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Geoscience Canada

International Year of Planet Earth 8. Natural Hazards in Canada John J. Clague and Peter T. Bobrowsky

Volume 37, Number 1, January 2010 Article abstract Canada, the second largest country in the world, is subject to every hazardous URI: https://id.erudit.org/iderudit/geocan37_1ser01 natural process on Earth − large earthquakes, tsunami, volcanic eruptions, landslides, snow avalanches, floods, hurricanes, tornados, severe storms, See table of contents drought, and sea-level rise. Fortunately, much of the country is sparsely populated; hence risk from these hazardous processes is localized to small areas adjacent to the Canada−US border, where most Canadians live. The Publisher(s) greatest risk comes from earthquakes and landslides on the populated south coast of British Columbia and parts of southern Ontario and Québec; from The Geological Association of Canada floods in Vancouver, Calgary, Winnipeg, or Toronto; and from hurricanes in Halifax and St. John’s. In the long term, Canada’s coastlines are threatened by ISSN sea-level rise and Canada’s northern indigenous peoples are threatened by permafrost thaw caused by global warming. 0315-0941 (print) 1911-4850 (digital)

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Cite this document Clague, J. J. & Bobrowsky, P. T. (2010). International Year of Planet Earth 8. Natural Hazards in Canada. Geoscience Canada, 37(1), 17–37.

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Calgary, Winnipeg, or Toronto; and period, and up to 24 m snow per year from hurricanes in Halifax and St. (Hare and Hay 1974; Hare and John’s. In the long term, Canada’s Thomas 1974). The size of the country coastlines are threatened by sea-level and the diversity of its environments rise and Canada’s northern indigenous ensure that it regularly experiences a peoples are threatened by permafrost wide range of natural hazards (Clague thaw caused by global warming. 1991; Brooks 2001; Liverman et al. 2001). SOMMAIRE Size and diversity, however, are Deuxième plus grand pays de la only part of the natural hazards story. planète, le Canada est exposé à chacun Canada has experienced the same International Year of des risques naturels sur Terre – grands demographic trends as much of the séismes, tsunamis, éruptions vol- rest of the world − a growing popula- Planet Earth 8. caniques, glissements de terrain, ava- tion concentrated primarily in urban Natural Hazards in Canada lanches de neige, inondations, oura- centres, and much of its economic gans, tornades, fortes tempêtes, sécher- productivity and wealth localized in esses, et hausse du niveau de la mer. potentially hazardous areas. It should John J. Clague Heureusement, le pays est peu peuplé therefore come as no surprise that Centre for Natural Hazard Research, en grande partie, et donc, le risque losses from natural disasters, both Simon Fraser University associé à ces phénomènes naturels est globally and in Canada, are increasing Burnaby, BC, Canada, V5A 1S6 restreint à des bandes étroites le long (Fig. 1). Email: [email protected] de la frontière séparant le Canada et les The United Nations designat- États-Unis, là où la plupart des Canadi- ed the 1990s as the International Peter T. Bobrowsky ens vivent. Les risques les plus élevés Decade for Natural Disaster Reduction Geological Survey of Canada, proviennent des séismes et des glisse- (IDNDR). The objectives of the Natural Resources Canada ments de terrain le long de la côte sud IDNDR program were to minimize 601 Booth Street, peuplée de la Colombie-Britannique et loss of life and property damage from Ottawa, ON, Canada, K1A 0E8 certaines portions du sud de l’Ontario natural disasters, but the objectives et du Québec; d’inondations dans les were not met; rather, losses from disas- SUMMARY villes de Vancouver, Calgary, Winnipeg, ters increased dramatically in the 1990s, Canada, the second largest country in et Toronto; et, d’ouragans à Halifax et mostly because of global population the world, is subject to every haz- à Saint-Jean. Au long terme, les côtes growth, much of it in areas prone to ardous natural process on Earth − canadiennes sont exposées à la hausse natural hazards. Yet, since 1995, the large earthquakes, tsunami, volcanic du niveau de la mer, et les peuples world has experienced the devastating eruptions, landslides, snow avalanches, autochtones du Nord canadien sont tsunami in the Indian Ocean; flooding floods, hurricanes, tornados, severe menacés par le dégel du pergélisol in Manitoba, Bangladesh, and central storms, drought, and sea-level rise. découlant du réchauffement climatique. Europe; huge debris flows in Fortunately, much of the country is Venezuela; one of the strongest El sparsely populated; hence risk from INTRODUCTION Niños on record; and deadly earth- these hazardous processes is localized Canada extends over about10 million quakes in Japan, India, Iran, Turkey, to small areas adjacent to the Cana- km2, making it the second largest coun- Pakistan, China, and most recently, da−US border, where most Canadians try in the world. It has 243 000 km of Haiti and Chile. In the same period, live. The greatest risk comes from coastline bordering three oceans, eleva- Central America experienced a deadly earthquakes and landslides on the pop- tions ranging from sea level to 5959 m Category 5 hurricane; New Orleans ulated south coast of British Columbia on Mt. Logan, and is subject to was devastated by Hurricane Katrina; and parts of southern Ontario and extreme weather conditions; –63°C to British Columbia and several of the Québec; from floods in Vancouver, 45°C; up to 49 cm of rain in a 24-hour western US states experienced record- 18

overburden, is not discussed, but the interested reader is referred to an earli- er paper in this series (Rasmussen and Gardner 2008) and references therein. For lack of space, we do not discuss climate change as a hazard per se, but we do comment on the significance of climate change in terms of other haz- ards. We discuss the character and dis- tribution of each hazard, provide examples of past disasters, and attempt to extract broader implications from past events.

