Measuring Strike and Dip with a Brunton
Link to sites with illustrations on the use of a Brunton for taking strike and dip
Department of Geology - Hartwick College This site offers a overview of taking a strike and dip on an outcrop surface, however, illustrations of the procedure are limited.
Department of Geology - University of Calgary This site utilizes a detailed sequence of photographs to illustrate the determination of strike and dip on an outcrop surface.
- Direct Contact Method -- Medium to High Dips
- Select a bedding or foliation surface that is relatively smooth. Check with your pocket magnet to make sure the rock is nonmagnetic. Place your field notebook on the surface to provide
a "smoothed" surface. Holding the Brunton in a horizontal orientation, use one of the bottom edges of the Brunton as a "straightedge" and place that edge on the surface of the notebook. Rotated the body of the Brunton until the bulls-eye level is cente
red. For the quadrant -type compass read the bearing in the northern quadrants (NE or NW). To measure dip use the Brunton as a clinometer. Place the base of the Brunton (the side opposite the level) on the notebook and rotate the body of the Brunton un
til you obtain the maximum vertical angle. Remember you must also note the direction of dip (e.g. N45°E 35°NW).
- Direct Contact Method -- Low Dips
- For surfaces with low dips (less than 15°) it is not possible to use the method describe above. The metal ring that protects the clinometer arm on the back of the Brunton prevents you from holding the edge of the Brunton against a gently dipping sur
face. To measure the strike in this situation, set the clinometer at 0° and place the Brunton on the inclined surface until the bubble of clinometer level is centered. You now have a horizontal line (a strike line), note the orientation (or draw a line
on your notebook or the outcrop) and record the strike. Dips can be measured in the same manner as more steeply dipping surfaces.
- Indirect Method -- Using a Single Outcrop
- It may not be possible to directly measure the strike and dip of a surface (e.g. it may be located on the opposite side of a stream), however, you can measure strike and dip by an indire
ct approach. (1) Orient yourself until your horizontal line-of-sight is parallel to the surface you wish to measure. In this orientation you are looking "edge-on" and should not be able to see the lateral extension of the surface, your line-of-sight is n
ow parallel to the strike direction. Measure the bearing of this orientation. To measure dip of the surface, maintain the orientation you used to measure strike, hold the Brunton at arms length, with the compass body facing you, rotate the body until t
he edge of the Brunton parallels the dipping surface, use the clinometer to measure the inclination, which is equal to dip. In the illustration below, the red line represents the trace of a bedding surface.
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