Many are the tales of successful escape from disaster by storm, made possible by reliance upon a so-called sense of direction, or upon the legend that moss always grows on the north side of trees. The skier, how­ever, should bear in mind that there are perhaps many more tales of failure to escape disaster which never have been told, and, indeed, never can be. Bearing this in mind, he should acquire an adequate knowledge of the proper use of compass and map, and rely on this knowl­edge—and not on superstition—when he is required to travel with visibility poor or in country that is new.

Magnetic declination.—The angle between the direc­tion in which the compass needle points and true geo­graphic north is known as the magnetic declination. The needle is aligned with the strongest lines of magnetic force affecting it. In the absence of such magnetized objects as a knife, ice ax, steel pole, or local beds of magnetic ore, the needle will always point approximately toward the north magnetic pole of the earth. This is on Boothia Peninsula, about 1300 miles south of the geo­graphic north pole. Consequently, at about Cincinnati, magnetic north and true north will be in line. East of Cincinnati the compass needle will point west of true north; west of Cincinnati it will point east. A clear understanding of this will show how declination varies, and why one cannot rely upon declination marked upon a compass, which may be made in France but used in British Columbia.

Fig. 9. Relation of magnetic north to true north (simplified).

Conversion of compass readings.—The amount and direction of declination is nearly always shown on better maps. To obtain a true map reading where there is an east declination, add the amount of the declination to the compass reading; in localities having west declina­tion, subtract the amount. In the field it is usually simplest to use magnetic bearings throughout, since no conversion is then necessary.

If the magnetic declination is not known, it can be determined as accurately as the compass will read by taking a bearing on Polaris, the North Star.

Determination of compass bearings.—A compass bear­ing is simply the angle between the direction of an object and that of magnetic or true north or south. By deter­mining on the map the bearings of several points of a chosen route, the skier may plot his course of travel. To facilitate accurate readings, north, east, south, and west should be marked on the compass case so that the pivot of the needle can be placed accurately over a particular point on the map. With the compass centered over the point on the map from which the bearing is to be taken, and with the map oriented, the bearing can be read directly from the compass by use of a line from the center of the compass to the object whose bearing is desired. The reading where the line crosses the divisions of the compass is the bearing.

Compasses are marked according to two major sys­tems. Easiest to use, and standard with the United States armed forces, is the azimuth system, by which bearings are specified in degrees up to a circle of 360°, in a direction clockwise from north. Compasses graduated on that system usually have the case marked counterclock­wise, so that if the north—south line of the case is directed toward the object, the north end of the needle will read directly in degrees of azimuth. Thus a north­west bearing would be given as 315°.

Most civilian surveying in the United States is based upon four segments of the circle, graduated respectively from north and south 90° in each direction to east and west; a northwest bearing is given as north 45° west.

Plotting of compass bearings.—This is merely the reverse of determining the bearings from a map. With a compass centered over the point on the map from which the bearing was taken, and with the map properly oriented, a line can be projected through the graduation on the compass which corresponds to the bearing. The point to which the bearing is taken will be on that line if the reading and plotting are accurate. If one is using his own bearings, it will be simpler to keep them all magnetic to avoid conversion errors.

Use of a compass in storm.—A storm provides the vital justification for carrying a compass at all times in ski mountaineering, for visibility in storm is greatly re­duced. One must rely upon the accuracy of the compass, taking care to eliminate local magnetic influence. If such influence is suspected, several readings on a distant object should be taken on a straight course at intervals of about 400 yards. If uniform, the readings will elimi­nate the possibility of local attraction. One's sense of direction may, under stress, sometimes be completely off—as much as 180°. To avoid this, mark the compass case to show which end of the needle is north.

A storm may require a party to retreat in poor visi­bility, so it may be well to record distances traveled in each direction as well as compass bearings of prominent landmarks along the route. Then, knowing the bearing, locate a landmark as far away as visibility will permit, and proceed toward that landmark for the distance re­quired. If the chosen landmark is likely to be obscured for any reason, an intermediate landmark should be chosen on the same line before the distant one is lost.

Visibility may be so poor that no landmarks are seen. The last man in the party should then direct the travel by compass, sighting ahead on the other two men and thus maintaining a straight line. In turning to pass such an obstacle as a cliff or open stream, one can return to the original line by carefully recording the new angle of direction and the distance traveled. Easiest to use is a series of right angles. A shorter but slightly less accurate method is to diverge from the original course at a diagonal to clear the obstacle, returning to the course by the same angle on the opposite side of the obstacle and with the same number of paces (see fig. 10).

Fig. 10. Two methods of maintaining a compass course around obstacles.

Orienting the map.—The compass is necessary if land­marks cannot be identified. Keeping the north—south line of the compass case parallel to any north-south grid on the map, rotate the map and compass until the north end of the compass needle coincides with the local declina­tion. All directions on the map will then coincide with those on the ground.

A map is most satisfactorily oriented by use of a known location on the map and a known landmark. Placing matches or pine needles vertically on the map at the location and landmark, rotate the map until the matches align with the known landmark. The map is thus oriented, more accurately than by compass.

A map may be oriented with three known landmarks, but with one's own location unknown. Place a match near the center of a thin sheet of paper and sight across it to another match which is lined up with one of the known landmarks. Draw a line on the paper in that direction. Without moving the paper, sight across the center match to the other landmarks and draw similar lines. The landmarks should be as diverse as possible. Placing this sheet over the unoriented map, move it to a position in which all three lines will, on the map, pass through the three known landmarks. The center point from which the lines were drawn will then be the position of the observer, and the map can be oriented with any one of the three landmarks.

A rough way to determine south and thus orient the map is by use of a watch and the sun. If the hour hand is pointed directly toward the sun, a line drawn halfway between the hour hand and 12 will point approximately south. This method, while not accurate, may be much better than nothing at all. Use local standard time.

