Visualizing horizontal contacts using Google Earth
Monocline in the
eastern Iran (32 24 50.95N, 56 47 00.19E). Click image to enlarge.
Once students have a good
visual grasp of inclined and vertical contacts, they move on to
horizontal contacts. The area at right in the eastern Dasht-e Lut of
Iran is a spectacular area for students to explore the transition between inclined contacts and horizontal contacts.
Because students are already familiar with the sawtooth pattern of
inclined units in areas with topography, they start by adding strike and
dip symbols to a printout of the area and sketch a cross section of the
western portion of the area.
The Google Earth 3D view allows students to visualize the relationship
between dip angle and the pattern of outcrop traces. Students work out
why the outcrop patterns in the central and eastern portions of the area
are so different from the western portion. Their introduction to map
interpretation ends with a discussion of the outcrop pattern of horizontal and very shallowly dipping contacts
Students finish this introductory section on mapping by making a concept sketch
of the map view (above) plus the oblique image (left)
to document their understanding of the influence of contact dip and
topography on outcrop patterns.
Mapping and cross section practice
Monument Upwarp, near Mexican Hat, Utah (37 09 15.44N, 109 49 20.24W).
Click image to enlarge.
Click to enlarge.
students have a good visual grasp of units, contacts, outcrop patterns,
and strike and dip, they are ready to use Google Earth to do more
complex mapping. The Raplee Anticline (part of the Monument Upwarp) in
southern Utah (right) is an ideal area for students to map and interpret complex patterns in relatively simple bedrock geology
The change in dip from horizontal at the
top to inclined at the base creates fantastic patterns that students
normally find difficult to interpret in map view (right). Having the
Google Earth 3D view (left) makes it possible for them to visualize how
the contacts and topography interact.
Students can also use elevations in Google
Earth to convince themselves that some of the contacts are horizontal
(the red stars on the image at left, for example, lie at approximately
the same elevation) and others are inclined (the blue stars lie at
progressively lower elevations to the west).
For homework, students define mappable units for the image at left, add
strikes and dips, determine the age sequence of units, and create a
cross section sketch.
Go to the next step: Visualizing folds
Go to Visualizing inclined
contacts - Visualizing strike &
dip - Visualizing vertical
contacts - Visualizing horizontal
contacts - Visualizing folds - Other mapping projects