EARTHQUAKES Earthquakes are one of the greatest natural hazards that humans face. Dur- ing the 20th century alone, over two million people died during earthquakes and attendant fires, tsunamis, and land- slides (Keller et al. 2008). Recently, in January 2010, an earthquake in Haiti killed about 23 000 people and, earlier, Figure 1. Estimated damage (in billions of US dollars) caused by natural disasters in December 2004, more than 225 000 between 1900 and 2007. Source: EM-DAT, the Office of US Foreign Disaster people in eleven countries lost their Assistance/Centre for Research on the Epidemiology of Disasters lives to the tsunami triggered by the (OFDA/CRED), International Disaster Database, [www.emdat.be], Université magnitude (M) 9.3 earthquake off the Catholique de Louvain, Brussels, Belgium. west coast of Sumatra in Indonesia. In December 2003, the ancient city of setting wildfires; an ice storm crippled property damage. Severe weather Bam in Iran was levelled by an M 6.1 Ontario, Québec, and New England; events cause the largest number of earthquake, with the loss of almost 30 and Earth experienced many of the deaths each year, although floods and 000 lives. The worst disaster in modern warmest years of the past 100 years landslides also take a toll. Loss of life times occurred in China in July 1976, and possibly of the past 1000 years. from earthquakes in North America is when the entire city of Tangshan was These and other events are the result surprisingly low, largely because of the destroyed and over 240 000 people of enormous forces that are at work high standards of building construc- were killed in less than six minutes. both inside and on the surface of our tion. But a single large earthquake can Earlier, in 1556, an earthquake in planet. cause tremendous property damage. north-central China near Shaanxi killed To a far greater degree than For example, the Northridge earth- an estimated 800 000 people, one of the public at large, the earth science quake in Los Angeles in 1994 caused the worst natural disasters in recorded community is aware that earthquakes, US$20 to 30 billion in property dam- history (Keller et al. 2008; United tsunami, volcanic eruptions, landslides, age, but killed only 60 people. The States Geological Survey 2009a). For- floods, and fires are natural processes next great earthquake in a densely pop- tunately, catastrophes of this scale do that have been occurring on Earth for ulated part of California or in Seattle not occur in Canada, not because large billions of years. These processes are or Vancouver could cause US$100 to earthquakes do not occur in this coun- only hazardous when they threaten 200 billion in damage. try, but rather because buildings and human beings. A ‘hazard’ thus can be The purpose of this paper is other infrastructure are less vulnerable defined as a natural process that threat- to review the suite of natural hazards to life-threatening collapse and fewer ens human life or property. A related that most affect Canadians. We take a people are exposed to natural hazards. concept, ‘risk’, may be expressed as the broad view of natural hazards by probability that a destructive event will including not only classic geologic haz- Locations and Types of Earth- occur multiplied by the event’s likely ards−earthquakes, tsunami, volcanic quakes in Canada impact on people and property. Risk eruptions, and landslides−but also Earthquakes are not randomly distrib- thus integrates hazard and social and briefly look at hydro-meteorological uted. Most occur in well defined zones economic vulnerability. hazards, including severe weather phe- along the boundaries of Earth’s tec- When we compare the effects nomena (floods, hurricanes, tornadoes, tonic plates. In Canada, earthquakes of different natural hazards in North blizzards, snow avalanches, hailstorms, are most common in coastal British America, we find that those that cause ice storms, drought, and heat waves). Columbia near the western edge of the the greatest loss of life are not the Radon hazard, primarily related to the North America plate (Rogers and same as those that cause the most abundance of uranium in bedrock and Horner 1991), but they also occur in GEOSCIENCE CANADA Volume 37 Number 1 March 2010 19 many other parts of the country, notably southwest and eastern Yukon Territory, southern Ontario and Québec, and some of the Arctic Islands (Fig. 2). Plate-boundary earthquakes occur along convergent, divergent, and transform plate boundaries. In Canada, plate-boundary earthquakes are restricted to the Pacific coast and are of two types. Subduction earthquakes occur along the thrust fault separating the North America and Juan de Fuca plates (Rogers 1988; Hyndman 1995; Hyndman et al. 1996). Subduction earthquakes occur when the strain energy that has accumulated in rocks adjacent to the convergent plate- boundary fault is suddenly released (Dragert et al. 1994; Hyndman and Wang 1995). The last great subduction earthquake on the Pacific coast, in Jan- uary 1700, left geological traces in tidal marshes in northern California, Ore- gon, Washington, and British Columbia (Atwater et al. 1995, 2005; Atwater and Hemphill-Haley 1997; Clague 1996, Figure 2. Epicentres of earthquakes in Canada, 1627–2007 (M > 2.5). Source: 1997, 2002; Clague and Bobrowsky Geological Survey of Canada. 1994a, b, 1999; Nelson et al. 1995, 2006). Its inferred extent, together with China. Moderate and large intraplate continent, which lies along the St. written records of the damage caused earthquakes in densely populated areas Lawrence River valley from Montreal by its tsunami in Japan (Satake et al. are extremely destructive; they can to Sept Sles, Québec; related rift struc- 1996; Atwater et al. 2005), indicate that claim tens of thousands of lives and tures also occur along the Ottawa and the quake likely had a magnitude larger may cause damage assessed in the tens Saguenay river valleys. Strain accumu- than M 9.0. or hundreds of billions of dollars. lates on these structures due to the The second type of plate- Because large (M >7) intraplate quakes westward movement of the North boundary earthquake on the west coast are infrequent, most people are gener- American Plate away from its eastern involves strike-slip or oblique-slip dis- ally poorly prepared for them and margin at the Mid-Atlantic Ridge. placements along the Queen Charlotte older buildings may not be able to Earthquakes along the rift involve Fault, which separates the Pacific and withstand the associated strong shak- thrust movements at depths of 5 to 30 North America plates and extends ing. Canada’s largest intraplate earth- km and occur in three clusters (Fig. 2): from the north end of Vancouver quake is the M 7.3 Vancouver Island western Québec, which experienced Island to the southeast Alaska archipel- quake in 1946, which was felt as far moderate earthquakes in 1732 (M 5.8), ago. The Queen Charlotte Fault is con- away as Seattle, Washington, and Cal- 1935 (M 6.2), and 1944 (M 5.8); tiguous to the north with the Fair- gary, Alberta (Rogers and Hasegawa Charlevoix, northeast of Québec City weather Fault, and the latter extends 1978). Fortunately, the epicentral area (1663, 1791, 1860, 1870 and 1925; M along the coast of southeast Alaska to in 1946 was sparsely populated, hence 6.0−7.0); and the lower St. Lawrence a block of complexly deforming crust damage was minor compared to what a region near Baie-Comeau, Québec, (Yakutat Block) located east of the similarly sized earthquake in the same comprising a diffuse cluster of mostly Aleutian Trench. Canada’s largest area would cause today. A shallow, M 7 small earthquakes (Lamontagne 2002). recorded earthquake, an M 8.1 event, crustal earthquake close to Vancouver The most recent and widely felt earth- ruptured a portion of the Queen Char- or Victoria would now cause cata- quake in central Canada in recent time lotte Fault in 1949 (Milne et al. 1978). strophic damage (Munich Reinsurance occurred in the Saguenay region of Intraplate earthquakes occur Company of Canada 1992). Québec in 1988 (M 5.9). on faults within, rather than between, Moderate-size intraplate earth- plates. Although commonly smaller quakes occur frequently in southern Damaging Effects than subduction earthquakes, some Ontario and Québec (Adams and Historical large earthquakes in Canada intraplate earthquakes have moment Basham 1989, 2001). Most of these have caused little damage by California magnitudes in the M 7.5−8.0 range, quakes are associated with the ancient standards. The M 8.1 Queen Charlotte e.g. the May 2008 quake in southwest rifted edge of the North American Islands earthquake in 1949 was larger 20 than the 1906 San Francisco earth- in an earthquake. may topple when shaken, producing quake, yet caused little damage and no Intense seismic shaking can gas leaks that can ignite. The San Fran- loss of life because no more than a elevate intergranular pore-water pres- cisco earthquake of 1906 has often few thousand people lived in the area sure in loose, water-saturated sedi- been referred to as the ‘San Francisco of strong ground shaking at the time ments and cause them to liquefy. Liq- Fire,’ because most of the damage and of the quake. Similarly, the epicentre of uefaction commonly takes place at loss of life were caused by a firestorm the 1946 Vancouver Island earthquake shallow depths and is most common in that ravaged the city for several days (M 7.3) was far enough from towns loose sandy and silty sediments (Jef- following the quake. Such a firestorm and other infrastructure that the dam- feries and Been 2006). Liquefaction is unlikely to happen in a Canadian city age was limited. Today, the same area may be accompanied by lateral shifts of today, but localized fires can be expect- supports a much larger population and more cohesive earth materials on one ed in the event of a large (M 7+) event far more economic wealth than in or more layers of fluidized sediment, close to an urban centre. 1946, so if the same event were to causing much damage to roads and occur now, financial damage would buildings at the surface and to gas, TSUNAMI likely be in the hundreds of millions of water, and sewer lines buried at shallow Historic Events dollars, if not more. depth. Watery sand and silt may also The west coast of Canada is located The intensity of seismic shak- flow, under pressure, upward along fis- along the Pacific ‘Ring of Fire’ and is ing is commonly expressed as the ratio sures in overlying solid materials and vulnerable to tsunami generated by of ground acceleration to the accelera- onto the surface to form ‘sand blows’ subduction earthquakes that occur tion of gravity (Bolt 2003). Strong or ‘sand volcanoes’. Liquefaction caus- beneath the Pacific Ocean (Murty ground shaking can be especially dam- es the land surface to settle irregularly, 1977; Clague et al. 2000, 2003). The aging to a building if the horizontal which, in turn, may damage founda- largest tsunami results from great component of motion is strong or if tions of buildings, water and sewer earthquakes that rupture the Cascadia the frequency of the shaking matches lines, and other structures. plate boundary where the oceanic Juan the natural vibration frequency of the Some earthquakes raise or de Fuca Plate moves beneath North building, a phenomenon called ‘reso- lower the land over large areas. The America (Fig. 3). The British Columbia nance’. In general, high-frequency, Cascadia subduction earthquake in coast is also affected by tsunami of short-period seismic waves are most 1700 caused parts of the Pacific coasts more distant Pacific earthquakes. In damaging to low structures, whereas of Vancouver Island, Washington, and fact, the largest tsunami to strike low-frequency, long-period waves tend Oregon to subside up to 2 m, inundat- British Columbia in historical time was to damage tall buildings or long struc- ing coastal marshes and forests with generated by the M 9.2 Alaska earth- tures such as bridges. sea water (Peterson et al. 1997). A large quake in March 1964 (Plafker 1969; The characteristics of local crustal earthquake near Seattle about Lander 1996). A series of waves radiat- earth materials strongly influence the 1000 years ago produced co-seismic ed outward from the epicentre of the frequency distribution of wave forms uplift of up to 7 m (Bucknam et al. earthquake off south-central Alaska and ground-motion attenuation during 1992). and, within a few hours, reached the an earthquake (Bolt 2003). The dense Large earthquakes may also outer coast of British Columbia. The granitic and metamorphic rocks of the trigger hundreds or thousands of land- tsunami caused about $10 million dam- Canadian Shield can transmit earth- slides. The 1970 Ancash earthquake in age (1964 dollars), mainly to the Van- quake energy very efficiently, and even Peru (M 7.9) triggered a huge landslide couver Island communities of Port moderate earthquakes can therefore that destroyed the towns of Yungay Alberni, Hot Springs Cove, and Zebal- cause damage over large areas. In con- and Ranrahirca, killing thousands of los (Wigen and White 1964; Murty and trast, seismic energy and associated people (Plafker and Ericksen 1978). A Boilard 1970; Murty 1977; Thomson ground shaking attenuates rapidly away large (M 7+) earthquake in southern 1981). Damage was greatest at Port from the epicentres of most earth- Québec in 1663 triggered ‘quick clay’ Alberni, located at the head of Alberni quakes in the extremely heterogeneous, failures in glacial marine sediments in Inlet, where 260 homes in the town folded, and faulted crust of western the St. Lawrence River valley (Filion et were damaged, 60 of them extensively North America. Seismic waves also al. 1991), and the 1946 Vancouver (Thomson 1981). move much more slowly through loose Island earthquake triggered hundreds Tsunami of more local extent, sediments than through bedrock, espe- of mainly small landslides in the triggered by landslides and shallow cially if the sediments have high water mountains of central Vancouver Island crustal earthquakes, also pose a hazard content. For example, seismic waves (Mathews 1979). to Canada’s west coast, especially in typically slow down as they move from Ground shaking and surface steep-walled fiords and inlets that bedrock to alluvial sands and gravels. rupture can sever power, telecommuni- indent the coast (Clague 2001). A sub- As P (primary) and S (secondary or cation, and gas lines, starting fires. marine landslide in April 1975 at the shear) waves decelerate, some of their Such fires may be difficult to suppress head of an inlet on the northern forward-directed energy is transferred because fire-fighting equipment may be British Columbia coast produced waves to surface waves. This effect, known as damaged; streets, roads, and bridges up to 9 m high that damaged wharfs seismic amplification, increases the blocked; and water mains broken. and other shoreline infrastructure at amount of ground motion experienced Appliances such as gas water heaters Kitimat (Murty 1979; Prior et al. 1982, GEOSCIENCE CANADA Volume 37 Number 1 March 2010 21

