegetation growing in quiet backwaters along these rivers were later buried by mud, eventually turning into coal. Episodic outbursts from active volcanoes to the west, deposited thin layers of ash on the river sediments. These ash layers later transformed into clays through weathering processes and are referred to as bentonites or bentonitic clays (figure 3). The ash layer marking the time of the asteroid impact that ended the dinosaurs has been eroded away in the Edmonton area.

As the young grew, the inland seas drained and the exposed sediment was eroded by ancient river systems that flowed north and eastward. During the next 45 ma (Tertiary Period), as much as 3 km of sediment were eroded by these rivers. As these paleo (ancient) river channels migrated across the landscape, they carved new valleys and transported sand and gravel derived from rocks in the emerging Rocky Mountains. These deposits are named the Empress Forma- tion and consist mainly of quartzite, the only rock hard enough to survive the long journey by river onto the plains.

3.

Stop 1 ( ). A record of time at Terwillegar Park

Two of these ancient (paleo) river valleys are present in the Terwillegar Park area: the Stony Valley, which is exposed in the park, and the New Sarepta Valley, which is exposed downstream of the park (figures 4 and 5). The sand and gravel deposits that rest on the floor of the bedrock channel are saturated with groundwater, and are able to supply drinkable water to

In the last 2 million years a number of major continental glaciers advanced from the northeast and covered most of Alberta. At Terwillegar there is a record of only the latest glaciation which occurred about 27,000 years ago. Ice in these glaciers was as much as 1.5 km thick in places to sink many metres.

The sediment deposited by the glaciers is called till, which is composed of a mixture of clay, silt, sand, gravel and boulders. Because these sediments were subjected to the weight of more than 1 km of ice in the Edmonton area, they are quite dense and stiff, and form vertical columnar faces on river outcrops, as shown in figure 6a.

Almost all of the large boulders we see today along the banks of the North Saskatchewan River are eroded from glacial till and most are derived from igneous and metamorphic rocks (granite, gneiss) located in the Canadian Shield northeast of Edmonton. They are referred to as erratics because their original source is quite distant from where they are found today.

About 12,000 years ago the great ice sheet began to melt and the position of the glacier margin retreated northward. The eastward drainage of large volumes of glacial meltwater, combined with drainage from the mountains to the west, was impeded by the glacier mass, causing large glacial lakes to form along the ice margin. One of the largest was Glacial Lake Edmonton, the record of which is preserved in the form of layers of interbedded light colored silt and darker colored clay which were deposited on the surface of the underlying glacial till (figure 6b.) Glacial Lake Edmonton sediments cover most of the Edmonton area, accounting for heavy soils in our gardens. In places rivers flowing along the base of the glacier spilled their contents of sand and gravel within channels carved into the glacier ice. After the ice walls melted, mounds of coarser river sediments, called kames, were left along the lake margin. One such kame deposit is located directly east of Terwillegar Park in the area known as Whitemud Road.

Glacial Lake Edmonton eventually drained via a major spillway as it overfilled its shallow basin, and as the restraining ice mass collapsed during melt. In the first few thousand years after the retreat of the continental glaciers the ground surface began to rebound upwards in response to the removal of the weight of the glacier ice. Eastward-flowing rivers became re-established, adjusting to new gradients and changes to the postglacial landscape. In places the North Saskatchewan River reoccupied its former preglacial valley, but elsewhere it charted its own path establishing a new drainage route.

In last 12,000 years or so in the Edmonton area, the river has eroded down through the soft sediments deposited by the glaciers, and into the harder Cretaceous rocks, forming a series of terraces, separated by relatively steep erosional walls. Erosion continues today, but at a much slower rate than following the glacier retreat. Continuing adjustment of the landscape in response to the slow but steady erosion is demonstrated by the numerous landslides along the river banks. 4. Stop 1, figure 1. A cartoon of the rock record in the Edmonton Area

12 ka - Today

12.5 ka - 12 ka

27 ka - 12.5 ka

~2 ma - 28 ka

Erosion 65 ma - 2 ma

~100-65 ma (modified from R. Mussieux Geological Wonders of Alberta, Provinical Museum of Alberta)

Stop 1, figure 2. Exposed bedrock of the Horseshoe Canyon Formation

Glacial sediments ~30,000 to 12,000 years B.P.

