Initial Publication Date: June 26, 2012
Visualizing dip and strike using Google Earth
Barbara Tewksbury (Hamilton College)
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Once students have
done their first mapping exercise and
have a good visual grasp of inclined units and contacts, they explore
the south flank of a spectacular plunging anticline near Khvorgu, Iran
(right). In the classroom activity described below, students learn first about dip and then about strike,
which is opposite to the typical order for teaching the two concepts.
This seems to work well, because dip is actually a more intuitive
concept than is strike.
In class, students begin by viewing the inclined layers in Google Earth, as they did for the mapping homework described on the previous web page. I use the Google Earth view (below) to correlate the term "inclined/tilted" with the new term "dip", and students determine the approximate dip amount and dip direction for the contacts.
I ask students to make a quick cross section sketch showing the topographic profile and the inclined contacts. We reason out that the slope of the flatirons isn't really an accurate measure of dip of the contacts and that we need a dip line on the contact itself, rather than on the slope.
We then generate two horizontal lines on the contact in Google Earth (red lines above right) by connecting points of equal elevation on the sides of the flatirons with a line using the Google Earth draw path tool, and we then calculate the dip of the contact using distances determined using the Google Earth measure tool. (Note: it just happens to work out in this particular spot, although in most places the results are erratic because of the limitations of the elevation data set in Google Earth.)
For homework, students define mappable units, locate contacts, create a geologic sketch map, add strikes and dips, and work out which unit is the oldest. They also make a cross section sketch. Being able to view the area in the Google Earth 3D view is instrumental in helping them make the cross section.
Go to the next step: Visualizing vertical contacts
Go to Visualizing inclined contacts - Visualizing strike & dip - Visualizing vertical contacts - Visualizing horizontal contacts - Visualizing folds - Other mapping projects