What is Strike?
The strike is the compass direction of a line marking the intersection of an inclined plane with a horizontal plane such as the Earth’s surface.
Measuring Strike
In order to measure the strike, place the side or edge of the compass against the plane of the outcrop. Sometimes it is easier to put your field book against the outcrop and then the compass against the book to get a smoother and/or larger surface. Now, rotate the compass keeping the lower side edge of the compass fixed, until the bulls-eye level bubble is centered (the round tube; not the long narrow one). When the bubble is centered, the compass is horizontal against the plane and parallel to the line of strike. Now, with the bulls-eye bubble centered, record the number that either end of the compass needle is showing.
What is Dip?
The dip is the maximum angle between the inclined plane and the horizontal plane. The dip is always perpendicular to strike and has both a compass direction and an angle.
Measuring Dip
Measuring Dip using Brunton compass
To measure the dip of the bedding plane, take your Brunton compass and put its side against the rock so that it points in the same direction as the line of dip (The dip line is perpendicular to the strike line). Move the clinometer until the clinometer level bubble is centered. As, we did when we found the strike, record where the white-tipped end of the clinometer needle is pointing. Note the degrees and the direction. Recall that the dip direction MUST always be perpendicular to the strike direction (e.g., a strike of 40° could only dip to the SE or NW, never NE or SW).
How to use Brunton compass to measure bearing?
What is Bearing?
A bearing is a measurement of direction between two points. Bearings are generally given in one of two formats, an azimuth bearing or a quadrant bearing.
AZIMUTH BEARING
An azimuth bearing uses all 360° of a compass to indicate direction. The compass is numbered clockwise with north as 0°, east 90°, south 180°, and west 270°. So a bearing of 42° would be northeast and a bearing of 200° would be southwest, and so on.
QUADRANT BEARING
For quadrant bearings the compass is divided into four sections, each containing 90°. The two quadrants in the northern half of the compass are numbered from 0° to 90° away from the north (clockwise in the east, counterclockwise in the west). In the southern half of the compass, the two quadrants are numbered away from the south (counterclockwise in the east, clockwise in the west).
Quadrant bearings are given in the format of N 40°E (northeast), S 26°W (southwest), etc. Whenever you measure a quadrant bearing, it should always be recorded with north or south listed first, followed by the number of degrees away from north or south, and the direction (east or west) away from north or south. In other words, you would never give a quadrant bearing as E 40°N or W 24°S.Brunton Compass-How to use it for measure Bearing?
The first thing you need to do is determine the bearing from point A to point B. There are two ways to go about this.
The easiest way is to carry a protractor with you when you’re in the field. If you have a protractor with you, place it on the map so it is oriented parallel to a north-south gridline, with the center of the protractor on point A (or on a line drawn between points A and B). Once you have done this, you can simply read the bearing you need to go off of the protractor.If you don’t happen to have a protractor with you, you can determine the bearing you need using your compass. To do this, place your compass on the map so that the edge of your compass is oriented parallel to a north-south gridline and the center of your compass is on the line between points A and B.
Now rotate the map and compass together until the north arrow on the compass points to 0° on the graduated circle. You can then approximate the bearing you need by estimating where the line between A and B crosses the graduated circle.
MEASURING STRIKE AND DIP
Measuring strike:
To measure strike using the Brunton compass, geologists embark on a step-by-step journey that unfolds the secrets of rock layer orientation. As they navigate through the process, the compass becomes more than a tool; it’s a conduit that bridges geological observations with numerical precision.
Orient the compass with the bedding plane: Imagine standing before a rock outcrop, where layers of time are exposed like the pages of an ancient manuscript. The first step is to place the compass on the bedding plane, aligning its long axis with the direction of the layers. Just as an astronomer gazes at the stars, geologists peer at the rock layers, connecting with the Earth’s history.
