ABSTRACT: The 1915 and 1921 disasters at the Britannia Mine complex, Howe Sound, British Columbia; geotechnical implications for intensive resource development in steep mountain watersheds in the Coast Mountains.

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Two of Canada’s most significant natural disasters occurred at the Britannia Mine Complex in the Britannia Creek watershed located in the rugged Coast Mountains of southwest British Columbia in 1915 and 1921. The two events led to a total loss of life of 93 people and involved destruction of homes and facilities of the Britannia Mining and Smelter Company. In the 1915 disaster a catastrophic landslide at Jane Camp killed 56 people. Although this event is Canada's second largest landslide disaster in terms of loss of life no official account or scientific documentation of the disaster has ever been released or published. As a result, little is known about the landslide beyond that which is reported in contemporary newspaper accounts. Six years later, in 1921, another disaster struck the Britannia mining complex when an outburst flood resulting from the failure of a fill after heavy rains swath of destruction through the community of Britannia Beachresulting in 37 deaths. Jane Camp was established in 1903 within Jane Basin, a cirque-like bowl, on the northern side ofBritannia Mountain, within the watershed of Britannia Creek. It was located near the Portals of the Bluff Mine and at the entrance to the Jane Tunnels and in 1915 housed a substantial number of miners and miner’s families. At 00:03h on March 22, 1915, a landslide of rock, mud, and snow suddenly overwhelmed Jane Camp. 56 people were killed when the landslide smashed into a cluster of closely spaced mine buildings demolishing the mine office, cook house and diningroom, store, rock crusher, candle house and tramway terminus, together with six houses and a large bunkhouse. The Camp was buried with up to 15 m of debris. The landslide appears to have originated as a rock slope failure from the northeast side of Mammoth Bluffs, above the portal of the Bluff Mine, which subsequently developed into a debris flow. It travelled a distance of about 1.5 km down Jane Creek, reaching Britannia Creek and stopping a short distance from Tunnel Camp townsite, just over 500 m below.The source area of the initial rock slope failure and the site of Jane Camp have been removed by subsequent open pit mining, but it has been possible to reconstruct the landslide from historical photographs taken before and after the landslide, Geological Survey of Canada Map 199A for which the topography was surveyed in 1918 and 1919, and contemporary newspaper accounts. It appears that the landslide was initiated at around el. 1125 m by a small rockslide or large rock fall on a northeastfacing slope in schists of the Lower Cretaceous Gambier Group, approximately 150 m above the Camp. The initial failure may have been a block topple since the rock fabric of the Mammoth Bluffs area was dominated by schistosity that dips steeply to the southwest creating conditions favourable for toppling on northeast facing slopes. The rock mass was described as having been “forced outward” by water produced by two or three days thaw. At the base of the slope, the mass changed direction by 90 degrees to the west and travelled about 100 m down a steep slope into a flat bottomed hollow where it impacted on the mine buildings at approx. elevation 990 m. As it changed direction the debris ran up the opposite slope a distance of 5 to 8 metres. Post-slide photographs indicate a deep furrow down the slope directly below thisrun-up indicating that the rockslide mobilised a significant volume of saturated surfical deposits which appear to be bouldery till, probably through the process of undrained loading. The furrow is estimated to be an average of 30 m in width and 12 m deep and represents a volume of about40,000 cu. M. The landslide, now containing fragments of broken rock and saturated surficial materials, cut a swath about 75 m wide through the mining camp demolishing the buildings as noted above, missing the powder magazine by less than a metre. The deposit at the Camp is estimated to have been about 50,000 m3. The remainder of the debris flowed down Jane Creek tearing a great rut 15 m deep all the way down to Britannia Creek. If we assume that some 50,000 m3 travelled down Jane Creek to its confluence with Britannia Creek then a total volume of 100,000 m3 for the landslide is indicated. This should be taken as an upper limit for the volume of the landslide which appears to have consisted of about half surficial deposits and half rock. The landslide also incorporated a significant volume of snow which was estimated to be about 1.3 m deep at the site. A contemporary account describes the post-slide scene at Jane Camp scene as ‘agreat pile of mud and snow - or rather two piles , for the avalanche resembled the work of a great plow, which had furrowed through the camp throwing up, on each side a great pile of boulders, mud and broken timber, snow and ice’. These features may have been lateral levees formed when the flow changed direction another 90 degrees to the east