Horseshoe Canyon Fm. >65 million years B.P. (bedrock)

River floodplain sediments 12,000 years B.P. to Pesent

(photo M. Fenton, 2000) 5. Stop 1, figure 3. Bentonite - A Slippery Little Devil

(modified from R. Mussieux Geological Wonders of Alberta, Provinical Museum of Alberta, p. 207)

Who would have thought that thin layers of weathered volcanic ash could cause so much grief in the Edmonton area?

clay formed by the weathering of volcanic ash into a mineral called montmorillonite, a member of the smectite family of clays that are known for one property -

failure in the Cretaceous bedrock units in the Edmonton area, particularly after heavy rainfalls when the clays become saturated.

make bentonite ideal for protective linings in landfills and waste pits, and for sealing pipes in the ground such as protecting water-wells from (photo L. Andriashek, 2000) surface contamination. 6.

Stop 1, figure 4: Location of ancient river valleys in the Terwillegar Park area

Big Bend Section

Whitemud Road Landslide

Stop 1, figure 5: Erosion of the bedrock surface by preglacial rivers

(photo by M. Fenton, 2000) 7. Stop 1, figure 6a: Exposure of glacial till and Glacial Edmonton silt and clay

(photo M. Fenton, 2000)

Stop 1, figure 6b: Exposure of beds of Glacial Edmonton silt and clay

(photo M. Fenton, 2000)

8. Stop 2. Real estate on the go - Whitemud Road Landslide

Much of the recently developed area in southwest Edmonton (Riverbend/Terwillegar) is located on a glacially deposited mound of sand called the Bulat Kame. The base of this sandy material was deposited in a channel that formed beneath the glacier and which is now exposed in the river valley in the vicinity of Whitemud Road. At this location the surface material is a clay cap deposited by Glacial Lake Edmonton which rests on glacial sand, that in turn rests on till and bedrock of the Horseshoe Canyon Formation.

In October 1999, a portion of the riverbank at Whitemud Road failed, carrying with it one residence and undermining two others (figures 1 and 2). A detailed study highlighted the surface of rupture within a weak bentonite layer in the bedrock (figure 3).

The timing of the slide was likely due to increased development in the Riverbend/Terwillegar area. After the clay cap was removed during construction, more water infiltrated into the sands as people began to water their lawns. Another contributing factor was that the five-year period preceding the failure had a higher than average annual rainfall which added more water mass to the soil.

All these factors contributed the slope failure, but probably the most significant and obvious one is that the homes were located on a very sharp bend (meander) where the erosive forces of the river are greatest - gravity has its day!

Numerous groundwater discharge sites are evident along this section of the river, and there contin- ues to be visible evidence of active slope instability, in some cases impacting on residences. Near- horizontal drains have been used to attempt to stabilize the banks at two locations along this stretch of the river. Stop 2, figure 1. Whitemud Road Landslide October 1999

(photo from the Edmonton Journal, Oct. 1999) 9. Stop 2, figure 2. Ruptured house foundations, Whitemud Road Landslide

(photo L. Andriashek)

Five houses were directly impacted by the landslide. The collapse of two of these homes down the river bank was captured in real time on film. Other homes along the bank are still at risk of collapse.

10. Stop 2, figure 3. Anatomy of the Whitemud Road Landslide

Sheared homes

(Source: Cruden, D.M., Martin, C.D. and K. Soe Moe, 2003. Stages in the translational sliding of 2 inclined blocks: observations from Edmonton. Proceedings of the 56th Canadian Geotechnical Conference, Winnipeg, MB.)

Slope failures in soft soils commonly occur in one of two ways; as rotational slumps, or laterally along a discrete plane of weakness, known as a translational slide. The Whitemud Road slope failure is an example of a translational slide, and took place something like this:

Rainfall and seepage from irrigated lawns saturate the soil and add water mass to the slope.

