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<br />' 1.0 INTRODOCTION <br />On the evening of April 9, 1986 and throughout the following day <br />' (April 10, 1986), a series of landslides triggered by recent <br />rains developed immediately above the access road and portal area <br />for Bear Mine No. 3. It is our understanding from mine personnel <br />' that a two-week period of light rain preceded the slides on April <br />9. The rains intensified during the weeY, immediately prior to <br />' the slides and intensified even more the last two days prior to <br />the slide. Rains were of the steady, high infiltration, low <br />' runoff type and rates reportedly approached one inch of <br />' precipitation per day on the day immediately prior to the <br />sliding. Other factors affecting the development of the slide <br />' include a perception by long-term residents that the weather in <br />the valley has been in a "wet cycle" for the last three or so <br />f years with heavier than normal annual amounts of precipitation. <br />t Yet another factor is the fairly warm winter during 1985-1986. <br />During normal years, a layer of frost would still exist at depth <br />in early April on the north facing slopes to inhibit infiltration <br />and promote surface runoff. This year, there was no frost, <br />' allowing maximum infiltration during the steady rains. <br />' Two separate areas of sliding affected the operation of the mine. <br />The first involved the running of an existing debris flow chute <br />located in the area between the fan portal and the entry and belt <br />' portals. Small debris flow events commonly occur within this <br />' chute each year. This particular event, however, was larger than <br />most and deposited some estimated 3,600 cubic yards of mud and <br />' debris on the mine bench effectively cutting off vehicular access <br />1 <br />