1984; Johns et al. 1986; Skvortsov and Bornhold 2007). More than 10 million m3 of fiord-wall and deltaic sediments failed and flowed into the inlet, mobi- lizing an additional 25 million m3 of fiord-bottom sediments. The subaque- ous debris flow travelled over 5 km from the delta front on slopes inclined less than 0.4° to a water depth of 210 m (Prior et al. 1984). Similar unstable sediments are present in most fiords on the British Columbia coast; local, landslide-triggered tsunamis are there- fore also possible in many areas other than Kitimat Inlet. Tsunami can also be triggered by rockfalls and rockslides from the walls of British Columbia fiords. Born- hold et al. (2007) proposed that the Figure 3. Schematic diagram showing generation of a tsunami by displacement First Nations village of Kwalate in along the fault separating the North America and Juan de Fuca plates during a Knight Inlet was destroyed by a local great earthquake at the Cascadia subduction zone (Clague et al. 2006, p. 130). The tsunami triggered by the catastrophic largest and most energetic waves travel east and west from the seafloor rupture. failure of a nearby steep rock wall Smaller waves move away from the fault in other directions. about 500 years ago. Fortunately, most of British Columbia’s coastal residents live along the Strait of Georgia, an area of low tsunami risk (Fig. 4). The total popula- tion in communities at higher risk, on western Vancouver Island (e.g. Tofino, Ucluelet, Port Alberni) and at fiord heads (e.g. Kitimat, Bella Coola), is less than 10 000, and small in comparison to the population of tsunami-prone areas on the Pacific coasts of Oregon and Washington. A large submarine landslide can also generate a tsunami, as hap- pened at the edge of the Canadian Atlantic continental shelf on Novem- ber 18, 1929. On that day, an M 7.2 earthquake occurred about 20 km beneath the seafloor at the southern edge of the Grand Banks, some 250 km south of Newfoundland (Heezen and Ewing 1952; Piper et al. 1988). Earthquake shaking triggered a huge submarine slump, which, in turn, set off a tsunami that propagated across the Atlantic Ocean (Fine et al. 2005). The tsunami damaged more than 40 coastal communities on Burin Peninsu- la and claimed 27 lives in Newfound- land and one in Nova Scotia (Whelan 1994). The tsunami arrived near the Figure 4. Tsunami hazard zones in coastal areas of southwestern British Columbia peak of a high tide, thus increasing the (Clague et al. 2006, p. 138). Western Vancouver Island is at risk from large tsunami damage. triggered by great subduction earthquakes beneath the Pacific Ocean. The tsunami Landslides may also generate risk in the Strait of Georgia is much lower and is related to crustal earthquakes and destructive displacement waves and subaqueous landslides. Local, landslide-triggered tsunami pose a hazard to some seiches in lakes and rivers bordered by coastal communities, especially those at the heads of fiords. 22 steep, unstable slopes and in lakes con- The sand sheets become thinner and canology and Chemistry of the Earth’s taining actively growing deltas. Such finer in a landward direction, and com- Interior, Subcommittee on Decade events can cause much damage and monly contain marine microfossils, Volcanoes 1994). Several active or loss of life. For example, in 1880, a indicating that they were deposited by potentially active volcanoes in western large mass of late Pleistocene glacial strong landward surges of water. Some North America lie near cities with pop- marine sediments slid into the Fraser of the sand sheets directly overlie ulations of over 500 000 people. More River at Haney, east of Vancouver, buried peaty or forest soils that sub- than 90 percent of Canada is risk-free producing a displacement wave that sided during great earthquakes at the from local volcanic activity, but a huge travelled several tens of kilometres up Cascadia subduction zone (Atwater et ‘supervolcano’ eruption in the Yellow- and down the river, causing consider- al. 1995; Clague and Bobrowsky 1994a, stone volcanic field in Wyoming–Mon- able damage to boats, wharves, and b, 1999; Clague 1997, 2002). Analogues tana, the Long Valley caldera in Cali- buildings at the shore (Evans 2001). for these prehistoric subduction earth- fornia, or the Aleutian Arc in Alaska And in August 1905, a landslide in quakes include the great earthquakes in would likely have an impact through- Pleistocene glacial lacustrine sediments Chile in 1960, Alaska in 1964, and out North America in the form of ash crossed the Thompson River near Indonesia in 2004, each of which pro- fall and ash clouds in the atmosphere. Spences Bridge in southwestern British duced widespread crustal subsidence in Supervolcano eruptions expel more Columbia, producing a 5-m-high dis- their source areas and destructive far- than 1000 km3 of ejecta, in contrast to placement wave that rushed more than travelled tsunami. the 4 km3 of ejecta erupted at Mount 1.5 km upstream, destroying twenty Tsunami deposits also have St. Helens in May 1980 and the 30–35 buildings and drowning 15 people been found in nearshore coastal lakes km3 erupted from Mount Katmai in (Evans 2001). Three years later, in in Oregon and on western Vancouver 1912 (Wood and Kienle 1990; United 1908, a landslide on the Liève River in Island (Hutchinson et al. 1997, 2000; States Geological Survey 2005, 2009b). western Québec generated a displace- Clague et al. 1999; Kelsey et al. 2005). Even a small explosive eruption, how- ment wave that inundated part of the Tsunamis enter the lakes by surging up ever, could disrupt air travel in Canada. village of Notre-Dame-de-la Salette, outlet streams or by crossing sand Young volcanoes in Canada killing 27 people (Evans 2001). dunes that lie between some of the are restricted to British Columbia and Tsunami height and run-up lakes and the sea. The most complete southern Yukon Territory (Souther depend on the distance from the record found to date is from Bradley 1970, 1977; Hickson and Edwards source, possible resonance amplifica- Lake in Oregon, where there are 14 2001; Fig. 6). Several eroded stratovol- tion in inlets and bays, tidal height at tsunami layers in a sequence spanning canoes in southwestern British Colum- the time of the tsunami, shoreline con- the last 7500 years (Fig. 5; Kelsey et al. bia form the northern part of the Cas- figuration, and the gradient of the 2005). cade volcanic chain, which owes its ori- seafloor directly off the coast. Numeri- So far, evidence for a prehis- gin to subduction of the oceanic Juan cal modelling by Chasse et al. (1993) toric tsunami has been found only on de Fuca Plate beneath North America. has shown that the maximum ampli- Canada’s west coast, but similar evi- They include Mount Garibaldi, Mount tude of a tsunami in the St. Lawrence dence likely exists in Atlantic Canada. Cayley, and Mount Meager, but only Estuary would be about 1.5 m. Such a A widespread layer of 8000-year-old Mount Meager has had an eruption in tsunami, however, could reach up to sand, which has been found in coastal the Holocene. Similar volcanoes are 4.5 m above sea level (asl) at the high- areas of eastern Scotland, western also present in the boundary area est tide, or only 0.9 m asl at the lowest Norway, and Iceland, was deposited by between Alaska and the Yukon, north tide. Also, the tsunami would travel a large tsunami triggered by a subma- of the Aleutian Trench. much faster along the north side of rine landslide in the North Atlantic A large number of Pleistocene the estuary, due to the greater water Ocean (Dawson et al. 1988; Bondevik and postglacial volcanoes occur within depth, than along the south side. Simi- et al. 1997). On the basis of the known a broad, north-trending belt in north- lar dependence of speed on propaga- extent and character of the landslide western British Columbia and south- tion direction was noted during the deposit, the tsunami may have been ernmost Yukon (Fig. 6; Souther 1970, 1929 Grand Banks tsunami − it took large enough to impact and leave a 1977; Hickson and Edwards 2001). much longer for the tsunami to reach trace along the Atlantic coast of Cana- Most of these volcanoes are small and Nova Scotia than Newfoundland, even da. the product of one or a few effusive though Nova Scotia was closer to the eruptions of basaltic magma, but tsunami source (Berninghausen 1968). VOLCANIC ERUPTIONS Mount Edziza and Hoodoo Mountain Approximately 500 million people live have been formed by numerous erup- Prehistoric Events close to volcanoes, and as the human tions over a long period of time, and Sand sheets deposited by prehistoric population continues to grow, this some of the eruptions were explosive. tsunami have been found in mud and number will increase. In the past 100 Scientists believe that volcanism in peat deposits in protected tidal marsh- years, nearly 100 000 people worldwide northwestern British Columbia is the es at many sites on western Vancouver have been killed by volcanic eruptions; result of crustal rifting caused by right- Island, Washington, and Oregon approximately 28 500 lives were lost in lateral displacements on the Queen (Clague and Bobrowsky 1994a, b, 1999; the 1980s alone (Wright and Pierson Charlotte and Fairweather faults to the Clague 1997, 2002; Peters et al. 2007). 1992; International Association of Vol- west (Hickson and Edwards 2001). A GEOSCIENCE CANADA Volume 37 Number 1 March 2010 23

