Avalanche Fracture Line SNOW HYDROLOGY (GEOG 4321): HOMEWORK ASSIGNMENT 5

Instuctor: Mark Williams
Telephone: 492-8830


Homework 6

  1. Calculate the shear stress in N/m2 in a snowpack given the following parameters:
    1. density = 250 kg/m3; snow height = 1 meter; and slope angle = 30 degrees.
    2. Change the slope angle to 45 degrees. What is the shear stress? What is the precentage change in the shear stress caused by the increase in slope angle?
    3. Do the same calculation as in b, but increase snow density and snowpack depth: density = 450 kg/m3; snow height = 2.5 meter; and slope angle = 45 degrees. What is the shear stress? What is the precentage change in the shear stress caused by these changes compared to problems a and b?
  2. What is the maximum velocity and impact pressures of avalanches in the following situations?
    1. An open slope, slope angle of 35 degrees, flow depth of 2 meters, a flowing density of 150 kg/m3, mu = 0.3, and coefficient of turbulent friction of 750 m/s2.
    2. Same situation, but a rocky slope? note the coefficient of turbulent friction is 500 m/s2 for rocky slopes.
    3. An open slope, slope angle of 50 degrees, flow depth of 2 meters, a flow density of 500 kg/m3, and mu = 0.2.
  3. The local forecast states that a recent storm has deposited champagne powder at Niwot Ridge: 1 meter of new snow with a density of 80 kg/m3. You and a group of friends have decided to head out into the backcountry and put first tracks on a great bowl near Berthoud Pass, which has an angle of 40 degrees. Before leaving Boulder, the wind picks up and is blowing 20 m/s. Describe how you would use this information to decide which slopes to ski. Once you arrive at Berthoud Pass, what other steps might you take to evaluate the stability of the slope before skiing? One page maximum.
  4. Use the following information to construct a ram profile of snowpack hardness. This information was collected at Niwot Ridge on 980224. See pages 141-150 of the Avalanche Handbook. Calculate the Ram Hardness number in Newtons. Ram penetrometer equation and explanation. Remember, a Newton (kg-m/s2) is mass X acceleration, or kilograms X gravity (m/s2). 
    P	T	H	n	f
cm	kg	kg	number	cm
13	2	0	0	0
2	2	1	2	10
2	2	1	1	20
2	2	1	1	20
2	2	1	1	20
2	2	1	1	20
1	2	1	1	20
1	2	1	1	30
4	2	1	1	30
6	2	1	1	30
1	2	1	1	30
2	2	1	2	30
1	2	1	1	40
1	2	1	1	40
2	2	1	1	50
1	2	1	1	50
2	2	1	1	60
1	2	1	1	60
3	2	1	1	60
3	2	1	1	60
9	2	1	1	60
3	2	1	1	60
1	2	1	1	60
2	2	1	1	60
1	2	1	1	60
1	2	1	1	60
1	2	1	1	60
2	2	1	1	60
7	2	1	1	60
1	2	1	1	60
1	2	1	1	60
1	2	1	1	60
1	2	1	1	60
1	2	1	1	60
1	2	1	1	60
2	2	1	1	60
6	2	1	1	60
7	2	1	1	60
3	2	1	1	30
1	2	1	1	30
1	2	1	1	30
    This files reads from the top of the snowpack going down to the bottom. You need to calculate snow depth for each measurement using the first column. The x-axis should be R (snow hardness, in Newtons) and the y-axis snow depth, from the ground to the snow surface. Snow depth can be in either meters or cms; cms is easier to use since P and f are in centimeters.
  5. Using the following information, graphically compare the ram profile above with the following pit information collected at the same site on the same date: density, temperature, and stratigraphy. Place all info on the same graph, with the y-axis snow height above the ground. How well does the ram profile compare to these other parameters in evaluating the snowpack stability? If this snowpack was placed on a 40 degree slope, would it be likely to slide? Why? 
    DENSITY and TEMPERATURE
top	bottom temp	density
layer	layer	degC	kg/m3
111	111	-5	NA
111	100	-6	190
100	90	-7	280
90	80	-8	320
80	70	-8	390
70	60	-8	356
60	50	-8	375
50	40	-7	355
40	30	-7	355
30	20	-6	310
20	10	-5	290
10	0	-4.5	280
0	0	-4	NA


    STRATIGRAPHY
top	bottom	grain	size
layer	layer	type	microns
111	60	ET	0.5
60	43	ET	1.0
43	33	CR	NA
33	15	ET	1.5
15	0	TG 	3.0

ET is equitemperature snow grains
TG is temperature gradient snow grains
CR is a buried crust