Field Methods Exam 1

relationship between width of an outcrop and true thickness

if beds are vertical or horizontal, width of outcrop = true thickness

how to measure strike angle of inclined beds

1. ?

3 scenarios to find true thickness

1. if v>h, t = cos(theta)-hsin(theta)

2. if h>v and top of syncline, t = hsin(theta)+vcos(theta)

3. if h>v and bottom of syncline, t = hsin(theta)-vcos(theta)

Topographic maps

map that utilizes contour lines to show topographic features

Contour lines

- lines of equal elevation on a topographic map

- separates point of higher elevation

- always close to form an irregular circle

Index Contour Lines

- darker, labelled contour lines

- usually every 5th contour line

Contour Interval

elevation difference between any two contour lines

Latitude

angular distance from earth equator, measuring north and south

Longtiude

angular distance from earths' prime meridian, measuring east and west

Graphic scale

line visually representing scale of the map

Ratio scale

numerical representation of the scale of the map; unitless

7.5 minute quadrangles

- area covering 7.5 minutes of latitude and longitude (7.5x7.5)

- detailed areas of large topographic maps

15 minute quadrangles

- area covering 15 minutes of latitude and longitude (15x15)

- detailed areas of large topographic maps

North arrows

- series of arrows, indicating magnetic north and true north

- magnetic north arrow is drawn off of true north arrow

Magnetic Declination

angle between true and magnetic north

Hill representation on a topographic map

concentric series of closed contours

Depression representation on a topographic map

concentric series of closed contours with hachures on the contours

Direction of river flow representation on a topographic map

flows opposite direction from the way the contours bend, "v"

Vertical Exaggeration

- shows relief of the surface of the profile against what it actually looks like in nature

- Vertical scale/Horizontal scale

Stratigraphy

- study and interpretation of stratified rocks, primarily sedimentary rocks

- entails identification, description, vertical/horizontal relations, mapping and spatial correlation

Stratigraphic column features

- heading

- scale

- lithologic column showing lithology with symbols and erosion

- description of beds

- legend

Sedlog column features

- grain size on bottom of column

- width of column = length of bed

- symbols for rock type and sedimentary structures are found in individual beds

- legend

What does measuring a stratigraphic column tell us?

- thickness of each unit

- spatial relationship to adjoining rock units

- differentiating and describing each layered unit in a rock sequence

Horizontal Plane

plane tangent to a gravitational equipotential surface

Vertical Plane

plane perpendicular to horizontal plane

Horizontal Line

line formed by intersection of a horizontal plane w/ another non horizontal plane

Vertical Line

line of intersection of two, nonparallel, vertical planes

Reference Bearing Line

- horizontal line from observer to a specific reference point

- defined as 0

Bearing

- angle between two vertical planes, one through the observer and reference point, other through observer and target point

Great Circle

- circle formed by intersection of the outer surface of a sphere and a plane passing through the center of the sphere

Longitudinal great circle

great circles that pass through both rotational poles

Magnetic north pole

located where N end of magnetic dipole axis intersects earth's surface

Magnetic declination

angle between longitudinal great circle passing through observer and magnetic N pole

Types of map scales

1. Equality of lengths statement

2. ratio

3. scale bar

Equality of lengths to equivalent ratio

- convert both lengths to same length unit

ex: 1 mm = 8 m

1 m = 1000 mm

1 mm = 8000 mm

1:8000

Scale bar to equivalent ratio

- measure length of scale bar

- convert scale bar reading to unit used to measure length of scale bar

- divide by length of scale bar

ex: length of scale bar: 15.5 mm

scale bar reading: 1 km

15.5 mm = 10^6 mm

1 mm = 645,161.3 mm

1:645,161.3