Figure 5. Stratigraphy of Holocene sediments in Bradley Lake, Oregon, showing 14 sand layers interpreted to have been deposited by tsunamis triggered by great earthquakes in the eastern North Pacific Ocean (Kelsey et al. 2005, Fig. 4). third group of volcanoes extends in a ward−Nazko volcano is only 8000 that the volcanoes formed on the west- westerly direction from Nazko in cen- years old, whereas the dikes that fed ward-moving North America plate tral British Columbia to the Pacific former volcanoes on the British over a hot spot in the mantle (Fig. 6; coast near Bella Coola. Volcanoes in Columbia coast are Miocene. The sim- Rogers and Souther 1983). A group of this last group increase in age west- plest interpretation of this pattern is small, mainly basaltic volcanoes, some 24

est concern at Mount Baker are ash falls, landslides, volcanic mudflows (lahars), and infilling of river valleys with sediment. A major eruption of Mount Baker could spread ash over Vancouver, Abbotsford, Chilliwack, and other cities and towns in southern British Columbia. The ash would at least temporarily paralyze air and ground traffic and could impact water quality. The rocks around Mount Baker’s summit crater have been exten- sively altered to soft clay minerals by circulating hot acidic groundwater. These altered rocks would likely fail if the volcano became inflated with magma at the onset of an eruption, but a large landslide could occur on the steep flanks of the volcano even without an accompanying eruption, given the steepness of the slopes and the weakness of the rocks. Such land- slides could range in size from small debris avalanches and debris flows to massive collapses of the entire summit or sides of the volcano. During an eruption of Mount Baker, hot volcanic debris would mix with water melted from snow and ice on the summit and flanks of the mountain to form large lahars that would surge down adjacent river valleys. A lahar or series of lahars, moving down the Nooksack River on the north side of Mount Baker, could carry sufficient debris and water to spill into British Columbia at Sumas (Fig. 8).

LANDSLIDES Thousands of landslides occur annual- ly in Canada. Fortunately, most of Figure 6. Recent volcanic activity in western Canada occurs in three tectonic set- them are either small or occur in tings: 1) along convergent plate boundaries where one plate subducts beneath remote areas distant from towns and another (e.g. Mount Garibaldi and Mount Meager); 2) in regions where the North other infrastructure. Nonetheless, land- American plate is rifting (e.g. Mount Edziza and the Iskut River area); and 3) at hot slides have claimed, on average, about spots where upwelling magma breaks through the crust (e.g. Nazko). Zones of dif- four lives each year in Canada over the ferent types of volcanism are circled. Source: Geological Survey of Canada. past 150 years (Evans 1999). Nearly half of the historic loss of life is of which are Holocene in age, occur in State, is a stratovolcano formed by attributable to two disasters, one in eastern British Columbia in Wells Gray numerous eruptions over the past 50 April 1903 at Frank, Alberta, and the Provincial Park. Many of the volcanoes 000 years. The conical shape of Mount second near Britannia, British Colum- have unusual morphologies as a result Baker reflects its status as an active bia, in March 1915. The Frank slide of their formation beneath the ice volcano (Fig. 7). It most recently erupt- destroyed much of the community of sheets that episodically covered the ed in 1843, and venting of gases and Frank and killed about 75 of its resi- area. hot fluids from the summit crater in dents (Fig. 9; McConnell and Brock The volcano that poses the the late 1970s provided a timely 1904; Cruden and Krahn 1973). It greatest risk to Canada is actually locat- reminder that the volcano remains resulted from the sudden failure of a ed in the United States. Glacier-cloaked ‘armed and dangerous’. large (ca. 30 million m3) mass of Paleo- Mount Baker, in northern Washington The volcanic hazards of great- zoic limestone on Turtle Mountain. GEOSCIENCE CANADA Volume 37 Number 1 March 2010 25

Although the primary cause of the fail- ure was geological, i.e. weak planes in the folded and faulted sedimentary rocks, the trigger may have been underground coal mining at the base of the mountain. Turtle Mountain was also predisposed to failure because the toe of the slope had been eroded by Pleistocene glaciers (Jackson 2002). The 1915 Britannia slide (ca. 100 000 m3) was much smaller than the land- slide at Frank, but it claimed nearly as many lives (Clague and Turner 2003). An estimated 56 people were killed when a sudden avalanche of rock over- whelmed a makeshift mining camp located about 8 km east of the town of Britannia. As in the case of the Frank slide, mining probably contributed to the failure. Although the total loss of life in Canada from landslides is relatively Figure 7. Mount Baker, an active stratovolcano, looms above the Vancouver sky- low, damage to infrastructure and sec- line. It last erupted in 1843. A major eruption today would melt the glaciers on ondary losses probably exceeds $200 Mount Baker, causing floods and lahars in the valleys that extend off the flanks of million annually (Geological Survey of the volcano. Photo by J. Clague. Canada, unpublished data, 2010). Much of the loss results from closure and clearing of highways and rail lines. An extreme example is the huge (48 mil- lion m3) Hope slide, which buried Highway 3 in southern British Colum- bia to a depth of 80 m on January 9, 1965 (Mathews and McTaggart 1978); the highway was closed for weeks.