as it turned to follow Jane Creek after wiping out the camp. Although the landslide contained large rocks, photographs of the debris alsoindicate that it also contained a significant volume of finer grained material, referred to as ‘mud’by eyewitnesses. The ‘mud’was probably incorporated into the slide from the slopeimmediately above the camp and the floor of the hollow which was described as being a little marshy. The mud was quite fluid as indicated by the fact that the interior of one of the remaining bunkhouses was plugged with mud, resulting in at least four deaths. At the time of the disaster, the Bluff Mine was in active operation. Two days before the event company personnel inspected the mountainside above Jane Camp and stated that it was "solid" . However, a remarkable contemporary photograph exists showing a gaping tension crack on theslope above the camp before the slide. These activities suggest a degree of concern existed about the stability of the rock slope prior to the disaster. A heavy snow cover existed at Jane Camp at the time of the landslide. In the Annual Report of the Minister of Mines for the Year 1915 the event is described as a “disastrous snowslide”and in several natural disaster listings this event is erroneously reported as a snow avalanche disaster. Snow was certainly incorporated into the moving mass of rock and mud, and may have contributed to the mobility of the landslide, but it was not the main constituent of the slide mass. Six years later a second disaster struck the Britannia Mine complex. At 2130 h on October 28, 1921 a sudden outburst flood struck Britannia Beach, the main living quarters site of the Britannia Mine, located on the eastern shore of Howe Sound. The flood killed 37 people in the village which formed part of the Britannia Mine complex. A wall of water reported to be 20 m high swept through the village and more than 50 houses of the 110 in the community were destroyedeither directly by the flood or by being swept out to sea. Two swaths of destruction were cut by the flood waters as it swept through Britannia Beach leaving an island of dislodged but notdestroyed houses in between. The narrower northern swath followed the immediate pre-flood stream course and the wider southern swath swept directly through a densely settled part of the settlement adjacent to the Department Store. Thirty five families, a total of 100 people were made homeless by the disaster. The disaster was preceded by 6 days of heavy rains, during which time some communities in southwestern British Columbia suffered notable flood damage. In the afternoon before the disaster, a cloudburst was noted in the mountains behind Britannia Beach leading to a dramatic increase in the discharge of Britannia Creek. Preliminary press reports suggested that the cause of the flood involved the blocking of Britannia Creek by a debris slide triggered by the heavyrainstorm and that the flood was released when the landslide dam, apparently located between a large mine railway fill (the “Tunnel Fill”, which was located at about 624 m.a.s.l, 4.8 kmupstream from Britannia Beach); and the first large artificial dam upstream, breached. According to press reports, the 15 m high Tunnel Fill had been constructed across BritanniaCreek so that the normal flow of the creek went through cribbing at the bottom of the Tunnel Fill. But in times of heavy rain, water ponded behind it with the overflow being taken through a 2.5 x 2.5 m culvert near the top of the fill. The full cause of the disaster did not become evident until the Coroner’s Inquest into the disaster held later on in November 1921. At the inquest it was established that, rather being the result of the breaching of a natural dam, the flood resulted from the collapse of the Tunnel Fill, following the ponding of water behind it when the overflow culvert in the structure became plugged. The event was, in effect, a dam-break flood. On November 28, the Coroner’s Jury found that the disaster was caused by the collapse of the Tunnel Fill, and declared that “it was criminal neglect on the part of the Britannia Mining andSmelting Co. Ltd...for deliberately allowing the blocking of.....Britannia Creek causing a menace to persons living at Britannia Beach.”. Engineers testifying at the inquest had questioned the construction of a fill structure across Britannia Creek instead of a trestle, and noted that during the unprecedented runoff, the fill had acted as a dam for which purpose it was hardly intended. It was estimated that 53,000 m3 of water was catastrophically released by the collapse of the Tunnel Fill. The events at the Britannia Mine indicate the disaster potential of intense resource developmentof a steep mountain Coast Mountain watershed where facilities are built in close proximity to steep unstable slopes and on fans at the mouth of steep creeks. The disasters may have been avoided by careful engineering design and a pre-development hazard assessment. The disasterswere the result of combined human and climatic forcing and highlights the difficulty in isolating the role of “natural” causes in some so-called natural disasters.

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