CRG Colloquium Series

The USGS Central Region Colloquium Series is proud to present free lectures by our preeminent scientists located throughout the region. Guest lectures by agency and university partners are also presented. Topics include earth and life science issues such as wildfire, earthquake, and flood hazards; energy resources; climate change; invasive species; and wildlife resources.

Presentations are open to the public and are given on Thursday afternoons from 1:30 to 2:30 p.m. in the Denver Federal Center’s Foord Lecture Room, located in Building 20 (room B-1409; use entrance W-3).

We hope that you will find an opportunity to participate in the USGS Central Region Colloquium Series, whether as a contributor or attendee.

Tuesday, November 24 @ 10:30, Building 20 - Tweto Room B-1207

Formation of Sheeting Joints – a New View

Stephen Martel, University of Hawaii at Manoa

rock fractures

A fundamental relationship, derived from the equation of static equilibrium, illuminates how the shape of a curved traction-free surface, the surface-parallel stresses, and gravitational body forces contribute to fracturing subparallel to the surface. A surface-normal tension arises if σ11k1 + σ22k2 > ρg cosβ, where k1 and k2 are the principal curvatures at the surface, σ11 and σ22 are the normal stresses parallel to the respective principal curvature arcs, ρ is material density, g is gravitational acceleration, and β is the slope. This general result, valid for any solid, explains why sheeting joints (prominent opening mode rock fractures subparallel to the topographic surface) develop where compressive stresses parallel to the surface are sufficiently high (negative) and at least one principal curvature is sufficiently convex (negative). Among other things, this relationship also could be used to predict where particular dangerous fractures would be in slopes prone to rock fall.

Hosted by the USGS Geologic Discipline, Earth Surface Processes Team. For questions or to talk to Steve during his visit, please contact Scott Minor, 303-236-0303,

How to Participate
Peter Modreski (303-202-4766) is the series coordinator.  If you wish to schedule a lecture or presentation, please contact the appropriate discipline science coordinator.

This is a Cyber Talk

Concurrently presented via the Internet

How to participate via the Web:

If you would like to connect to view this meeting over the internet or by audio via teleconference bridge:
Please send an email message (in advance) to Pete Modreski at

He will respond by forwarding an e-invitation to you, which will give instructions and the exact url from which you can register to participate in this meeting online.

Anyone in or outside of the USGS may do this and there is no extra charge for the call, but it is a long distance call to Reston, VA.

If you have any questions, please contact Pete Modreski, 303-202-4766,

Listserv Notification of Upcoming Presentations

To receive e-mail notification of upcoming presentations, please send the following email message to

Subscribe CR-USGS-colloquium <enter your name>


Subscribe CR-USGS-colloquium George Geologist

Central Region:      Biology   CR-Intranet   Geography   Geology   Water
FirstGov button  Take Pride in America button