Water penetrates the ground along fractures and travels down through permeable sand of the Bulat Kame deposit.

Water percolates down through the sand and till along fractures that develop parallel to slope, and saturate the bedrock, including the bentonitic clays.

The clays swell and lose their internal strength, and all of the rock and soil mass above starts to slide horizontally toward the river.

Large cracks and fissures develop as the block of material slides to the river, and secondary failures occur in the form of semi-vertical faults called grabens.

Houses that have the misfortune to be located along one of these graben fault lines are sheared in half and topple into hole created by the slumping fault block.

Continued river erosion of the slide deposits along the sharp bend of the meander will progressively eat away the toe of the slide, causing it to steepen, slump and fail even more over time. 11. Stop 3. The Dark side of Groundwater

Groundwater, while a valuable resource when you need water, can also be a hazard, particularly when there is too much of it in the wrong place. Directly north of the Whitemud Road Landslide area is another potential landslide problem that is related to groundwater discharge from a channel aquifer in the buried New Sarepta bedrock valley. Water is an incompressible substance, and so when the weight of the overyling material increases, it transmits that pressure to the pores between surrounding soil particles, effectively buoying them and reducing the grain-to-grain friction. This increased pore- water pressure and resulting reduced shear strength of the sediment is the major mechanism for slope failure after heavy rainfalls.

Groundwater remains at a relatively constant temperature year round, about 5-70 C in the Edmonton area and so it flows out of the river outcrop year round. In winter this discharge accumulates as ice, referred to as aufeis, along the bank of the river, growing steadily until spring melt. The ice is visible long after the surface snow melts because of its greater thickness. During the summer months the discharge may not be visible as the discharging water can evaporate as quickly as it exits the ground, or as plants consume it during growth. Never-the-less, groundwater emerges year-round along the banks.

Attempts are currently underway to relieve the pressure and increase the amount of groundwater discharge by installing horizontal drains, to take the water away from the toe of the slope.

Stop 3, figure 1. Frozen groundwater discharge from the buried New Sarepta Valley

View to the north from Whitemud Rd. Landslide

Aufeis - frozen groundwater discharge

( April 2006, L. Andriashek) 12. Stop 4. Gold Mining in the Edmonton Area

Mining of placer gold and platinum in the Edmonton area preceded the discovery of gold in the Klondike by more than 40 years, and continues today with small, hobby operations.

Placer gold was first discovered in the North Saskatchewan River valley in the 1850s by Cariboo area via Edmonton.

In 1867, 175 prospectors, known as the left Eastern passing through Edmonton on their way to the Cariboo gold fields. About a third stayed in Edmonton to try their luck in

Clover, whose name survived as the districts of Clover Bar and Cloverdale.

On a good day in low-water stages, miners claimed they could recover 0.5 ounces a day, all of it as fine flakes, called flour gold associated with fine, black sand - there are no nuggets in the North Saskatchewan River. The black, heavy-mineral-bearing sand was panned to concentrate the gold, and then the gold was dissolved with mercury to concentrate it further.

Gold mining in the Edmonton area peaked between 1895 and 1907, with some 300 miners working the bars 100 km upstream and downstream of Edmonton. Larger steam-powered dredges enabled miners to extract up to 2 oz. of gold per day. In the last two years of operation about 7500 troy oz. of gold were extracted, but profits were marginal and miners left to join the 1898 Klondike Gold Rush.

Gold mining continues today as part of the sand and gravel mining operations at Villeneuve northwest of Edmonton.

Sir Wilfred Laurier Park and its link to Gold Mining in the Edmonton Area

in the area in the hopes of finding gold in the silt banks along the North Saskatchewan River.

intent was to build a powerplant, but in 1910 City Council designated it as parkland and named it Laurier Park after a visit to Edmonton by Sir Wilfred Laurier.

Parts of the area were mined for gravel and later used as a waste disposal site, but in the early 1960s the area became home to the Storyland Valley Zoo. In the late 1980s the City suggested the name be amended to Sir Wilfred Laurier Park.

13. thar river!

