Visualizing Vertical Contacts

Initial Publication Date: June 26, 2012

Visualizing vertical contacts using Google Earth Barbara Tewksbury (Hamilton College)

Vertical dike on the flank of the Spanish Peaks, CO (37 23 36.05N, 104 50 54.71W)

Once students have a good visual grasp of inclined contacts and strike and dip, they explore the two special cases of vertical and horizontal contacts. Although it seems backwards to start with the harder concept of inclined contacts, my students seem to benefit from spending more time on inclined contacts first. Then, using Google Earth, they breeze through vertical and horizontal contacts and their outcrop patterns in areas with topography.

The vertical dikes radiating from the Spanish Peaks near Walsenburg, CO (right) are outstanding for teaching students about vertical contacts.

Click to enlarge.

In class, students first explore one of the vertical dikes extending east from the Spanish PeaKs. In vertical view (top left), the outcrop pattern is nearly a straight line, but a tilted view (middle) shows that the dike is eroded into the same kind of Vs that they have already seen. An end-on tilted view (bottom) shows clearly why the Vs don't show up in a bird's-eye view.

One of the dikes extending north from the Spanish Peaks shows spectacular shadows that confirm, even in a vertical view (below), that the dike is eroded into connected fins but still has a straight line outcrop trace.