Distribution Landslides occur in all provinces and territories in Canada, as well as on the seafloor off the Pacific, Atlantic, and Arctic coasts, but their incidence is highest in the mountainous parts of the country – the Cordillera of British Columbia, Yukon, and Alberta, and the Appalachian provinces of Québec and New Brunswick (Mollard 1977; Evans 2001). Areas at risk from landslides in other parts of the country are local- ized, notably in parts of the St. Lawrence Valley underlain by Leda Clay, and along glacial meltwater valleys Figure 8. A large lahar moving down the Nooksack River valley from Mount eroded into shales and clays on the Baker would spill into British Columbia at Sumas (Clague et al. 2006, p. 140). Prairies. Leda Clay was deposited in an arm of the sea that occupied the St. sediment, leading to liquefaction and small in comparison to many other Lawrence Valley at the end of the last landslides. types of landslides. Most debris flows glaciation. Its constituent clay minerals Some of the most damaging are funnelled along steep stream chan- are weakly bound to one another; an landslides in Canada are debris flows – nels and ravines and are triggered by apt metaphor for the sediment is a watery slurries of silt, sand, gravel, and intense rainstorms or rain-on-snow ‘house of cards’. When disturbed, woody debris. They range in volume events (VanDine 1985; Jakob and grains may collapse and become sus- from several hundred cubic metres to Weatherly 2003). They are common in pended by water in the pores of the about 100 000 m3, and therefore are the mountains of western British 26

Figure 9. The 1903 Frank slide is Canada’s best-known landslide and a classic example of a rock avalanche. It travelled more than 3 km in 100 sec- onds and buried part of the mining town of Frank, Alberta, killing about Figure 10. Aftermath of a debris flow that swept down Alberta Creek and 75 people. Coal mining at the base of through the community of Lions Bay in February 1983, killing two people. Source: the mountain likely triggered the land- Vancouver Sun. slide. Geological Survey of Canada photo. struction of debris catch basins and in the snowpack, snowfall amounts and new highway bridges, lining of stream type, and wind (McClung and Schaerer Columbia, but are by no means channels, and channel clearing. The 1993; Jamieson 2001). Weak layers in restricted to that area. catch basins trap debris before it reach- the snowpack can form in three main Events following establish- es the highway, rail line, and homes. ways (Jamieson 2006). First, wind can ment of the community of Lions Bay, The other protective works allow contribute to the rapid build-up of located along Howe Sound between debris flows to travel unimpeded along snow (wind slabs) on sheltered lee Vancouver and Squamish, illustrate the channels through communities. The slopes. If winds become stronger dur- problems that debris flows can cause. total cost of these works has been esti- ing a snowstorm, a dense layer of bro- Development at Lions Bay began in mated at $12–17 million (1985 dollars; ken and packed snow crystals (hoar) 1957 during construction of Highway Jackson et al. 1985). may accumulate on a delicate layer of 99. Most of the community is located unbroken crystals that had fallen earlier on a late Pleistocene fan and on adja- SNOW AVALANCHES in the storm. In this manner, the layer cent rock slopes, but about 63 houses A snow avalanche is a slide or flow of of unbroken crystals becomes a buried are situated on the coalesced Holocene snow down a mountainside. The snow weak surface along which failure may fans of Harvey and Alberta creeks. On mass may travel as a coherent block, subsequently occur. Second, surface February 11, 1983, a disastrous debris deforming and fragmenting along its hoar, also called hoar frost, may form flow swept down Alberta Creek into path, or it may rapidly disaggregate on cold clear nights by sublimation. Ice Lions Bay (Fig. 10; Thurber Consult- into small flakes or grains that move crystals produced in this manner form ants Limited 1983; Jackson et al. 1985). independently of one another. Snow a weak layer that changes only slowly All of the bridges and culverts along avalanches range in size from those too once buried. In contrast, the overlying Alberta Creek, with the exception of small to bury a person to more than and underlying snow layers commonly the British Columbia Railway bridge, one million m3, capable of destroying gain strength over a period of days to were destroyed. About 10 000 m3 of large buildings or many hectares of weeks, leaving the buried surface hoar debris were deposited below the high- forest. as a potential failure plane. Third, weak way; in addition, some sediment flowed layers of hoar can develop inside the into Howe Sound. Within the commu- Process snowpack. nity of Lions Bay, destructive tongues Slab avalanches, which are the most During the first few seconds of logs and boulders were forced out dangerous type, require a buried weak of a slab avalanche, the failed snow of the channel at corners and obstruc- layer and an overlying stronger mass of mass comprises large fractured blocks tions, one of which killed two people snow. Weather determines the evolu- of snow sliding downslope. The slab in a trailer. tion of the snowpack and the forma- rapidly gathers speed and, commonly Measures taken to protect tion of weak, unstable layers within the within a few tens of metres, disinte- people and property in Lions Bay and snow. The most important contributing grates into smaller fragments and, in elsewhere along Howe Sound from factors are heating by solar radiation, many cases, individual grains of snow. future debris flows include the con- radiative cooling, temperature gradients At velocities above about 35 km/hr, GEOSCIENCE CANADA Volume 37 Number 1 March 2010 27 dry avalanches commonly generate a cloud of powdered snow that billows above the main mass of flowing snow. Wet avalanches have higher densities than dry ones (300–400 kg/m3 vs. 50–150 kg/m3), but do not attain the extreme velocities of some large dry avalanches (Jamieson 2001). Large snow avalanches may have sufficient momentum to climb tens of metres or more up opposing slopes and destroy the forest cover. They may also dis- place air, producing a damaging air blast that arrives seconds before the avalanche. Most large snow avalanches are released from slopes with gradients of 30−45°, although some occur on slopes as steep as 60° (Abromelt et al. 2004). Slopes in the 30–45° range are Figure 11. Distribution of avalanche fatalities in Canada according to the activity also popular with skiers, snowboarders, of the victims at the time of the accident (Jamieson, 2001, p. 82). Categories and snowmobilers, which is why recre- include recreation (skiing, snowboarding, and snowmobiling); transportation, ationists often trigger avalanches. including highway and railway construction; resource industry, including accidents Fewer than 5% of dry snow avalanches at work camps; and residential and commercial buildings. Some accidents have been begin on slopes of less than 30°, but excluded because they do not fit any of these categories. In the past 50 years, the wet snow slides can occur on slopes number of recreational accidents has increased dramatically, whereas the number of under 25° (Abromelt et al. 2004). other accidents has decreased. Higher elevations commonly have a higher avalanche hazard than lower ones because they receive more snow, ational accidents has increased dramati- lion. This figure is conservative have fewer trees to impede avalanches, cally since the 1930s. Indeed, an aver- because it does not include railway and commonly are windier. Gullies or age of 12 people have died, annually, in delays or the effect of closures on ravines funnel snow avalanches, snow avalanches in Canada over the timely deliveries, lost business, and increasing their destructive force and past decade, and nearly all of them other indirect costs. making escape difficult. were recreationists who were buried in Property damage caused by an avalanche that either they or a snow avalanches in Canada in most Snow Avalanches in Canada member of their group triggered. years is less than $500 000, although Over 600 people have died in snow Snow avalanches also cause much damage is likely unreported. In avalanches in Canada since the earliest traffic delays, with significant economic comparison, damage from snow ava- reported accidents in the middle nine- losses (Morrall and Abdelwahab, 1992). lanches in the European Alps in some teenth century (Stethem et al. 2003; For example, closures of the Trans- winters can be an order of magnitude Abromelt et al. 2004). Until the early Canada Highway associated with snow larger than in Canada. Typical infra- twentieth century, most avalanche fatal- avalanches in Rogers Pass, BC, average structure damaged in Europe includes ities were people engaged in construc- about 100 hours per winter. A typical residential and commercial buildings in tion of railways and roads, or working two-hour closure of this highway can ski resorts, ski lifts, vehicles, and com- at mine sites (Fig. 11). The Canadian result in monetary losses of between munication and power lines. Snow ava- Pacific Railway line, completed in 1886, $50 000 and $90 000, depending on lanches also damage forests by uproot- was the first rail line built across Cana- the number of trucks that are delayed ing, breaking, and injuring trees. da. During construction of the rail line (Morrall and Abdelwahab 1992); the Most snow avalanches in and in the early years of its operation, average annual cost of snow avalanch- Canada occur in remote or uninhabited ‘white death’ snow avalanches claimed es at Rogers Pass alone due solely to areas during fall, winter, and spring, approximately 250 lives in Rogers Pass traffic delays is therefore several mil- and therefore go unnoticed. They are in Glacier National Park, British lion dollars. This sum does not include extraordinarily common – by one esti- Columbia (Woods 1983). The number the costs of preventing avalanches and mate, about 1.5 million snow avalanch- of industrial and transportation fatali- clearing the highway during closures. es large enough to bury a person occur ties from snow avalanches, however, is Taking into account the many other annually in western Canada (Jamieson now low, mostly because pre-emptive highways in British Columbia that are 2001). Yet, only about 100 avalanche measures to reduce the risk are rou- affected by snow avalanches, the total accidents are reported in this region tinely taken to protect road and rail annual cost of traffic delays in that each year. Most snow avalanches occur lines. In contrast, the number of recre- province alone likely exceeds $5 mil- in the mountains of Alberta, British 28

