Lab 2:Topographic Maps, Outcrop Patterns, and Structure Contours

Lab 2:Topographic Maps, Outcrop
Patterns, and Structure Contours

Topographic Maps
• a 2-dimensional
representation of a
a 3-dimensional
surface
• one type of
contour maps

Contour Lines
• Contour lines
1) lines of equal value
(elevation)
2) the intersection of
horizontal planes with the
ground surface
• Index contours
contour lines labeled
with value (usually a
heavier line)

Contour Intervals
intermediate flat
steep
• Contour interval is the
difference in the values of
adjacent contour lines
• Constant contour intervals
• Closely spaced
contours =>
Steep gradient
•Widely spaced
contours =>
Gentle gradient

Calculating Gradient and Angle
a traverse line
1) Measure its length to get the
horizontal change (run)
2) Count the number of contour
lines cross it to get the
vertical change (rise)
Slope Fraction
Gradient
=
rise
run
rise
=
run
× 100%
⎛ rise ⎞
Slope Angle φ
= arctan⎜
⎟
⎝ run ⎠

Rules for Contour Lines
• Contour lines generally should not merge
or cross
• Contours should be either closed within
the map area or truncated by the edge
of the map
• Contour lines are repeated to indicate
reversals in gradient direction
• Contours “V” point an upstream
direction

Repeated Contour lines

Rule of “V’s”
Contour lines “V” in an upstream direction
where rivers or stream are present in the
landscape (topography)

Topographic Profiles
Vertical Exaggeration
=
Vertical
Scale
=
Horizontal Scale
1
1440
1
24000
= 16.
73×

Intersection of Planes
with Topography
•planes make
distinct outcrop
patterns when they
intersect irregular
topography
• patterns depend on
the gradient of the
topography and the
dip of bedding

Horizontal Planes
Vertical Planes

Bedding dips upstream
Bedding dips downstream
Dip is less than stream
gradient
Bedding dips downstream
Dip is the same as stream
gradient
Bedding dips downstream
Dip is larger than stream
gradient

Structure-Contour Structure Contour Maps
• A map on which
contour lines represent
lines of equal elevation
on a structurally
significant surface
• The surface could be
a marker bed, contact,
unconformity or fault
Surface Projection to
Map View
Cross Section

Bedding Dip
Strike Direction
135m structure-contour line
150m structure-contour line
Dip Direction

Bedding Thickness
Horizontal Distance
between the top and
bottom surfaces
150m structure-contour
line for top surface
150m structure-contour
line for bottom surface
Dip Angle
Cross Section
Thickness

3-Point Point Problems
• 3 point problems help us determine the
attitude of bedding when all we know is the
location of three points on the bed

Outcrop Patterns from Attitudes
• by knowing the attitude of bedding at one point with respect to
topography, we can predict the outcrop pattern of that unit
across the landscape

Overhead Demos…
Demos