107-468: Burke Canyon is the canyon of the Burke-Canyon Creek, which runs through the northernmost part of Shoshone County , Idaho , U.S., within the northeastern Silver Valley . A hotbed for mining in the late-nineteenth and twentieth centuries, Burke Canyon now contains several ghost towns and remnants of former communities along Idaho State Highway 4 , which runs northeast through the narrow canyon to
214-479: A brutal response in 1892 and in 1899. Burke Canyon was the site of several natural disasters as well. Two major avalanches struck the canyon in the twentieth century: one on February 4, 1890, which killed three; and another in February 1910, which buried and killed twenty-five people. In the days after the February 1910 avalanche, snow and rock continued to dislodge from the canyon walls, inflicting additional damage on
321-424: A critical temperature gradient. Large, angular snow crystals are indicators of weak snow, because such crystals have fewer bonds per unit volume than small, rounded crystals that pack tightly together. Consolidated snow is less likely to slough than loose powdery layers or wet isothermal snow; however, consolidated snow is a necessary condition for the occurrence of slab avalanches , and persistent instabilities within
428-541: A drag force that was proportional to the square of the speed of its flow: He and others subsequently derived other formulae that take other factors into account, with the Voellmy-Salm-Gubler and the Perla-Cheng-McClung models becoming most widely used as simple tools to model flowing (as opposed to powder snow) avalanches. Since the 1990s many more sophisticated models have been developed. In Europe much of
535-533: A family was $ 44,685. Males had a median income of $ 38,315 versus $ 25,273 for females. The per capita income for the county was $ 19,020. About 13.8% of families and 17.9% of the population were below the poverty line , including 22.5% of those under age 18 and 8.3% of those age 65 or over. Shoshone County was historically a Democratic-leaning county, but has in recent years consistently voted for Republican presidential candidates, while favoring Democratic candidates locally and statewide. School districts include: It
642-463: A fracture at the bottom called the stauchwall. The crown and flank fractures are vertical walls in the snow delineating the snow that was entrained in the avalanche from the snow that remained on the slope. Slabs can vary in thickness from a few centimetres to three metres. Slab avalanches account for around 90% of avalanche-related fatalities. The largest avalanches form turbulent suspension currents known as powder snow avalanches or mixed avalanches,
749-450: A kind of gravity current . These consist of a powder cloud, which overlies a dense avalanche. They can form from any type of snow or initiation mechanism, but usually occur with fresh dry powder. They can exceed speeds of 300 km/h (190 mph), and masses of 1,000,000 tons; their flows can travel long distances along flat valley bottoms and even uphill for short distances. In contrast to powder snow avalanches, wet snow avalanches are
856-596: A long term, lasting from days to years. Experts interpret the recorded data and are able to recognize upcoming ruptures in order to initiate appropriate measures. Such systems (e.g. the monitoring of the Weissmies glacier in Switzerland ) can recognize events several days in advance. Modern radar technology enables the monitoring of large areas and the localization of avalanches at any weather condition, by day and by night. Complex alarm systems are able to detect avalanches within
963-411: A low velocity suspension of snow and water, with the flow confined to the track surface (McClung, 1999, p. 108). The low speed of travel is due to the friction between the sliding surface of the track and the water saturated flow. Despite the low speed of travel (≈10–40 km/h), wet snow avalanches are capable of generating powerful destructive forces, due to the large mass and density. The body of
1070-840: A narrow gulch , roughly 300 feet (90 m) across, with steep cliffs and hills on both sides. The hillsides of the canyon are so steep that the community of Burke only receives around 3 hours of full sunlight during winters. Burke Canyon experiences a continental climate , marked by warm summers and cold, snowy winters. In 2002, it was reported that around 300 people lived in or near the canyon. There are numerous communities and former communities located along Burke-Canyon Road in Burke Canyon, though several are now ghost towns . The communities include: Decades' worth of mining activity resulted in various metals leaching into Canyon Creek, contaminating much of Burke Canyon. Leftover waste rock from mines leached cadmium , lead , arsenic , and zinc into
1177-400: A number of methods including hand-tossed charges, helicopter-dropped bombs, Gazex concussion lines, and ballistic projectiles launched by air cannons and artillery. Passive preventive systems such as snow fences and light walls can be used to direct the placement of snow. Snow builds up around the fence, especially the side that faces the prevailing winds . Downwind of the fence, snow build-up
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#17328581292171284-413: A persistent weakness in the snowpack. When a slab lying on top of a persistent weakness is loaded by a force greater than the strength of the slab and persistent weak layer, the persistent weak layer can fail and generate an avalanche. Any wind stronger than a light breeze can contribute to a rapid accumulation of snow on sheltered slopes downwind. Wind slabs form quickly and, if present, weaker snow below
1391-400: A point significantly above the freezing point of water, may cause avalanche formation at any time of year. Persistent cold temperatures can either prevent new snow from stabilizing or destabilize the existing snowpack. Cold air temperatures on the snow surface produce a temperature gradient in the snow, because the ground temperature at the base of the snowpack is usually around 0 °C, and