Columbia, Yukon, and Northwest Ter- ritories (Fig. 12). They are also com- mon in parts of Labrador, in the Gaspé region of Québec, along the north shore of the St. Lawrence River, in parts of Newfoundland, and along the eastern margin of the Arctic Islands. Snow avalanches are uncom- mon, except in localized areas, in the Prairies and Arctic, and in central and eastern Canada.

RIVER FLOODS Flooding can occur along any stream or river and, consequently, is the most universally experienced natural hazard. In Canada and the United States, floods have caused more damage than any other hazardous process in the twentieth century − some 10 000 peo- ple have been killed since 1900 and property damage has exceeded $4 bil- lion per year over the past decade alone (Andrews 1993). Most river flooding is related to the amount and distribution of pre- cipitation in the drainage basin, the rate at which the precipitation infiltrates the ground, the presence or absence of a snowpack, air temperature, and how quickly runoff reaches the river. Antecedent soil moisture conditions are also important because water-satu- Figure 12. Regional occurrence of snow avalanches in Canada. The map is gener- rated soil cannot hold additional mois- alized−among other things, it does not take into account isolated steep areas and ture; flooding is more likely if heavy isolated areas of heavy snowfall or strong winds. Modified from Jamieson (Fig. 12, rains fall on a saturated drainage basin 2001). or on frozen ground. Flooding can also result from the formation and subsequent break- peak discharge of a ‘normal’ rainfall or basins of these rivers are too large to up of ice jams on rivers, and from the snowmelt-triggered flood in the same be influenced by thunderstorms or by sudden draining of lakes impounded basin. Such floods and associated a single cyclonic storm. Mid-sized behind moraines, glaciers, and landslide debris flows can be deadly if people rivers may also crest during the late deposits (Fig. 13; Costa and Schuster live along their paths. For example, a spring, although those in temperate 1988; Clague and Evans 1994, 2000). debris-laden flood caused by the failure areas such as the Pacific coast com- Glacier dams are notoriously unstable of a moraine dam at Lago Placacocha monly flood in the fall during periods and can fail due to flotation of part of in the Cordillera Blanca of Peru in of heavy rain after snow has accumu- the dam or, alternatively, to drainage 1941 killed about 5000 people in the lated on the ground. Small streams can through tunnels at the base of the ice. city of Huaraz (Lliboutry et al. 1977). flood at any time of the year − during For example, Summit Lake in north- spring when snow rapidly melts or rain western British Columbia has drained Temporal and Geographic falls on still-frozen ground; in mid- rapidly via an ice tunnel at the base of Distribution water thaws; or during summer rain- Salmon Glacier nearly every year since Flooding occurs at different times of storms. These streams can reach flood 1961 (Fig. 14; Mathews 1965; Mathews the year in Canada depending on the stage very quickly. Ice-jam floods occur and Clague 1993). A moraine dam may geographic location of the watershed in most parts of Canada, but are espe- be rapidly incised by overtopping and the size of the stream or river cially common in the north. They hap- waves triggered by a landslide or ice involved. Large Canadian rivers, e.g. pen when rivers ice-over in the fall or avalanche into the lake. The sudden the Fraser and the Red, always flood in during ice break-up in late spring draining of water impounded in the late spring due to a combination of (Brooks et al. 2001). Ice cover along lake can produce a flood with a peak melt of heavy snowpacks, prolonged upstream reaches of a river may break discharge many times larger than the warm weather, and heavy rainfall. The up and then jam against downstream GEOSCIENCE CANADA Volume 37 Number 1 March 2010 29

Figure 14. Summit Lake, located in the northern Coast Mountains of British Columbia, is dammed by Salmon Gla- cier. Summit Lake drains once a year, typically over three or four days, through a 7-km-long ice tunnel at the base of the glacier. Although brief, the floods (lower right) have peak dis- charges much larger than those caused by snowmelt or rain- fall.

dikes and in relo- 1922, 1923, 1960, 1966, 1969, 1970, cating nearly 1974, 1979, 1984, 1986 (Andrews 1993; 25 000 evacuees Brooks et al. 2003), and 2009. Given along the Red this history, the Red River Floodway is River Valley. The being expanded, with an expected Figure 13. Oblique aerial view of the breached moraine at floodwaters inun- completion date in 2010, further reduc- Nostetuko Lake in the southern Coast Mountains of British dated the broad ing the flood risk to the city. Columbia. In 1983, an ice avalanche from the retreating toe valley floor to Geology plays an important of Cumberland Glacier (arrow) plunged into Nostetuko Lake, depths of 12 m role in Red River flooding in two ways. generating waves that overtopped and breached the moraine and created a vast First, the Laurentide Ice Sheet dam. The sudden release of 6 million m3 of water produced a temporary lake depressed the crust several hundred huge, though short-lived, flood in the valley below. Photo by some 40 km metres during the late Pleistocene. Stephen Evans, Geological Survey of Canada. across and 1840 Because the centre of ice loading was km2 in area (Fig. located to the north, the magnitude of 15). Many com- depression decreased progressively to river ice. River water rises against the munities were under water or cut off the south into the United States. As a downstream obstruction and spills out from surrounding areas; three people result, isostatic rebound has been, and of its channel, inundating the adjacent drowned; and damage totalled $815 continues to be, greater at the northern low-lying floodplains. Flooding may million (Brooks et al. 2001). Winnipeg end of the Red River Valley than in the also occur when the ice jam breaks, was spared because the Red River south; the gradient of the Red River is releasing the impounded water behind Floodway, constructed at considerable therefore decreasing, making it pro- the dam. cost after an earlier flood, channelled gressively more difficult for the river One of the areas in Canada at peak flows around the city (Fig. 16). channel to contain flood waters greatest risk of flooding is southern The floodway has been used in 27 of (Brooks et al. 2001). Second, most of Manitoba (Brooks et al. 2001, 2003). In the 40 years since its completion. In the Red River Valley is underlain by the spring of 1997, rapid snowmelt contrast, in the spring of 1951, a flood low-permeability clay deposited in gla- and heavy rain on water-saturated and similar to that of 1997 and resulting cial Lake Agassiz, a huge late Pleis- frozen soils produced widespread and from similar conditions, lasted 51 days, tocene lake impounded by the retreat- prolonged flooding along the Red forcing the evacuation of 60 000 peo- ing Laurentide Ice Sheet. River Valley in North Dakota, Min- ple in Manitoba; nearly 10 percent of Another notable Canadian nesota, and southern Manitoba. Over Winnipeg was inundated during this flood disaster was the Fraser River 7000 military personnel were mobilized event. Since 1900, other damaging Red flood in early June 1948. A late, but for 36 days to assist in strengthening River floods occurred in 1904, 1916, wet spring and the rapid onset of 30