Take the magnetic bearing: Just as a traveler consults a compass for direction, geologists use the Brunton compass to determine the magnetic bearing of the bedding plane. The compass needle aligns with the Earth’s magnetic field, indicating the magnetic north. This alignment becomes the geologist’s compass rose, guiding them in their measurements.
Rotate the compass to align the needle with the north direction: Like a conductor aligning musicians, geologists delicately rotate the compass until the needle aligns with the north direction on the azimuth scale. This alignment, akin to synchronizing the movements of a dance troupe, ensures accurate readings.
Read off the strike from the compass housing: With the compass poised, the magnetic bearing noted, and the needle aligned, geologists turn their attention to the compass housing. It’s here that the azimuth angle—the strike—is read. This number, etched in degrees, is the key that unlocks the Earth’s orientation, providing insights into geological processes that shaped the landscape.
Measuring Dip:
To measure the dip of the bedding plane, take your compass and put its side against the rock so that it points in the same direction as the line of dip (The dip line is perpendicular to the strike line). Move the clinometer until the clinometer level bubble is centered. As we did when we found the strike, record where the white tipped end of the clinometer needle is pointing. Note the degrees and the direction. Recall that the dip direction MUST always be perpendicular to the strike direction (e.g., a strike of 40° could only dip to the SE or NW, never NE or SW)
AFTER you determine strike, rotate the compass 90°.
Place the SIDE of the compass flat against the plane.
Adjust the lever on the back of the compass until the air bubble in the “Clinometer level” is centered.
Read the dip directly from the scale in the compass.
To measure dip using the clinometer on the Brunton compass is to embark on a journey that bridges observation and precision. The process is a dance between geologist and compass, where angles and inclinations reveal Earth’s hidden truths.
Align the compass vertically with the bedding plane: Imagine standing before a rock outcrop, where layers of time are exposed like the pages of a journal. The first step is to hold the compass against the rock, vertically aligning it with the layers’ inclination. Just as a reader peruses a story’s pages, geologists peer at the rock’s structure, preparing to decipher its plot.
Take the magnetic bearing: Similar to a traveler orienting themselves, geologists determine the magnetic bearing of the rock layers. The compass needle aligns with the magnetic north, a guide in the realm of angles. This alignment, a silent dialogue between Earth’s magnetism and the compass’s needle, sets the stage for the dip measurement.
Read off the dip angle from the clinometer scale: As a musician follows sheet music, geologists follow the compass’s clinometer scale. Holding the compass steady, they read the angle—the dip—from the clinometer. This number, etched in degrees, unlocks the layers’ hidden story, unveiling the Earth’s ancient movements with numerical precision.
In the symphony of geological exploration, measuring dip using the Brunton compass is a movement that harmonizes observation and calculation. It’s an interaction between geologist and Earth’s layers—a conversation that uncovers the layers’ inclinations, as if listening to whispers of the past. This measurement, captured in degrees and angles, is more than just a number; it’s the chronicle of Earth’s geological dynamics. As geologists align the compass, take the bearing, and read the clinometer, they’re not just observers; they’re interpreters of Earth’s hidden language. Amidst angles and inclinations, the dip measurement emerges as a revelation—a thread connecting geological past and present, stitching together the very fabric of Earth’s structure.
Measuring Trend:
The “Fold-out pointer” should point down-plunge.
Hold the compass horizontally ABOVE the plane (the bubble in the “Bull’s eye level” should be centered).
Look directly down through the “Slot” in the “Fold-out pointer”.
Rotate the compass, keeping it horizontal, until the slot is parallel with the line to be measured. (the line should run straight down the middle of the slot).
Read the North end of the compass needle to obtain the value of trend.
Measuring Plunge:
Place the bottom EDGE of the compass flat on the line (the edge should be parallel to the line).
Make sure the compass is vertical.
Adjust the lever on the back of the compass until the air bubble in the “Clinometer level” is centered.
Read the plunge directly from the scale in the compass (the same way you read dip).