1498-412: A point with only a small amount of snow moving initially; this is typical of wet snow avalanches or avalanches in dry unconsolidated snow. However, if the snow has sintered into a stiff slab overlying a weak layer, then fractures can propagate very rapidly, so that a large volume of snow, possibly thousands of cubic metres, can start moving almost simultaneously. A snowpack will fail when the load exceeds
1605-495: A reason for discontinuing the line. By 1939, the rail to Burke had been officially closed, and the tracks dismantled. By the late twentieth century, mining operations in Burke Canyon had slowed considerably. The Hecla Mine in Burke officially ceased operations on June 30, 1983, due to low metal prices. The last mine in Burke officially closed in 1991, and the town and several of the surrounding communities became ghost towns . Around 2010,
1712-592: A short time in order to close (e.g. roads and rails) or evacuate (e.g. construction sites) endangered areas. An example of such a system is installed on the only access road of Zermatt in Switzerland. Two radars monitor the slope of a mountain above the road. The system automatically closes the road by activating several barriers and traffic lights within seconds such that no people are harmed. Avalanche accidents are broadly differentiated into 2 categories: accidents in recreational settings, and accidents in residential, industrial, and transportation settings. This distinction
1819-417: A start zone where the avalanche originates, a track along which the avalanche flows, and a runout zone where the avalanche comes to rest. The debris deposit is the accumulated mass of the avalanched snow once it has come to rest in the run-out zone. For the image at left, many small avalanches form in this avalanche path every year, but most of these avalanches do not run the full vertical or horizontal length of
1926-623: A stock of dynamite in the Frisco Mill, causing the four-story mill to explode and kill six people. The violence soon spilled over into the community of Gem. From there, union miners who had successfully shut down both the Frisco and the Gem mines travelled west, to the Bunker Hill mining complex near Wardner , and closed down that facility as well. The Idaho National Guard and federal troops were dispatched to
2033-415: A storm. Daytime exposure to sunlight will rapidly destabilize the upper layers of the snowpack if the sunlight is strong enough to melt the snow, thereby reducing its hardness. During clear nights, the snowpack can re-freeze when ambient air temperatures fall below freezing, through the process of long-wave radiative cooling, or both. Radiative heat loss occurs when the night air is significantly cooler than
2140-472: A strike in 1892. After several died in a shooting war provoked by discovery of a company spy , the U.S. Army forced an end to the strike. Hostilities erupted once again in 1899 when, in response to the company firing seventeen men for joining the union , the miners dynamited the Bunker Hill & Sullivan mill . Again, people died, and the U.S. Army intervened, requested by Governor Frank Steunenberg , as
2247-412: A sufficient quantity of airborne snow, this portion of the avalanche can become separated from the bulk of the avalanche and travel a greater distance as a powder snow avalanche. Scientific studies using radar , following the 1999 Galtür avalanche disaster , confirmed the hypothesis that a saltation layer forms between the surface and the airborne components of an avalanche, which can also separate from
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#17328581292172354-626: A suspended sentence. The small Austrian village of Galtür was hit by the Galtür avalanche in 1999. The village was thought to be in a safe zone but the avalanche was exceptionally large and flowed into the village. Thirty-one people died. On 1 December 2000, the Glory Bowl Avalanche formed on Mt. Glory which is located within the Teton Mountain Range in Wyoming, United States. Joel Roof
2461-705: A three-month period throughout the Alps in Austria, France, Switzerland, Italy and Germany. This series of avalanches killed around 265 people and was termed the Winter of Terror . A mountain climbing camp on Lenin Peak, in what is now Kyrgyzstan, was wiped out in 1990 when an earthquake triggered a large avalanche that overran the camp. Forty-three climbers were killed. In 1993, the Bayburt Üzengili avalanche killed 60 individuals in Üzengili in
2568-617: A total of thirty occupied homes discharging untreated waste into the creek. In 2007, the DEQ sequestered $ 220,000 in order to help residents install new septic systems to prevent further contamination. In 2016, the EPA announced its plan to construct a waste repository in lower Burke Canyon in order to alleviate waste accumulation in Wallace. Some residents of the canyon objected to the repository, citing further pollution from diesel trucks used to transport waste in
2675-413: A variety of factors such as the snow's shear strength (which is itself dependent upon crystal form) and the configuration of layers and inter-layer interfaces. The snowpack on slopes with sunny exposures is strongly influenced by sunshine . Diurnal cycles of thawing and refreezing can stabilize the snowpack by promoting settlement. Strong freeze-thaw cycles result in the formation of surface crusts during
2782-403: Is a rigid fence-like structure ( snow fence ) and may be constructed of steel , wood or pre-stressed concrete . They usually have gaps between the beams and are built perpendicular to the slope, with reinforcing beams on the downhill side. Rigid barriers are often considered unsightly, especially when many rows must be built. They are also expensive and vulnerable to damage from falling rocks in
