Big Four Ice Caves — Saturday, Mar. 6, 1999

North Cascades > Mountain Loop Highway

The trailway is well packed, mostly by snowshoers, and easy to follow. The snow load on the bridges is incredible. The main bridge over the South Fork Stilliguamish is piled six feet above the top of the handrails. That's almost 10 feet of snow along the entire length of the bridge! The bridge is nearly 100 feet long and about 4 feet wide, so the total volume of snow on the bridge is about 4000 cubic feet. This is equal to 6,912,000 cubic inches, but one gallon is equal to 231 cubic inches so that's 29,922 gallons. Now water weighs about 8.3554 lbs/gallon at 4°C under one atmosphere (760 mm Hg), but since this is snow and not water the density is some what less because of air pockets. If we estimate the density to be about .6321 of water, then that's a total of 158,031.5 pounds or 79 tons. That's equal to 29.85 Chevy Suburban LT 4x4s. Golly!