Determining one's unknown position.—This is possibly the most valuable use of a map in emergency. Every ef­fort should of course be made to keep so well ac­quainted with the map and country that one's position will always be known. Nevertheless, prolonged travel under restricted visibility may bring one to a position which cannot be determined by simply glancing at the map. If landmarks shown on the map can be recognized in the distance, choose two whose direction is separated approximately by a right angle (for greater accuracy). Orient the map by compass, place a match vertically on the map above the position of one of the known land­marks, move another match along the near edge of the map until it aligns with the landmark, and draw a light line between the two vertical matches. Then repeat the process for the other known landmark.

Fig. 11. Method of determining intervisibility.

The intersection of the two lines thus obtained will be near your position. A more precise determination can then be made by sight­ing on additional known landmarks.

If a compass is not available, one's position can be determined by sighting three known landmarks.

To identify unknown landmarks reverse the procedure for identifying position. With only one line of sight, the exact position of the landmark can only be determined if one has enough knowledge of the country and of maps to know how distant the feature is, its shape, and its position with reference to intervening ridges.

Determining intervisibility.—Experience in reading top­ographic maps can usually show approximately whether any two points should be intervisible. This may be checked by a procedure such as follows:

Draw a dotted line between the observation station and the peak whose visibility is to be tested and determine their difference in elevation. Draw a line from the higher point at right angles to the dotted line, and, if the differ­ence in elevation is, for example, 500 feet, mark five equal divisions on the right-angle line. Checking along the dotted line, draw a second right-angle line to repre­sent the ridge that might obstruct the view. Using the same divisions as before, mark on this second line the difference in elevation between the station and the ridge. A line drawn from the "summits" of the right-angle lines representing the station and obstruction is then extended as far as the peak. If the peak line is high enough to rise above the extended line, the peak can then be seen from the observation station.

An easy variation is to substitute for the dotted line a rubber band upon which the equal divisions of the difference in altitude have been marked. By stretching the rubber band between the station and the peak, one can easily determine whether the elevation of any inter­vening obstruction is higher or lower than the elevation division marked on the rubber band at that point.

If a distance of more than a few miles exists between the station and the peak, allowance must be made for curvature of the earth and refraction of light by the atmosphere.

Contour topography.—The most accurate method of representing land forms upon a map is provided by contour topography, the method used throughout the United States in maps of the Geological Survey. On the back of most of these maps is an excellent diagram showing a landscape in relief drawing and in contour topography.

A contour is a line every point of which is at the same elevation. The shore line at mean low tide is the zero contour for all United States surveys and maps. If the coast has a ten-foot tide, the water will follow up each inlet and cross each beach to establish, in effect, a new contour line, ten feet higher. Ten feet would then be the contour interval. The interval between contours usually varies according to the scale of the map and roughness of the country, but is uniform throughout a particular map.

In land forms resulting from water erosion, contours along stream channels are normally V-shaped, the V pointing upstream; shoulders and ridges are usually U-shaped, the U pointing downhill. An understanding of the main drainage system will make it easier to under­stand the relation of ridges and minor valleys and gullies to the main canyons and mountain systems.

A contour line cannot end except on itself (or at the edge of the map). If it ends on itself, it will form a closed circuit which usually indicates a peak or ridge crest, the interior portion of the circuit being higher than any portion along its edges. Such contours may also show a depression. For that use, they are usually marked with short, right-angle lines inside the closed circuit. In desert regions, depressions may be on such a vast scale that such a method of marking is not practical. They may then be recognized by the form of the rest of the topog­raphy and a careful check to determine which contours are higher than others.

Contours are close together when the land surface is steep, far apart when it is gradual. A vertical cliff is indicated by many contours converging to form a single line. Contours cross only when they represent an over­hanging cliff. It is rare to find maps which are of such scale and accuracy that they will show the fine detail of an overhang.

Adequate knowledge of contour topography is dif­ficult to obtain from any manual. It is suggested that the skier first become familiar with the United States Geo­logical Survey map of his home locality or usual skiing area. Recommended for further study are: Yosemite Valley Special Sheet (for detail of cliff sculpture), Mount Rainer National Park (for glaciers), and the Wabuska or Carson Sink sheets of Nevada (for desert forms).

The map and the ski tour.—A skier makes good use of his ability to visualize terrain by reading a good topo­graphic map, correlating this information with his knowl­edge of the region and basic ski-mountaineering require­ments. The slope can be determined roughly by the spacing of the contours. The height of the slope can be told at a glance. The experienced map reader will recog­nize which slopes are so long and of such high angle that they will be especially subject to avalanches. The ex­posure of the slope, readily seen on the map, will suggest what will be the effect of sun upon the snow. The skier may thus be able to plan his trip on north slopes to take advantage of powder snow; in spring he may choose north slopes at certain times of day to take advantage of frozen crust, or south slopes to avoid it. Angle and direction of slope may determine wind exposure, to be avoided in storm, or sought on a hot day. The map will suggest where cornices are formed, and where wind-slab avalanches are most likely; it may tell, indirectly, where a timberline camp may be made, which slopes will be open, which heavily forested. The campsite can be chosen with regard to distance that the party will best travel in a day over the terrain as disclosed by study of the map. Choice of campsite may be affected by the availability of "liquid" water to save fuel in cooking. Sites near lakes and streams, which may be open in part, will be selected. The map may show which campsite should have reason­able protection against storm and freedom from the ava­lanche hazard which would exist at the base of long, high slopes or steep chutes.

Nor should the skier overlook the pure enjoyment a thorough knowledge of his maps can give him, either while he plans and anticipates his trip, or, after it is over, when he traces the trails over which his skis have taken him.

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