2889-562: Is called the Starting Point and typically occurs on a 30–45 degree slope. The body of the pathway is called the Track of the avalanche and usually occurs on a 20–30 degree slope. When the avalanche loses its momentum and eventually stops it reaches the Runout Zone. This usually occurs when the slope has reached a steepness that is less than 20 degrees. These degrees are not consistently true due to
2996-424: Is critically sensitive to small variations within the narrow range of meteorological conditions that allow for the accumulation of snow into a snowpack. Among the critical factors controlling snowpack evolution are: heating by the sun, radiational cooling , vertical temperature gradients in standing snow, snowfall amounts, and snow types. Generally, mild winter weather will promote the settlement and stabilization of
3103-408: Is flat enough to hold snow but steep enough to ski has the potential to generate an avalanche, regardless of the angle. The snowpack is composed of ground-parallel layers that accumulate over the winter. Each layer contains ice grains that are representative of the distinct meteorological conditions during which the snow formed and was deposited. Once deposited, a snow layer continues to evolve under
3210-435: Is in the catchment area, but not the taxation zone, for North Idaho College . Avalanche An avalanche is a rapid flow of snow down a slope , such as a hill or mountain. Avalanches can be triggered spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, other animals, and earthquakes . Primarily composed of flowing snow and air, large avalanches have
3317-470: Is lessened. This is caused by the loss of snow at the fence that would have been deposited and the pickup of the snow that is already there by the wind, which was depleted of snow at the fence. When there is a sufficient density of trees , they can greatly reduce the strength of avalanches. They hold snow in place and when there is an avalanche, the impact of the snow against the trees slows it down. Trees can either be planted or they can be conserved, such as in
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3424-504: Is motivated by the observed difference in the causes of avalanche accidents in the two settings. In the recreational setting most accidents are caused by the people involved in the avalanche. In a 1996 study, Jamieson et al. (pages 7–20) found that 83% of all avalanches in the recreational setting were caused by those who were involved in the accident . In contrast, all the accidents in the residential, industrial, and transportation settings were due to spontaneous natural avalanches. Because of
3531-402: Is sufficiently unsettled and cold enough for precipitated snow to accumulate into a seasonal snowpack. Continentality , through its potentiating influence on the meteorological extremes experienced by snowpacks, is an important factor in the evolution of instabilities, and consequential occurrence of avalanches faster stabilization of the snowpack after storm cycles. The evolution of the snowpack
3638-523: The Hecla Mining Company has been exploring the potential of exploiting additional resource deposits in the Star mine. As of December 2012, Hecla invested $ 7 million in rehabilitation and exploration with published estimates suggesting the potential to recover in excess of 25 million ounces of silver from the site with significant zinc and lead deposits also present. The structure of Burke Canyon resembles
3745-732: The Idaho National Guard troops were still stationed in the Philippines following the Spanish–American War . Steunenberg was assassinated outside his residence in Caldwell in 1905, nearly five years after leaving office, and the subsequent trials in Boise in 1907 made national headlines. Much of the county was burned in the Great Fire of 1910 , including parts of Wallace . According to
3852-598: The Montana border. Burke Canyon takes its name from the town of Burke ; settlers arrived in the canyon in 1884 after silver , lead , and zinc were found in mines throughout. Between 1886 and 1890, numerous mining communities developed in the canyon. Many of the communities in Burke Canyon saw multiple labor disputes, namely the Coeur d'Alene labor strike of 1892 and the confrontation of 1899 , which resulted in violent conflict between miners and mine owners. Populations throughout
3959-580: The Native American Shoshone tribe. Shoshone County is commonly referred to as the Silver Valley , due to its century-old mining history. The Silver Valley is famous nationwide for the vast amounts of silver , lead , and zinc mined from it. Shoshone County was formed under the Territory of Washington on January 9, 1861. The territorial legislature established the county in anticipation of
4066-667: The Rogers Pass avalanche in British Columbia , Canada. During World War I , an estimated 40,000 to 80,000 soldiers died as a result of avalanches during the mountain campaign in the Alps at the Austrian-Italian front, many of which were caused by artillery fire. Some 10,000 men, from both sides, died in avalanches in December 1916. In the northern hemisphere winter of 1950–1951 approximately 649 avalanches were recorded in
4173-510: The U.S. Census Bureau , the county has an area of 2,635 square miles (6,820 km ), of which 2,630 square miles (6,800 km ) is land and 5.5 square miles (14 km ) (0.2%) is water. As of the census of 2000, there were 13,771 people, 5,906 households, and 3,856 families living in the county. The population density was 5 people per square mile (1.9 people/km ). There were 7,057 housing units at an average density of 3 units per square mile (1.2 units/km ). The racial makeup of
4280-525: The United States Environmental Protection Agency (EPA) moved forward with plans to dispose of leftover rock piles and contaminated soil in Burke Canyon. Various metals also impacted the local water supply of Burke Canyon: After the closure of the last mine in Burke in 1991, residents' water supplies continued to be sourced from pipes that extended into abandoned mine shafts. Consequently, the metal content of Burke's water supply