Stop 4, figure 1. Mining placer gold in central Edmonton using a portable grizzly (1895)

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society)

Stop 4, figure 2. A hand-operated dipper-type dredge. Gravel is load- ed onto a wheeled car which is winched to the top of the dredge and dumped into the sluice box (1894)

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society)

Stop 4, figure 3. A conveyor-type bucket wheel dredge. Gravel is carried by buckets to the top of the dredge where it was washed in a revolving drum called a trommel. Coarse gravel passes through the trommel and fine-grained materials, including gold, pass through holes in the trommel into a sluice box.

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society) 14. Stop 5. Piling on Keillor Road

In its heyday Keillor Road was arguably one of the most scenic drives in Edmonton, with the road hugging the south riverbank near the Whitemud Equine Centre. However, it was doomed almost from the time it was constructed, requiring constant maintenance to repair cracks in the road. Slope instability was identified along Keillor Road in 1994, and the road was closed to vehicular traffic and converted to a pedestrian and bicycle corridor. In 1996 a significant slide occurred and a year later a concrete retaining structure was installed to stabilize the roadway. In 2001 cracks started to develop in the road way behind the wall, and slope movements began to accelerate, leading to a significant collapse in spring of 2003. While initial investigations in 1995 indicated that the slope failure was likely shallow and in the glacial sediments in the upper slope, more detailed studies after the 2003 slide indicated that the slide was seated much deeper, likely in a bentonite seam in the Horseshoe Canyon bedrock, a few metres above the river. There are numerous active movements visible in the lower portion of the slope in this stretch of the river, between the Equine Centre and Hawrelak Park, as evidenced by the lower portions of the slope which consist of landslide debris (colluvium) that continues to be eroded away by the river.

Stop 5, figure 1 Keillor Road Slope Failure, 2004 View to southeast

(photo M. Fenton, 2004) 15. Stop 5, figure 2. Keillor Road Slope Failure, 2004

(photo M. Fenton, 2004) View to the north along the east bank of the North Saskatchewan River

16. Stop 6. Sand and gravel in Edmonton - The Pits

Sand and gravel are used primarily in making asphalt for roads, and concrete for foundations, and when one considers how much we consume, its easy to see how valuable sand and grav-

Consumption of sand and gravel was estimated 10 years ago to be about 300 million tonnes, and that number is probably considerably higher now. The composition of the rocks that make up the deposits determines how the material can be used in construction. For example, gravel that is used to make concrete, which must with- stand very heavy loads in foundations, must be made of rocks that have great strength, such as quartzites. Only certain deposits, such as those in preglacial river channels, are suitable for concrete aggregate. Gravel used for asphalt, on the other hand, does not need to be as strong, and softer rocks such as sandstone, can be suitable. These are the rock types that are typically found in gravel bars or river terraces along the North Saskatchewan River. As the City developed over the past 100 years, local deposits of sand and gravel were con- sumed first, then more distant sources were mined. Most local sources were found on flood- plains inside meanders of the river. Every major meander in Edmonton provided a source of sand and gravel from the buried preglacial Onoway Valley near Villeneuve, about 50 km north- west. The following four figures are aerial photographs taken of the area now know as Hawrelak Park. They show the sequential development of the floodplain meander from a golf course to a gravel operation to lastly, a reclaimed recreational park.

Stop 7. Prior to 2002 a large blue structure was erected on the west river bank which was highly visi- ble from many areas of the city, especially travelling north toward Groat Bridge. This structure was a protective barrier to minimize erosion and infiltration of water into the slope. Between 2001-2002 studies studies for the construction of a residence at this location assessed the subsurface geology and groundwater and their impact on slope stability. Studies confirmed the site is situated above the confluence of the buried Stony Valley and the larger Beverly Valley, the ancestral valley of the North Saskatchewan River. More than 40 metres of Glacial Lake Edmonton clay, till, and preglacial sand and gravel underlie the site, with groundwater seeping out of the lower slope just above the river. A weak bentonite zone was encountered in the bedrock below the channel floor, and was a concern with respect to slope instability. Horizontal drains were installed to allow for easy drainage of groundwater from the channel sand and gravel, thereby reducing water pressure which could lead to a large slope failure.

