At approximately 1:28am on Monday, September 20th, 2021, a significant rockfall occurred on the north face of the Stawamus Chief, and was captured by the webcam.
In the video, rocks can be seen falling, starting just above the cloud obscuring the top of the Chief, culminating in a large slide. As the rocks descend and impact each other and the cliff wall, they emit flashes of light, clearly visible in the video footage. These flashes of light may be sparks caused by the impact of the large granite boulders into each other, or piezoelectric discharge from the quartz crystals embedded in the granite, or a combination of both.
The webcam does not capture audio, but audio of the rockfall from a nearby security camera has been added to the video, corrected for the delay caused by the speed of sound.
The rockfall originated in an area called the Upper Zodiac Wall, below Third Peak. A previous significant rockfall in April 2015 originated in the same area, but slightly higher. The rockfall in 2015 created a large talus (debris field) at the bottom of the cliff, which had started to become less apparent as vegetation had grown around it. The 2021 fall has resulted in considerable additional talus, covering the vegetation and once again being very visible when looking at the north face of the Chief.
The impact of the falling rocks were heard throughout much of Squamish, and especially in the Valleycliffe district, which is situated close to the foot of the north face of the Chief. The rockfall also caused houses nearby to shake, and seismic waves from the fall were clearly picked up by the seismograph operated by the Canadian National Seismograph Network at Watts Point, BC, located approximately 7km south-east of the Stawamus Chief near Murrin Provincial Park.
There were two additional rockfalls in the same area on the same day. The first one was at approximately 12:07am and preceeded the large rockfall by around 80 minutes, and the second one was later in the day at approximately 4:42pm. Both of these were minor in comparison to the 1:28am event.
This was the fourth major rockfall that has occurred on the Stawamus Chief during Summer 2021. The three previous rockfalls, on June 27th, July 27th, and September 10th, all fell from the Grand Wall, which faces west and is not directly visible from the webcam, although the camera did capture the resulting clouds of dust that had been thrown up. It is possible that the unusually large number of rockfalls in 2021 may have been partially caused by extreme temperatures and a very dry summer, with a new record all-time high of 43.0°C (109.4°F) being recorded in Squamish on June 28th, 2021.
Both the Grand Wall and the Zodiac Wall are popular climbing areas, and multiple areas remain closed. For the most up-to-date information on closures due to the rockfalls, visit the BC Parks website.
As regular viewers of the webcam's timelapses may be aware, it is not uncommon to see the headlamps of climbers on and around the Zodiac Wall on clear nights. Additionally, the Mamquam Forest Service Road runs very close to the base of the Chief. Fortunately, BC Parks, Squamish Fire Rescue, and Squamish RCMP reported no injuries in the area.
The daily timelapse video for September 20th, 2021 provides an overview of the day, and shows the altered appearance of the Stawamus Chief due to this rockfall.