4387-496: The angle of repose , depends on a variety of factors, such as crystal form and moisture content. Some forms of drier and colder snow will only stick to shallower slopes, while wet and warm snow can bond to very steep surfaces. In coastal mountains, such as the Cordillera del Paine region of Patagonia , deep snowpacks collect on vertical and even overhanging rock faces. The slope angle that can allow moving snow to accelerate depends on
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4494-488: The avalanche dam on Mount Stephen in Kicking Horse Pass , have been constructed to protect people and property by redirecting the flow of avalanches. Deep debris deposits from avalanches will collect in catchments at the terminus of a run out, such as gullies and river beds. Slopes flatter than 25 degrees or steeper than 60 degrees typically have a lower incidence of avalanches. Human-triggered avalanches have
4601-457: The Coeur d'Alene Mountains and was home to seven dividend-paying mines: the Gem of the Mountains, Frisco, Mammoth, Standard, Hecla, Tiger-Poorman and Hercules mines. On July 10, 1892, miners called a strike which developed into a shooting war between union miners and company guards . The first shots fired were exchanged at the Frisco mine in the early morning hours of July 11. The gunfire ignited
4708-502: The Khumbu Icefall), triggering a movement of broken ice chunks. The resulting movement is more analogous to a rockfall or a landslide than a snow avalanche. They are typically very difficult to predict and almost impossible to mitigate. As an avalanche moves down a slope it follows a certain pathway that is dependent on the slope's degree of steepness and the volume of snow/ice involved in the mass movement . The origin of an avalanche
4815-508: The SAMOS-AT avalanche simulation software and the RAMMS software. Preventative measures are employed in areas where avalanches pose a significant threat to people, such as ski resorts , mountain towns, roads, and railways. There are several ways to prevent avalanches and lessen their power and develop preventative measures to reduce the likelihood and size of avalanches by disrupting the structure of
4922-580: The Tiger Mine in Burke Canyon. The Tiger Mine was sold to S.S. Glidden for $ 35,000. In 1887, Glidden began construction on a three-foot-wide railway to transport hardrock ore out of the Tiger Mine. Meanwhile, a buildup of 100,000 pounds (45,000 kg) of ore had accumulated from the various mines in the canyon, leading to the establishment of the Canyon Creek Railroad, which had its first shipment to Wallace on December 12, 1887. The establishment of
5029-466: The United States. In 2001 it was reported that globally an average of 150 people die each year from avalanches. Three of the deadliest recorded avalanches have killed over a thousand people each. Doug Fesler and Jill Fredston developed a conceptual model of the three primary elements of avalanches: terrain, weather, and snowpack. Terrain describes the places where avalanches occur, weather describes
5136-406: The age of 18 living with them, 48.5% were married couples living together, 8.7% had a female householder with no husband present, 37.4% were non-families, and 31.3% of all households were made up of individuals. The average household size was 2.25 and the average family size was 2.79. The median age was 46.2 years. The median income for a household in the county was $ 36,654 and the median income for
5243-428: The age of 18 living with them, 52.70% were married couples living together, 8.10% had a female householder with no husband present, and 34.70% were non-families. 29.40% of all households were made up of individuals, and 13.60% had someone living alone who was 65 years of age or older. The average household size was 2.30 and the average family size was 2.82. In the county, the population was spread out, with 22.90% under
5350-467: The age of 18, 6.70% from 18 to 24, 25.50% from 25 to 44, 27.40% from 45 to 64, and 17.40% who were 65 years of age or older. The median age was 42 years. For every 100 females there were 99.40 males. For every 100 females age 18 and over, there were 97.00 males. The median income for a household in the county was $ 28,535, and the median income for a family was $ 35,694. Males had a median income of $ 30,439 versus $ 18,831 for females. The per capita income for
5457-408: The ambient air temperature can be much colder. When a temperature gradient greater than 10 °C change per vertical meter of snow is sustained for more than a day, angular crystals called depth hoar or facets begin forming in the snowpack because of rapid moisture transport along the temperature gradient. These angular crystals, which bond poorly to one another and the surrounding snow, often become
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#17328581292175564-455: The area. The incident marked the first violent confrontation between the workers of the mines and their owners. Hostilities would erupt at the Bunker Hill facility once again in 1899. In both disputes, issues included pay, hours of work, the right of miners to belong to the union, and the mine owners' use of informants and undercover agents . Violence committed by union miners was answered with
5671-426: The avalanche's path to slow it down. Finally, along transportation corridors, large shelters, called snow sheds , can be built directly in the slide path of an avalanche to protect traffic from avalanches. Warning systems can detect avalanches which develop slowly, such as ice avalanches caused by icefalls from glaciers. Interferometric radars, high-resolution cameras, or motion sensors can monitor instable areas over
5778-401: The building of a ski resort, to reduce the strength of avalanches. In turn, socio-environmental changes can influence the occurrence of damaging avalanches: some studies linking changes in land-use/land-cover patterns and the evolution of snow avalanche damage in mid latitude mountains show the importance of the role played by vegetation cover, that is at the root of the increase of damage when
