Belatedly just caught this thread for the first time today. Noticed there has been much specualtion about how steep various slopes are. And controversy of estimating such and such a slope is XX degrees and such. Well I have been measuring ski slope gradients for years so will share some information although the post will by necessity be a bit lengthy.
First let me state that individual estimates, ski resorts, ski writers, ski magazines, and others have been getting much of this wrong for years. harpo was correct in his assessment. Mostly because individuals want to use impressive figures when skiing difficult terrain the numbers go up. I've seen articles about say the "...ten steepest ski slopes..." etc which were published in major ski books of their day which apparently simply used figures given to them by some local authority. The list was useless. On the opther hand there has been some fairly accurate information like the 1975 "Mammoth" mountain guide book by Hiatt and Wright.
Two ways slope gradient measurement may be done without resorting to surveying equipment are:
Go to a hardware store and buy one of those cheap circular angle measuring fluid levels. They are used for measuring the angle of say boards for wood construction projects. With that can approximately estimate the angle of specific locations on a slope. Given the obvious simplicity, I won't go into the mechanical details on how to use such with modest accuracy and rather leave it to the user's ingenuity. The problem with this is one would need to make lots of measurements along a slope.
Slopes can be numerated in either degrees or percent grade. The latter is more useful although writers often mistakenly mix the two interchangeably which makes the result twice reality. Briefly percent grade is vertical height divided by horizontal distance in percent. A 45 degree slope is 100 percent grade.
The second method uses a topographic map essentially by measuring the distance between elevation lines and applying basic trigonometry.
Many years ago when planning a trip to ski Snowbird, I wanted some idea of the topography of the slopes, so I wouldn't end up in some overly scary spot. I mail ordered a topographic map from the USGS and a trail map from the resort. From that I was able to size up all the gradients, exposures, and ways to move around the mountain. A couple days after a foot plus of powder I was confronted by locals deep within Black Forest wondering how some totally new dude could be poaching their private spots.
Today one does not necessarily need to buy say a 7.5 degree USGS topographic map as that information is available on the www internet at either:http://terraserver.microsoft.comhttp://topozone.com
Basically you can get a topo map for anywhere in the USA. Also one can get ski resort trail maps at eitherwww.skimaps.com
or by going to say Yahoo and doing a search on the resort name. All resort web sites have trail maps.
Besides a topographic map and trail map one will also need an ordinary magnifying loupe, 6x or 8x would be fine, a ruler with one hundredths of an inch graticule divisions, and any scientific calculator (MS Window one will do) to do the trig conversion. The General brand 12 inch steel ruler can be found in many stationary stores.
In my example below I will use as an example one of the steepest long bump slopes in any US resort, West Face at Squaw Valley. When one measures such a slope they ought to make the measurement betwen the section of slope which is steep as many runs have lower gradient approaches and runouts. Also one needs to be able to figure out where on the topo, the actual run is. It may take some detective work but for me that is not usually much of a problem but others will no doubt be lost. Two individuals may get slightly different results because they measure a line on the same run in slightly different lines. I pencil a line on the map before I start.
For most 7.5 minute USGS topographic maps:
1 vertical line = 40 feet
1 dark vertical line every 5 lines = 200 feet
1 map mile at 40 degree latitude is about 2.63 inches
Each map has a scale, measure it.
40 feet horizontal distance on a map =
(2.63 * 40) / 5280 = 0.01992 inches
200 feet horizontal distance on a map =
(2.63 * 200) / 5280 = 0.09962 inches
Thus if the spacing between a set of dark lines (200 feet
vertical) are 0.099 inches on the map, then the slope is
100% grade or 45 degrees.
West Face at Squaw Valley
Now for those who have skied West Face and are disappointed with what may appear to be wimpy numbers, let me share a few others per the summary line.
8200' to 6680', vert 1520' 1.62" 46.7% 25 degrees
steepest 200 feet = 55%
Liftline at Stowe:
3640' to 1560, vert 2080' 5.105" 35.0% 19.3 degrees
steepest 200 feet = 52%
Exibition at Sun Valley:
7440' to 6400', vert 1040 49.1% 26.1 degrees
steepest 200 feet = 55%
Al's Run at Taos
11040' to 9440', vert 1600' 3.77" 52.7% 27.8 degrees
steepest 200 feet = 67.1%
Now for an example of a really steep well skied bump run, the top 450 feet of Climax at Mammoth Mtn is about 93% grade or over 40 degrees. And that brings up a minor issue. Runs which start at ridge lines may be steeper for short sections at the top from snow loading cornices. In Mammoth's case, the long Cornice has many nearly vertical drops for short distances. -dave