Figure 15. Rural communities in southern Manitoba and North Dakota experienced their worst flooding in nearly 50 years in May 1997 when the Red River, swollen from melting snow, spilled over its banks and across the broad valley floor. Photo by Greg Brooks, Geological Survey of Canada. warm temperatures triggered rapid the watersheds in melting of a heavy snowpack in late the Toronto May (Sewell 1969). The river level rose region (Andrews and overtopped dikes in the Fraser 1993). The del- Lowland beginning on 26 May (Fig. uge caused the 17). Flood waters peaked on 10 June at most severe Figure 16. The Red River Floodway was built after the river Mission; by that time, the river had flooding in over flooded Winnipeg in 1951. The photograph shows the con- breached over a dozen dikes and flood- 200 years. trol structure at the south end of the city that diverts part of ed about 20 000 ha of land. Much of Because there the Red River flow into the Floodway. Photo by Greg Brooks, Agassiz and Rosedale, and parts of was considerable Geological Survey of Canada. Mission were inundated (Andrews urban develop- 1993). Vancouver was isolated from ment on most of the affected flood- percent of all hurricane-related fatali- the rest of Canada, except by air plains, flood damage was high, estimat- ties in the United States (Flanagan (Sewell 1969). Ten people died, 200 ed at over $150 million. More than 20 1993). A storm surge is a local rise in families were left homeless, and 16 000 bridges were destroyed, 81 lives were sea level that occurs when hurricane people were evacuated. Three thou- lost, and almost 1900 families were left winds drive seawater inland. Tropical sand buildings were destroyed and 82 homeless (Andrews 1993). cyclones commonly generate storm bridges were washed out. The total surges of over 3 m, and surges of 12 cost of the disaster is estimated to SEVERE WEATHER m or more have been recorded in have been $133 million (1991 dollars; Hurricanes Bangladesh and Australia (Burt 2004). Andrews 1993). Hurricanes are primarily a threat to the Higher storm surges develop on broad, Severe flooding can also Atlantic provinces, although, as men- shallow coastlines where the forward accompany hurricanes that reach Cana- tioned earlier, weakened hurricanes can motion of wind-driven water is imped- da. The worst flood disaster in Canadi- cause severe flooding in south-central ed by friction. Storm surge and wind an history occurred in October 1954, Canada. Damage and loss of life from damage in the Northern Hemisphere when Hurricane Hazel struck Toronto. hurricanes result from winds, storm are greatest in the right, forward quad- The hurricane produced record precip- surges, and flooding caused by heavy rant of the storm as it makes land- itation, with an estimated 210 mm of rainfall. Storm surges cause the great- fall−this is the direction the storm is rain falling over a 36-hour period on est damage and are responsible for 90 travelling and also rotating, thus the GEOSCIENCE CANADA Volume 37 Number 1 March 2010 31

Figure 17. View south across flooded farmland in the east- ern Fraser Lowland during the 1948 Fraser River flood. Source: Province of British Columbia. wind speed at the ground is higher ment Canada Figure 18. Satellite image of Hurricane Juan on September there than on the other side of the eye 2004b). 28, 2003, just before it made landfall near Halifax, Nova Sco- of the hurricane. The height of the The tia. Source: National Oceanographic and Atmospheric surge will also be greater if the hurri- most deadly tor- Administration. cane comes onto land at high tide. nado in Canadian Hurricane Juan (Fig. 18), which struck history occurred in central Alberta on blizzards’ rework existing snow to pro- Halifax with peak winds of about 160 the afternoon of July 31, 1987. The duce whiteout conditions with visibility km/hr on September 29, 2003, was a tornado, rated F4 on the Fujita scale, limited to a few metres or less. The harsh reminder that Atlantic Canada is ripped through Edmonton, killing 27 Saskatchewan blizzard of 1947 lasted vulnerable to tropical storms. It killed people and injuring 300 more; property for 10 days and buried an entire train eight people and caused more than damage amounted to $330 million. The in a 1-km-long snowdrift that was up $200 million in damage in Nova Scotia tornado remained on the ground for to 8 m deep (Environment Canada and Prince Edward Island, including almost an hour, achieving wind speeds 2004a). Another famous storm, the major damage to trees and property in of up to 460 km/hr and cutting a path ‘Blizzard of 1888,’ killed more than the urban core of Halifax. of destruction 40 km long and up to 1 400 people and paralyzed the north- km wide (Charlton et al. 1997). Other eastern United States for three days Tornadoes recent deadly tornadoes in Canada with snow drifts that reportedly cov- Tornadoes are much more common in include a F3 event that travelled across ered the first floors of many buildings. the midwestern United States and Pine Lake, Alberta, and into a trailer East coast blizzards commonly occur southern Canada than elsewhere in the park in July 2000 (11 people killed, 132 during ‘nor’easters’, which derive their world, largely because the flat, low injured); and a F4 tornado that struck name from continuously blowing topography of central North America Barrie, Ontario, in May 1985 (more northeasterly winds that precede the allows subtropical and arctic air masses than 800 people were left homeless, 8 storm. Nor’easters wreak havoc, with to interact. The southern and central people died, and 60 were seriously hurricane-force winds, heavy snowfall, United States, in particular, has just the injured). and high waves. right combination of weather, topogra- phy, and geographic location to make it Other Meteorological Hazards Hailstorms a perfect spawning ground for torna- Blizzards Large hailstones from severe thunder- does (Grazulis 2001). Most US and The official threshold for blizzard con- storms pose a hazard to property in Canadian tornadoes occur in spring ditions in Canada is winds in excess of parts of southern Canada. Starting and summer in the region extending 40 km/hr, with visibilities of less than with a small ice pellet as a nucleus, a from Florida to Texas and north to 1 km for at least four hours (Environ- hailstone attracts a coating of liquid southern Alberta, Saskatchewan, Mani- ment Canada 2002). A blizzard may water in the lower part of the storm toba, and Ontario (Fig. 19; Environ- also occur without snowfall−‘ground and that coating freezes when a strong 32