5885-432: The bulk of the avalanche. Driving an avalanche is the component of the avalanche's weight parallel to the slope; as the avalanche progresses any unstable snow in its path will tend to become incorporated, so increasing the overall weight. This force will increase as the steepness of the slope increases, and diminish as the slope flattens. Resisting this are a number of components that are thought to interact with each other:
5992-458: The canyon's towns dwindled in the late-twentieth century after a series of natural disasters and mine closures, and the last active mine in the canyon was closed in 1991, leaving the majority of the communities unpopulated. The Environment Protection Agency includes Burke Canyon as part of the Coeur d'Alene basin's Superfund sites due to hard metal and waste contamination of Burke-Canyon Creek. Gold
6099-410: The canyon. 47°30′49″N 115°51′17″W / 47.51361°N 115.85472°W / 47.51361; -115.85472 Shoshone County, Idaho Shoshone County shə- SHOHN is a county in the U.S. state of Idaho . As of the 2020 census , the population was 13,169. The county seat is Wallace and the largest city is Kellogg . The county was established in 1864, named for
6206-435: The capability to capture and move ice, rocks, and trees. Avalanches occur in two general forms, or combinations thereof: slab avalanches made of tightly packed snow, triggered by a collapse of an underlying weak snow layer, and loose snow avalanches made of looser snow. After being set off, avalanches usually accelerate rapidly and grow in mass and volume as they capture more snow. If an avalanche moves fast enough, some of
6313-506: The county was $ 15,934. About 12.40% of families and 16.40% of the population were below the poverty line , including 21.80% of those under age 18 and 10.00% of those age 65 or over. As of the 2010 United States Census , there were 12,765 people, 5,605 households, and 3,511 families living in the county. The population density was 4.9 inhabitants per square mile (1.9/km ). There were 7,061 housing units at an average density of 2.7 units per square mile (1.0 units/km ). The racial makeup of
6420-427: The county was 95.4% white, 1.4% American Indian, 0.4% Asian, 0.2% black or African American, 0.1% Pacific islander, 0.5% from other races, and 2.0% from two or more races. Those of Hispanic or Latino origin made up 3.0% of the population. In terms of ancestry, 32.2% were German , 17.6% were Irish , 13.5% were English , 6.4% were Norwegian , and 4.4% were American . Of the 5,605 households, 25.4% had children under
6527-431: The county was 95.84% White , 0.11% Black or African American , 1.52% Native American , 0.23% Asian , 0.07% Pacific Islander , 0.49% from other races , and 1.74% from two or more races. 1.93% of the population were Hispanic or Latino of any race. 22.1% were of German , 14.0% American , 11.3% English , 9.7% Irish and 5.9% Norwegian ancestry. There were 5,906 households, out of which 26.70% had children under
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#17328581292176634-457: The county's 276 residents were located at Pierce and Orofino. In the 1870 national census, 65% of the population were Chinese. Until 1904, Shoshone County included present-day Clearwater County to the south. That portion was annexed by Nez Perce County for several years and then was established as a new county in 1911. When the Silver Valley population rose dramatically in the 1880s, the seat
6741-463: The creekbed. Ecologists found that long stretches of Canyon Creek were entirely uninhabited by fish due to the high levels of metal content in the water. Canyon Creek is considered one of the Coeur d'Alene basin's Superfund sites . The metals leached in Canyon Creek were partially responsible for the contamination of the Coeur d'Alene River, the most heavy-metal contaminated river in the world. In 2010,
6848-409: The depths, crystal forms, and layering of the seasonal snowpack. Slab avalanches are formed frequently in snow that has been deposited, or redeposited by wind. They have the characteristic appearance of a block (slab) of snow cut out from its surroundings by fractures. Elements of slab avalanches include a crown fracture at the top of the start zone, flank fractures on the sides of the start zones, and
6955-672: The difference in the causes of avalanche accidents, and the activities pursued in the two settings, avalanche and disaster management professionals have developed two related preparedness, rescue, and recovery strategies for each of the settings. Two avalanches occurred in March 1910 in the Cascade and Selkirk Mountain ranges; on 1 March the Wellington avalanche killed 96 in Washington state , United States. Three days later 62 railroad workers were killed in
7062-519: The early 20th century, notably the work of Professor Lagotala in preparation for the 1924 Winter Olympics in Chamonix . His method was developed by A. Voellmy and popularised following the publication in 1955 of his Ueber die Zerstoerungskraft von Lawinen (On the Destructive Force of Avalanches). Voellmy used a simple empirical formula, treating an avalanche as a sliding block of snow moving with
7169-532: The fact that each avalanche is unique depending on the stability of the snowpack that it was derived from as well as the environmental or human influences that triggered the mass movement. People caught in avalanches can die from suffocation , trauma, or hypothermia . From "1950–1951 to 2020–2021" there were 1,169 people who died in avalanches in the United States. For the 11-year period ending April 2006, 445 people died in avalanches throughout North America. On average, 28 people die in avalanches every winter in