17. Stop 6. Evolution of a gravel pit - Hawrelak Park

Mayfair golf course area 1924 Mayfair golf course area 1952 - Note river scroll bars and absence of: Note gravel pit south of golf course gravel pit south of the golf course, Groat and new housing developments Bridge and Provincial Museum

Mayfair golf course area 1962 Mayfair golf course area 1988 Note enlargement of gravel pit and The gravel pit has been reclaimed and construction of Groat Bridge developed as Hawrelak Municipal Park (all photos modified from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society) 18. Stop 8a. Just how old is the North Saskatchewan River?

Terrace 4

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society)

Four major terrace levels are recognized along the banks of the North Saskatchewan River, with the oldest, and uppermost, dating back to about 11,000 years ago. Most of the river valley was eroded in the first 2500 years following the retreat of the last glacier, with only minor incision occurring in the last 8500 years. The Alberta Legislative Building is situated on the uppermost terrace.

While the river may seem tame and gentle, with perhaps a few mood swings during spring ice-break up, at times the river can get downright ugly especially when heavy rains can cause the river to rise as much as 10 metres higher than present level. These are often referred

The last notable flood event occurred in the late 1980s, but it paled in comparison to the 1915 flood which caused enormous damage. Major structures such as the Low Level Bridge were in danger of being destroyed and innovative methods were adopted to protect them, as the following figures show.

19. Stop 8a. June 1915 flood. View east from High Level Bridge. Submerged flood plain

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society)

Stop 8a. Low Level Bridge stabilized by train unit during the 1915 flood.

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society) 20. Stop 8b. When mountains blow their tops- Mount Mazama Volcanic Ash

Mt. Mazama Volcanic Ash

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society) ALBERTA

Edmonton N

Calgary U.S.A. Mt. Mazama Ash Layer 1450 km

Extent of ash deposit Crater Lake

(from R. Mussieux Provinical Museum of Alberta) 6800 years ago Mount Mazama, located 1450 km to the south in Oregon, erupted explosively.

The explosion was almost 100s greater than Mt. km3 of the mountain blew away, and the ash plume covered almost 1.3 million km2, travelling as far north as Lac LaBiche 200 km northeast of Edmonton.

The eruption drained the magma chamber causing the mountain to collapse inward. This created a 1200 m deep and 9 km wide caldera, which is presently occupied by Crater Lake.

In Edmonton the ash can be found as a 1 cm thick layer preserved along the lowermost terrace of the river. The ash is silty pinkish white and is gritty because of the high volcanic glass content. 21. Stop 9. King Coal - Fuelling growth in the Edmonton Area

It was the abundance of coal that enabled Edmonton to become established as a city so quickly. Coal mines operated for nearly a century, with the last mine at Whitemud Creek closing in about 1970. More than 100 mines operated in the area, with most being ephemeral, produc- ing mainly in winter along exposures along river cliffs. Well-known river-cliff sites include: east of Edmonton Convention Centre and Grierson Hill, cliffs beneath Scona Hill on 99th street, above Riverdale and Alex Taylor Road, in the cliff east across Rundle Park, and in the ravine north of the Strathearn District. Most of the small mines peaked by 1900 and died, leaving 17 large, well-planned mines to operate for the next 70 years (figures 1 to 3). Coal seams in the Edmonton area can be up to 3 m thick and extend for many kilometres. In which burns for a long time with a bright flame and produces low amounts of ash.

More than 13 million tonnes of coal were mined, with most coming from the Clover Bar Seam. Mining was done almost entirely underground and hauled to surface along inclined slopes or vertical shafts. Most seams were about 1 to 1.5 m thick, so miners had to dig on their knees (figures 4 to 6). The room-and-pillar system of mining was used in which coal was extracted from a rectan- gular area (the room) leaving coal all around (the pillar) to take the weight of the rocks above. The miners then evacuated, hopefully before the pillars failed and roof crashed down. There

The development of natural gas supplies in Alberta spelled the end of coal as a fuel source fired electrical generation facilities. Old mines were abandoned and most successfully reclaimed (figures 7 to 10). Stop 9, figure 1. Principal coal seams and depths of major coal mines