from drought in Canada, mainly to agriculture but also reduced hydroelec- tric power production, amount to more than $1 billion each year (Keller et al. 2008). Prolonged droughts, lasting many years, have taken particularly severe economic and personal tolls. Most of us are aware of the dry hot weather of the 1930s, when crops in the midwestern United States and southern Canada failed and thousands of farms were abandoned. However, climate reconstructions from the southern Canadian prairies, based on tree-ring evidence, show that there have been longer and more severe droughts in the past 500 years (St. George et al. 2009). Longer proxy records of climate on the prairies, derived from studies of lake sediments and their pollen and other fossils, have also revealed frequent periods of drought during the Holocene (Vance et al. 1993, 1997; Lemmen et al. 1997; 2 Figure 19. Average annual number of tornadoes per 10 000 km based on data Leavitt et al. 1999). from 1950 to 1998 (Eisen 2001). updraft carries the stone upward, back with colder objects, such as roads, Heat waves into cold air. This process is repeated trees, and utility lines. Much of the world is vulnerable to many times, forming a large nodule of The worst Canadian ice storm heat waves, which are periods of ice. The annual damage caused by hail of the last century occurred in January extreme heat that are both longer and in the United States and Canada aver- 1998 (Government of Québec 1999). hotter than normal. In recent years, ages over $1 billion (Burt 2004). In After five days of freezing rain, parts heat waves have killed an average of Canada, damaging hailstorms are most of Québec, Ontario, New Brunswick about 220 people per year in the Unit- common in the southern prairies, espe- and the northeastern United States ed States and Canada, which is about cially in Alberta. were crippled by up to 10 cm of accu- the same as total deaths from flooding, mulated ice, leading to the collapse of lightning, tornadoes, and hurricanes Ice storms steel power transmission towers, power combined (Keller et al. 2008). Most Ice storms occur when rain at a tem- poles, and trees. People throughout the summer heat waves in Canada are perature near 0°C instantly freezes as it affected region were without electricity, associated with high-pressure ridges. comes into contact with colder sur- water, and phone service, in some Conditions west of the ridge are gener- faces. They typically occur during the cases for weeks. More than 5 million ally wet, whereas sunny and dry weath- winter months on the north side of a people were affected by blackouts, and er prevails to the east. If the ridge stationary or warm front when three at least 35 people died, mostly in remains stationary for several days, air conditions are met: Québec, as a result of house fires, temperatures below the ridge may rise, 1. An ample source of moisture is falling ice, carbon monoxide poisoning, triggering a heat wave. The air can be present in the warm air mass south and hypothermia. either humid or extremely dry during of the front; heat waves; a combination of high 2. Warm air overlies a shallow layer Drought temperature and high humidity can of cold air; and Over one billion people live in semi- produce a humidex value (a measure of 3. Objects on the land surface are at arid regions of the world where the body’s perception of air tempera- or below freezing (Keller et al. droughts are common, and over 100 ture) in the high 40s (°C), which is 2008). million people are at risk of malnutri- extremely dangerous. Snow begins to fall from the tion or death if drought causes their colder, upper part of the warm air crops to fail (Keller et al. 2008). In COASTAL EROSION AND SEA-LEVEL mass and then melts as it passes Canada, southern Alberta and southern RISE through the warmer air below. The Saskatchewan, Canada’s most impor- Many towns and cities in Canada are resulting raindrops then become super- tant grain-producing region, are the located on, or near, coasts and are cooled as they pass through the near- most vulnerable parts of the country therefore vulnerable to sea-level rise surface cold air and freeze on contact to drought. Direct and indirect losses and erosion by waves. Fewer than 20 GEOSCIENCE CANADA Volume 37 Number 1 March 2010 33

000 people live on Canada’s Arctic during deglaciation. This process is continues to warm. Some scientists coast, so coastal hazards directly affect- augmenting the rise in global (eustatic) have suggested that hurricanes may ing people are much less of a problem sea level caused by melting of glaciers become more frequent and powerful there than elsewhere in the country. and thermal expansion of upper ocean later in this century as near-surface Demographic trends indicate that more waters, and is contributing to coastal waters in the Atlantic Ocean and than half of Canada’s population will erosion in some areas of Atlantic Caribbean Sea warm (Parry et al. eventually be concentrated along the Canada. In contrast, coastal areas 2007). In such cases, both the hazard Pacific and Atlantic sea coasts and around Hudson Bay and the Arctic and vulnerability increase, causing a along the shores of the Great Lakes. Islands are experiencing isostatic uplift much higher level of risk in some Shorelines in Canada that are due to late Pleistocene and early areas. most vulnerable to erosion are those Holocene deglaciation, which is offset- Climate warming poses other backed by Quaternary sediments ting eustatic sea-level rise (Andrews hazards to Canada. Sea-level rise and (Clague and Bornhold 1980; Clague 1970; Gough and Robinson 2000). stronger, more frequent storms could 1989; Shaw et al. 1998). Coastal areas Worldwide, sea level is rising inundate low-lying coastal areas and notable for such sediments include the at a rate of about 2 mm/yr. Scientists accelerate erosion of some shorelines. Strait of Georgia in British Columbia, predict that sea level will rise several Thaw of the permafrost in the Arctic parts of Graham Island in Haida tens of centimetres, and perhaps con- is a potentially serious problem for Gwaii, Lake Ontario, Lake Winnipeg, siderably more, over the remainder of Canadians living in the north because it and parts of Nova Scotia. Although this century (Parry et al. 2007). What- is accompanied by irregular settlement sea ice limits fetch and therefore ever the exact amount, coastal erosion of the ground and increases in thaw- reduces wave erosion (fetch length will become an even greater problem layer detachment failures. A related over open water combined with wind than it is today. Sea-level rise will also problem is accelerated erosion of ice- speed determines wave size) through- threaten low-lying coastal areas with rich coastlines bordering the Arctic out much of the central and northern inundation (Clague 1989). Areas at Ocean. Parts of the west may experi- Arctic, erosion rates of up to 2 m/yr greatest risk of inundation are delta ence more precipitation and more have been observed in the western plains, e.g. the Fraser River delta south intense rainfall, both of which are Arctic, e.g. along parts of the Beaufort of Vancouver, and coastal wetlands. important triggers of landslides. In Sea shoreline (Shaw et al. 1998). A Initially, inundation by the sea is likely contrast, much of southern Canada developing problem in the Arctic that to occur during severe cyclonic storms may experience more frequent and is not an issue elsewhere is thawing of that temporarily raise sea level, and at more severe droughts, accompanied by permafrost. The Arctic has warmed times of unusually high tides. The an increase in wildfires and reduced significantly over the past several Fraser River delta plain, on which near- agricultural output. decades. This warming, together with ly 300 000 people now live, is protect- Risk may also increase because wave erosion and sea-level rise, has ed from the sea by an extensive system of human activities and decisions. The eroded ice-rich coastal sediments and of dikes, but these structures will have continued development of the Fraser triggered active layer detachment fail- to be strengthened and raised if sea River floodplains east of Vancouver, ures. Some Inuit villages are threatened level continues to rise as expected. encroaching settlement of steep slopes by the erosion and may have to be in mountain valleys of western Canada, relocated at considerable cost. RISK IN THE TWENTY-FIRST and settlement of fire-prone areas at Erosion on the Atlantic coast CENTURY the urban–wildland interface are exam- is aggravated by hurricanes and other Risk from natural hazards is expected ples of trends that are increasing our severe storms, by sea-level rise, and by to increase in Canada through the exposure to natural hazards. Deforesta- human interference with natural shore remainder of this century. The fre- tion and overgrazing reduce or elimi- processes. Some shorelines in Atlantic quency of hazardous events caused by nate roots that stabilize the soil cover, Canada, where sea level is rising more internal Earth forces − earthquakes, increasingly the likelihood of land- rapidly than elsewhere in North Ameri- tsunami, and volcanic eruptions – slides, erosion, stream siltation, and ca, are retreating at rates of up to 10 probably will not change, but Canada’s flooding. m/yr (Forbes et al. 1989). Sea-level rise vulnerability to them will likely increase As we reflect on future trends in this region is due, in part, to contin- due to population growth and concen- in risk in Canada, it is important to uing crustal subsidence associated with tration of wealth in hazard-prone areas note two opposite historical trends at the disappearance of the Laurentide such as Vancouver. In effect, the haz- play in the developed world. First, the Ice Sheet. The ice sheet displaced vis- ard does not change, but vulnerability, costs associated with natural disasters cous material in the mantle away from and therefore risk, increase. have increased exponentially during the the centre of loading toward the This generalization may not past few decades (Fig. 1). Increased periphery, creating an uplifted bulge apply to landslides and to hydro-mete- concentrations of wealth in hazard- beneath Atlantic Canada. When the ice orological hazards, including severe prone urban areas, poor preparedness, sheet melted, the uplifted bulge col- storms, hailstorms, ice storms, floods, and lack of understanding and aware- lapsed and the land beneath Atlantic drought, and heat waves. The frequen- ness of hazards have contributed to Canada subsided. It continues to do so cy and magnitude of these processes this increase. Second, deaths and today, although at a slower rate than could change if, as expected, climate injuries from natural disasters in North 34

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