7276-452: The flow of a wet snow avalanche can plough through soft snow, and can scour boulders, earth, trees, and other vegetation; leaving exposed and often scored ground in the avalanche track. Wet snow avalanches can be initiated from either loose snow releases, or slab releases, and only occur in snowpacks that are water saturated and isothermally equilibrated to the melting point of water. The isothermal characteristic of wet snow avalanches has led to
7383-460: The friction between the avalanche and the surface beneath; friction between the air and snow within the fluid; fluid-dynamic drag at the leading edge of the avalanche; shear resistance between the avalanche and the air through which it is passing, and shear resistance between the fragments within the avalanche itself. An avalanche will continue to accelerate until the resistance exceeds the forward force. Attempts to model avalanche behaviour date from
7490-485: The geographic reality, the county seat was at Pierce. Growth at Pierce was so rapid that Shoshone County boasted the largest vote of any county within Washington Territory at the territorial election of July 8, 1861. In less than a year, Shoshone County contained additional settlements at Lewiston , Elk City , Newsome, and Florence . On December 20, 1861, Nez Perce and Idaho counties were created from most of
7597-521: The gold rush that occurred after the discovery of gold at Pierce in October 1860. Their location of the northern boundary at a line drawn due east from the mouth of the Clearwater River , unknowingly placed the emerging mining settlement at Pierce outside of the county's boundaries while residents of the new Mormon settlement at Franklin were unknowingly within the established boundaries. Regardless of
7704-470: The greatest incidence when the snow's angle of repose is between 35 and 45 degrees; the critical angle, the angle at which human-triggered avalanches are most frequent, is 38 degrees. When the incidence of human triggered avalanches is normalized by the rates of recreational use, however, hazard increases uniformly with slope angle, and no significant difference in hazard for a given exposure direction can be found. The rule of thumb is: A slope that
7811-866: The ground surface beneath the snowpack influences the stability of the snowpack, either being a source of strength or weakness. Avalanches are unlikely to form in very thick forests, but boulders and sparsely distributed vegetation can create weak areas deep within the snowpack through the formation of strong temperature gradients. Full-depth avalanches (avalanches that sweep a slope virtually clean of snow cover) are more common on slopes with smooth ground, such as grass or rock slabs. Generally speaking, avalanches follow drainages down-slope, frequently sharing drainage features with summertime watersheds. At and below tree line , avalanche paths through drainages are well defined by vegetation boundaries called trim lines , which occur where avalanches have removed trees and prevented regrowth of large vegetation. Engineered drainages, such as
7918-508: The influence of the meteorological conditions that prevail after deposition. For an avalanche to occur, it is necessary that a snowpack have a weak layer (or instability) below a slab of cohesive snow. In practice the formal mechanical and structural factors related to snowpack instability are not directly observable outside of laboratories, thus the more easily observed properties of the snow layers (e.g. penetration resistance, grain size, grain type, temperature) are used as index measurements of
8025-413: The likelihood of an avalanche. Observation and experience has shown that newly fallen snow requires time to bond with the snow layers beneath it, especially if the new snow falls during very cold and dry conditions. If ambient air temperatures are cold enough, shallow snow above or around boulders, plants, and other discontinuities in the slope, weakens from rapid crystal growth that occurs in the presence of
8132-450: The local humidity, water vapour flux, temperature and heat flux. The top of the snowpack is also extensively influenced by incoming radiation and the local air flow. One of the aims of avalanche research is to develop and validate computer models that can describe the evolution of the seasonal snowpack over time. A complicating factor is the complex interaction of terrain and weather, which causes significant spatial and temporal variability of
8239-526: The mechanical properties of the snow (e.g. tensile strength , friction coefficients, shear strength , and ductile strength ). This results in two principal sources of uncertainty in determining snowpack stability based on snow structure: First, both the factors influencing snow stability and the specific characteristics of the snowpack vary widely within small areas and time scales, resulting in significant difficulty extrapolating point observations of snow layers across different scales of space and time. Second,
8346-421: The meteorological conditions that create the snowpack, and snowpack describes the structural characteristics of snow that make avalanche formation possible. Avalanche formation requires a slope shallow enough for snow to accumulate but steep enough for the snow to accelerate once set in motion by the combination of mechanical failure (of the snowpack) and gravity. The angle of the slope that can hold snow, called
8453-414: The new snow has insufficient time to bond to underlying snow layers. Rain has a similar effect. In the short term, rain causes instability because, like a heavy snowfall, it imposes an additional load on the snowpack and once rainwater seeps down through the snow, acts as a lubricant, reducing the natural friction between snow layers that holds the snowpack together. Most avalanches happen during or soon after
8560-427: The night and of unstable surface snow during the day. Slopes in the lee of a ridge or of another wind obstacle accumulate more snow and are more likely to include pockets of deep snow, wind slabs , and cornices , all of which, when disturbed, may result in avalanche formation. Conversely, the snowpack on a windward slope is often much shallower than on a lee slope. Avalanches and avalanche paths share common elements:
