Lab 2:Topographic Maps, Outcrop Patterns, and Structure Contours
Lab 2:Topographic Maps, Outcrop Patterns, and Structure Contours
Lab 2:Topographic Maps, Outcrop Patterns, and Structure Contours
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<strong>Lab</strong> 2:<strong>Topographic</strong> <strong>Maps</strong>, <strong>Outcrop</strong><br />
<strong>Patterns</strong>, <strong>and</strong> <strong>Structure</strong> <strong>Contours</strong>
<strong>Topographic</strong> <strong>Maps</strong><br />
• a 2-dimensional<br />
representation of a<br />
a 3-dimensional<br />
surface<br />
• one type of<br />
contour maps
Contour Lines<br />
• Contour lines<br />
1) lines of equal value<br />
(elevation)<br />
2) the intersection of<br />
horizontal planes with the<br />
ground surface<br />
• Index contours<br />
contour lines labeled<br />
with value (usually a<br />
heavier line)
Contour Intervals<br />
intermediate flat<br />
steep<br />
• Contour interval is the<br />
difference in the values of<br />
adjacent contour lines<br />
• Constant contour intervals<br />
• Closely spaced<br />
contours =><br />
Steep gradient<br />
•Widely spaced<br />
contours =><br />
Gentle gradient
Calculating Gradient <strong>and</strong> Angle<br />
a traverse line<br />
1) Measure its length to get the<br />
horizontal change (run)<br />
2) Count the number of contour<br />
lines cross it to get the<br />
vertical change (rise)<br />
Slope Fraction<br />
Gradient<br />
=<br />
rise<br />
run<br />
rise<br />
=<br />
run<br />
× 100%<br />
⎛ rise ⎞<br />
Slope Angle φ<br />
= arctan⎜<br />
⎟<br />
⎝ run ⎠
Rules for Contour Lines<br />
• Contour lines generally should not merge<br />
or cross<br />
• <strong>Contours</strong> should be either closed within<br />
the map area or truncated by the edge<br />
of the map<br />
• Contour lines are repeated to indicate<br />
reversals in gradient direction<br />
• <strong>Contours</strong> “V” point an upstream<br />
direction
Repeated Contour lines
Rule of “V’s”<br />
Contour lines “V” in an upstream direction<br />
where rivers or stream are present in the<br />
l<strong>and</strong>scape (topography)
<strong>Topographic</strong> Profiles<br />
Vertical Exaggeration<br />
=<br />
Vertical<br />
Scale<br />
=<br />
Horizontal Scale<br />
1<br />
1440<br />
1<br />
24000<br />
= 16.<br />
73×
Intersection of Planes<br />
with Topography<br />
•planes make<br />
distinct outcrop<br />
patterns when they<br />
intersect irregular<br />
topography<br />
• patterns depend on<br />
the gradient of the<br />
topography <strong>and</strong> the<br />
dip of bedding
Horizontal Planes<br />
Vertical Planes
Bedding dips upstream<br />
Bedding dips downstream<br />
Dip is less than stream<br />
gradient<br />
Bedding dips downstream<br />
Dip is the same as stream<br />
gradient<br />
Bedding dips downstream<br />
Dip is larger than stream<br />
gradient
<strong>Structure</strong>-Contour <strong>Structure</strong> Contour <strong>Maps</strong><br />
• A map on which<br />
contour lines represent<br />
lines of equal elevation<br />
on a structurally<br />
significant surface<br />
• The surface could be<br />
a marker bed, contact,<br />
unconformity or fault<br />
Surface Projection to<br />
Map View<br />
Cross Section
Bedding Dip<br />
Strike Direction<br />
135m structure-contour line<br />
150m structure-contour line<br />
Dip Direction
Bedding Thickness<br />
Horizontal Distance<br />
between the top <strong>and</strong><br />
bottom surfaces<br />
150m structure-contour<br />
line for top surface<br />
150m structure-contour<br />
line for bottom surface<br />
Dip Angle<br />
Cross Section<br />
Thickness
3-Point Point Problems<br />
• 3 point problems help us determine the<br />
attitude of bedding when all we know is the<br />
location of three points on the bed
<strong>Outcrop</strong> <strong>Patterns</strong> from Attitudes<br />
• by knowing the attitude of bedding at one point with respect to<br />
topography, we can predict the outcrop pattern of that unit<br />
across the l<strong>and</strong>scape
Overhead Demos…<br />
Demos