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Lab 2. General Quantitative Methods in Geology (2)

1. Contour lines (lines of equal values; in geology they show elevations)

Help to visualize terrain; base for making topographic profiles.

Provide a base for measurements of slope (gradient)

Show patterns

Can be drawn not only for elevations but also for mapping physical

measurements such as temperatures, pressures, depth, or

concentration of ores.

2. Topographic Profiles (based on contour lines)

Show how terrain changes along a specific direction. Useful for

building roads, measuring slopes, etc.

Show shapes of landforms, e.g. volcanoes, valleys

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Drawing Contour Lines:

Interpolation is a way to find unknown values from known within their min and max values.

Example: on a map below, min and max values are 0 and 50. Therefore, if we draw contour lines

with 10-foot interval, they will consist of five contour lines 0, 10, 20, 30 and 40.

Two main rules of interpolation:

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Notice in map A that a 500-foot contour line has been drawn through all the points that have an

elevation of 500 feet above mean sea level. This is not interpolation but just connection of points

with the same elevation. On map A we see that minimum value is 482 and maximum value is 515.

Therefore we can interpolate between these values.

Practice and finish contouring both maps using a contour interval of 10 feet, i.e. make contour lines

with values 490, 500, 510.

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Topographic Profiles:

Select two points (A – A`) and draw a line of topographic profile

Place the edge of the paper strip along profile and mark contours

Place the edge of the paper strip along graph paper boundary, make

vertical elevation scale, mark elevation values as dots and connect

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Problem Sets:

I. Contour Lines.

Create contour lines from elevation points on map B using 10 foot interval:

Before you start, answer these useful questions:

What is min elevation: ________

What is max elevation: ________

How many 10 foot contour lines can you make: ___________

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II. Creating contour lines by interpolation for data other than elevation:

The map above shows an outline of a drainage basin or watershed. The data points

represent locations of rain gage stations. The numbers show the total 24-hour rainfall

amounts (inches) for each station. Draw an isohyetal contour map (contour map with lines

connecting points of equal rainfall) using a contour interval of 1 in (i.e. draw contour lines

for the following isohyets: 1.0, 2.0, 3.0, 4.0, 5.0. Remember to follow the rules of contour

and to interpolate the lines between data points as necessary.

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III. Making Topographic Profiles. Use graph paper to make a topographic

profile A’ - A.

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