22. (from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society) Stop 9, figure 2. Coal Mines in the Edmonton Area

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society)

Major Coal Mines 1 Beverly Dawson 2 Black Diamond Mine 3 Old Bush 4 New Bush 5 Clover Bar 6 Dawson 7 Fraser-McKay 8 New Humberstone 9 Kent 10 Marcus Twin 11 New Ottewell City 12 Penn, Chinook Mine 13 Premier 14 Red Hot 15 Standard 16 Twin City 17 Whitemud Creek 18 Strathcona

Boundary of underground coal mine 23. Stop 9, figure 4. Present-day exposure of coal seam along the south bank of the North Saskatchewan River near Lavigne Landing)

(photo W. Langenberg, AGS)

Stop 9, figure 5. Underground exposure of hand-dug coal seam, circa 1907.

(from Edmonton, The Life of a City edit.. B. Kesketh and F. Swyripa, 1995)

Stop 9, figure 6. Exiting coal mine with hand-pushed coal carts, Nov.6, 1891

(from Edmonton, The Life of a City edit.. B. Kesketh and F. Swyripa, 1995) 24. Stop 9, figure 7. Strathcona Coal Company Mine Stop 9, figure 8. Loading coal onto barges, James Stewart Mine Company

(both photos from Edmonton, The Life of a City. Edit.. B. Kesketh and F. Swyripa, 1995)

Stop 9, figure 9 Dawson coal mine site, west of Stop 9, figure 10. Dawson coal mine site, Dawson Bridge, pre-1930 west of Dawson Bridge, 1992

(both photos from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society)

25. Stop 9b. Grierson Hill - From landslide and waste dump to

Stop 9b, figure 1. Grierson Hill Landslide, 1901

View northwest showing east flank of active failure

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society)

Stop 9b, figure 2. Grierson Hill Landslide, 1901 Home extension split from main house by landslide scarp

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society) 26. Factors affecting present-day Grierson Hill slope stability Stop 9b, figure 3. Landfill at Grierson Hill, 1931

(from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society) 27. Stop 9b, figure 4. Factors contributing to slope failure on Grierson Hill

Crest 1992 Crest 1887

Humberstone Coal Mine

Riverbank 1893 Edmonton Convention Centre

Riverbank 1984

Note!

bank over time

dumped on slump scar

(both figures from Godfrey, 1993: Edmonton beneath our feet, Edmonton Geological Society) 28. Stop 9b, figure 5. Construction of the Convention Centre on Grierson Hill Slide

Future Convention Centre

(from Godfrey, 1993: Edmonton beneath our feet,Edmonton Geological Society)

Before the Edmonton Convention Centre could be constructed in 1981, a deep excavation removed more than weight, so that no additional mass was added to the top of the slope. Deep, continuous piles were poured to support the back of the excavation before the slope was steepened by excavation. As the piles became exposed during excavation, they were anchored to the slope with long steel cables that were cemented in holes drilled through the piles and back into the slope beneath Jasper Avenue to the north. Stop 9b, figure 6. Grierson Hill Today - Stable for a while

Convention Centre

View of Grierson Hill to the north from footbridge, 1999

(photo M. Fenton AGS) 29. References and recommended readings

1. Edmonton Beneath Our Feet - A guide to the geology of the Edmonton region. Editor John D. Godfrey. Published by the Edmonton Geological Society, 1993.

Mussieux and M. Nelson. Published by The Provincial Museum of Alberta, 1998.

D.M. Cruden, R.B. Rains, and S. Thomson. Published by the Edmonton Geological Society, 1998.

4. Edmonton - The Life of a City. Editors B. Hesketh and F. Swyripa, NeWest, Publishiing Ltd., 1995.

Edmonton Geological Society publications can be obtained from the EGS web site at: www.egs.ab.ca

Rafting Services provided by: RiverWatch Science: A Not-for-Profit Education Company Contact: Cal Kullman Ph. (780) 454-4347 Fax (780)963-3378 Toll Free 1-888-933-6300

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