8667-475: The original territory of Shoshone County. On the following day, Shoshone's boundaries were shifted northward, containing most of present-day Clearwater County and a portion of present-day Shoshone County. This new boundary alignment left the existing settlement at Pierce and the new settlement of Orofino as the county's only settlements. The county's population dwindled as prospectors abandoned Pierce for gold prospects at Elk City and Florence. Idaho Territory
8774-407: The path. The frequency with which avalanches form in a given area is known as the return period . The start zone of an avalanche must be steep enough to allow snow to accelerate once set in motion, additionally convex slopes are less stable than concave slopes because of the disparity between the tensile strength of snow layers and their compressive strength . The composition and structure of
8881-414: The prevention of development in these areas. To mitigate the effect of avalanches the construction of artificial barriers can be very effective in reducing avalanche damage. There are several types: One kind of barrier ( snow net ) uses a net strung between poles that are anchored by guy wires in addition to their foundations. These barriers are similar to those used for rockslides . Another type of barrier
8988-550: The protective forest is deforested (because of demographic growth, intensive grazing and industrial or legal causes), and at the root of the decrease of damage because of the transformation of a traditional land-management system based on overexploitation into a system based on land marginalization and reforestation, something that has happened mainly since the mid-20th century in mountain environments of developed countries. In many areas, regular avalanche tracks can be identified and precautions can be taken to minimize damage, such as
9095-455: The province of Bayburt , Turkey . A large avalanche in Montroc, France , in 1999, 300,000 cubic metres of snow slid on a 30° slope, achieving a speed in the region of 100 km/h (62 mph). It killed 12 people in their chalets under 100,000 tons of snow, 5 meters (16 feet) deep. The mayor of Chamonix was convicted of second-degree murder for not evacuating the area, but received
9202-421: The railroad coincided with that of the town of Burke , from which the canyon takes its name. Burke was the largest mining community in the canyon, with a peak population of 1,400 in 1910. The community of Gem, just south of Burke, had been established in 1886. Both Gem and Burke attracted various miners as well as a large number of Swedish immigrants. By 1903, Burke Canyon was the most developed mining region in
9309-767: The recent work was carried out as part of the SATSIE (Avalanche Studies and Model Validation in Europe) research project supported by the European Commission which produced the leading-edge MN2L model, now in use with the Service Restauration des Terrains en Montagne (Mountain Rescue Service) in France, and D2FRAM (Dynamical Two-Flow-Regime Avalanche Model), which was still undergoing validation as of 2007. Other known models are
9416-409: The relationship between readily observable snowpack characteristics and the snowpack's critical mechanical properties has not been completely developed. While the deterministic relationship between snowpack characteristics and snowpack stability is still a matter of ongoing scientific study, there is a growing empirical understanding of the snow composition and deposition characteristics that influence
9523-453: The secondary term of isothermal slides found in the literature (for example in Daffern, 1999, p. 93). At temperate latitudes wet snow avalanches are frequently associated with climatic avalanche cycles at the end of the winter season, when there is significant daytime warming. An ice avalanche occurs when a large piece of ice, such as from a serac or calving glacier, falls onto ice (such as
9630-416: The slab may not have time to adjust to the new load. Even on a clear day, wind can quickly load a slope with snow by blowing snow from one place to another. Top-loading occurs when wind deposits snow from the top of a slope; cross-loading occurs when wind deposits snow parallel to the slope. When a wind blows over the top of a mountain, the leeward, or downwind, side of the mountain experiences top-loading, from
9737-413: The snow may mix with the air, forming a powder snow avalanche . Though they appear to share similarities, avalanches are distinct from slush flows , mudslides , rock slides , and serac collapses. They are also different from large scale movements of ice . Avalanches can happen in any mountain range that has an enduring snowpack. They are most frequent in winter or spring, but may occur at any time of
9844-429: The snowpack can hide below well-consolidated surface layers. Uncertainty associated with the empirical understanding of the factors influencing snow stability leads most professional avalanche workers to recommend conservative use of avalanche terrain relative to current snowpack instability. Avalanches only occur in a standing snowpack. Typically winter seasons at high latitudes, high altitudes, or both have weather that
9951-423: The snowpack, and the heat stored in the snow is re-radiated into the atmosphere. When a slab avalanche forms, the slab disintegrates into increasingly smaller fragments as the snow travels downhill. If the fragments become small enough the outer layer of the avalanche, called a saltation layer, takes on the characteristics of a fluid . When sufficiently fine particles are present they can become airborne and, given
