Traffic backed up at the western edge of the Hope Slide (bottom left).

Golden Country: What caused the Hope Slide?

For many years, earthquakes were thought to be the cause. Were they?

At 3:56 a.m. on Saturday, Jan. 9, 1965, seismographs around the Pacific Northwest recorded a tremor of 3.2 on the Richter scale. The epicentre was placed within 10 kilometres of the Nicolum Valley of British Columbia, along the Hope-Princeton Highway between Johnson Peak to the north and Mount Coulter to the south.

At 6:58 a.m., seismographs recorded a second tremor—this one registering 3.1 on the Richter scale—in the same area. While the occasional small slide was not uncommon in the area during the recorded history of the region, major slides were unknown, although geologists had determined that in prehistoric times a massive slide had swept down Johnson Peak. The scars could still be seen on the landscape, thousands of years later, and a small lake—variously called Outram or Beaver Lake—had formed on the talus of the slide.

For many years it was thought that the two recordings were indicative of earthquakes which precipitated what is now known as the Hope Slide: actually two slides which swept down Johnson Peak across the Hope-Princeton and took the lives of Bernie Lloyd Beck, Dennis Arlitt, Mary Kalmakoff, and Thomas Starchuk. Beck, Arlitt, and Kalmakoff—travelling to Agassiz so that Mary could visit her sister—encountered the first slide shortly after 4 a.m. on January 9, and were soon joined by truck drivers Norm “Steph” Stephanishin and Thomas Starchuk. Steph decided to walk back to Sumallo Lodge for help, while the other four remained at the site: Starchuk to catch up on some sleep, and Beck and Arlitt to try to dig their car out while Kalmakoff waited, presumably in the cab of Steph’s truck where she could keep warm. All four were killed in the second slide which came down at the site at 6:58 a.m.; Arlitt and Kalmakoff have never been found.

Volunteers from the Hope, Princeton, and Chilliwack Search and Rescue groups, as well as Canadian Army engineers from Chilliwack, continued the search through the evening of Sunday, Jan. 10, hampered by the rocks which continued careening down the side of Johnson Peak. Late on Jan. 10 a huge cornice of rock broke off, and two Highways Department workers at the site had to dash for safety.

A final major search effort for the missing travellers was made on Jan. 11, after which the official search was called off. Bob Sowden, son of the owner of Sumallo Lodge to the east of the slide site, and one of the founders of Hope Search and Rescue, continued the search with his father, George, and his German Shepherd, Timber, for three weeks, but without success.

In the meantime, the Department of Highways under Minister Phil Gaglardi was faced with the dilemma of restoring service along the Hope-Princeton Highway, which in those pre-Coquihalla days was the main highway connecting the Lower Mainland with the Okanagan. Until service was restored, those east of the slide site faced a long journey to get to the Lower Mainland, while anyone heading east from the coast faced an equally long journey to get to their destination.

Three kilometres of highway had been wiped out by the 47 million cubic metres of debris that had filled the valley bottom, and the new ground level was in some places more than 70 metres higher than it had been. Gaglardi, who had arrived at the site on Jan. 9, initially hoped that a temporary road could be in place within 48 hours. However, as engineers got a better look at the site and made their assessments, it was clear that it would be much longer than that before the highway could be rebuilt. It is a testament to those involved that three weeks after the slide, a road had been pushed through the debris and the highway was reopened.

The new road — 55 metres above the level of the previous highway — passed directly through the slide site for part of the route before skirting the base of Mount Coulter. However, following more changes to the Hope-Princeton in the late 1980s/early 1990s, the highway now bypasses the debris field almost entirely. A rest area at the southwest edge of the slide area with information signs now affords the best view of the site.

The Hope Slide remains the largest recorded landslide in Canadian history, based on the amount of debris. By contrast, the deadliest slide in Canadian history—the Frank, Alberta slide of 1903, which killed between 70 and 90 people—involved a fall of 30 million cubic metres of debris. That the Hope Slide was not responsible for more deaths—even though it came down across a major highway—can probably be attributed to the low number of travellers on the highway in the early hours of a cold January morning.

The cause of the slide has long been attributed to earthquake activity in the Nicolum Valley, as indicated by the tremors recorded at 3:56 and 6:58 a.m. on Jan. 9. However, more recent studies have determined that what the seismographs picked up were not earthquake tremors that caused the slide; rather, the tremors that were recorded were caused by the force of the fall of the two slides and their impact on the valley floor.

So what caused this catastrophic failure on the slope of Johnson Peak? The actual trigger is still unclear. Changes in groundwater condition are often the trigger for slides, but the Hope Slide occurred during a prolonged period of sub-zero temperatures in the area. For more than three weeks prior to the slide, the weather had been much colder than usual, with the daily temperature never exceeding 0° C, and hovering around -10° C most days.

It is now believed that there must have been pre-existing faults and shear zones on the southwestern slope of Johnson Ridge, and it has been suggested that the cold weather caused the prolonged freezing of water in the seepage exit points at the toe of the slide, resulting in an increase in water pressure there. Continued weathering and ongoing tectonic activity in the area weakened the slide mass over time, and caused the ongoing, unnoticed deterioration of the slope’s stability. Plainly put, the Hope Slide was not caused by earthquakes: it was the natural, tragic, result of a long-term series of events which culminated in catastrophe in the early morning hours of Jan. 9, 1965.

To be continued



editorial@accjournal.ca

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