10058-460: The snowpack, such as melting due to solar radiation, is the second-largest cause of natural avalanches. Other natural causes include rain, earthquakes, rockfall, and icefall. Artificial triggers of avalanches include skiers, snowmobiles, and controlled explosive work. Contrary to popular belief, avalanches are not triggered by loud sound; the pressure from sound is orders of magnitude too small to trigger an avalanche. Avalanche initiation can start at
10165-479: The snowpack, while passive measures reinforce and stabilize the snowpack in situ . The simplest active measure is repeatedly traveling on a snowpack as snow accumulates; this can be by means of boot-packing, ski-cutting, or machine grooming . Explosives are used extensively to prevent avalanches, by triggering smaller avalanches that break down instabilities in the snowpack, and removing overburden that can result in larger avalanches. Explosive charges are delivered by
10272-402: The snowpack; conversely, very cold, windy, or hot weather will weaken the snowpack. At temperatures close to the freezing point of water, or during times of moderate solar radiation, a gentle freeze-thaw cycle will take place. The melting and refreezing of water in the snow strengthens the snowpack during the freezing phase and weakens it during the thawing phase. A rapid rise in temperature, to
10379-401: The strength. The load is straightforward; it is the weight of the snow. However, the strength of the snowpack is much more difficult to determine and is extremely heterogeneous. It varies in detail with properties of the snow grains, size, density, morphology, temperature, water content; and the properties of the bonds between the grains. These properties may all metamorphose in time according to
10486-421: The top to the bottom of that lee slope. When the wind blows across a ridge that leads up the mountain, the leeward side of the ridge is subject to cross-loading. Cross-loaded wind-slabs are usually difficult to identify visually. Snowstorms and rainstorms are important contributors to avalanche danger. Heavy snowfall will cause instability in the existing snowpack, both because of the additional weight and because
10593-516: The towns of Burke and Mace, and causing numerous deaths. In August of that year, the Great Fire of 1910 would cause further damage to the communities in the canyon. Three years later, in May 1913, the communities were stricken by heavy rains that resulted in significant floods. The Northern Pacific railroad considered discontinuing service through the canyon after the depot was damaged in a July 1923 fire. The railroad also cited increased automobile traffic as
10700-449: The warmer months. In addition to industrially manufactured barriers, landscaped barriers, called avalanche dams stop or deflect avalanches with their weight and strength. These barriers are made out of concrete, rocks, or earth. They are usually placed right above the structure, road, or railway that they are trying to protect, although they can also be used to channel avalanches into other barriers. Occasionally, earth mounds are placed in
10807-483: The year. In mountainous areas, avalanches are among the most serious natural hazards to life and property, so great efforts are made in avalanche control . There are many classification systems for the different forms of avalanches. Avalanches can be described by their size, destructive potential, initiation mechanism, composition, and dynamics . Most avalanches occur spontaneously during storms under increased load due to snowfall and/or erosion . Metamorphic changes in
10914-458: Was created in 1863 and the first census of the territory in that year enumerated only 574 residents in Shoshone County. The county boundaries were expanded to include the Silver Valley by the legislative assembly of Idaho Territory when it officially created Shoshone County on February 4, 1864. The expanded territory contained no population at the second census of Idaho Territory in 1864. All of
11021-474: Was emptied via pipelines directly into Canyon Creek from the residences in Burke Canyon. By the turn of the twenty-first century, citizens of Burke had continued to dump up to 6,000 US gallons (23,000 L) of raw sewage into Canyon Creek per day. In 2004, the Panhandle Health District (PHD) and Idaho Department of Environmental Equality (DEQ) tested homes in Burke to identify contaminations, finding
11128-527: Was fifty times above that of federal water quality standards. In 2001, the EPA offered to buy out residents of Burke Canyon, citing water contamination in Canyon Creek, but residents refused. The following year, the EPA ordered the town of Burke to comply with the Safe Drinking Water Act ; however, given the small number of homes within the boundaries of the town, it would have cost each household an estimated $ 48,000 per year. For decades, raw sewage
11235-489: Was initially discovered in the early 1860s in the mountains to the north of the Snake River basin, which gave way to a large influx of prospectors. Silver , copper , and other minerals were subsequently discovered. Idaho experienced boom after boom, and mining towns arose overnight, boomed, and then disappeared as the miners left for the latest rush. In 1884, miners discovered significant amounts of silver, zinc , and lead at
11342-530: Was moved to Murray in 1884 (and to Wallace in 1898) to better serve the majority of the county's population. The southern area's population increased with homesteading in the Weippe area in the late 1890s. The vast distance and time required for travel to Wallace from the Clearwater River area prompted the southern portion to move to Nez Perce County. Hard rock miners in Shoshone County protested wage cuts with
11449-457: Was snowboarding recreationally in this backcountry, bowl-shaped run and triggered the avalanche. He was carried nearly 2,000 feet to the base of the mountain and was not successfully rescued. On 28 January 2003, the Tatra Mountains avalanche swept away nine out of a thirteen-member group heading to the summit of Rysy in the Tatra Mountains . The participants of the trip were students from
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