Geology Professor, Callan Bentley @callanbentley: A Day in the GeoLife Series


Callan Bentley

NAME: Callan Bentley

CURRENT TITLE: Chancellor’s Commonwealth Professor of Geology, Northern Virginia Community College, Annandale, Virginia. I also blog at Mountain Beltway, tweet at @callanbentley, and serve as a contributing editor for EARTH magazine.

AREA OF EXPERTISE:  Geology, teaching

YEARS OF EXPERIENCE:  10 years on the job!

Master of Science, Science Education – Montana State University, Bozeman, Montana. July 2009.
Master of Science, Geology – The University of Maryland, College Park, Maryland. December 2004.
Bachelor of Science, Geology – The College of William and Mary, Williamsburg, Virginia. May 1996.


What’s your job like?

I teach introductory-level geology to a diverse group of students, and that’s lots of fun. I feel privileged to get to open many students’ eyes to the wonders of Earth science, to the immensity of geologic time and our place in the grand scheme of things. I get to share how the world looks through geology-colored glasses, and students report having a richer experience of life afterwards. A pretty rock is no longer just a pretty rock – it’s evidence of an ancient tectonic collision or an underwater avalanche. It’s a humbling and exciting new way to look at our lives on Earth!

Fort Valley, VA

Callan Bentley teaching geology in Fort Valley, VA (April 2016). Photo by Josh Chamot

There is no research expectation for faculty at my school, but I have a couple of initiatives that I am involved in. Most prominent is my geology outreach on the internet, including a blog and twitter feed, and to a lesser extent Facebook. I am a principal investigator (P.I.) on a grant from the National Science Foundation to make useful digital geology teaching media and to disseminate these products to those who can use them to teach and learn.

What’s a typical day like?

My days vary a lot. I live out in the Appalachian mountains, a long way from the campus where I teach, and I’m fortunate in that I only have to drive into school a couple of days each week. That means I have several long teaching days (a lecture and two labs or two lectures and one lab) on those days, plus office hours (plus several hours of listening to audiobooks or podcasts in the car!).

I wake up at home, work a little bit on the computer – something light on the brain like a blog post, answer easy emails, etc. Then I leave home around 9 a.m. (after rush hour) and drive to campus. On campus, I have office hours (really, more time for email and managing research/outreach initiatives), and then teach a lecture, followed by a lab, followed by more office hours and an evening class. I drive home around 9 p.m. It’s a long day.

However, the other days of the week, which are typical in their own way, involve working from home (online meetings, writing, GigaPan curatorial tasks), or heading out into the field to gather GigaPan images or scout out new samples, participate in colleague’s field trips, or deal with “life” stuff – like picking up my kid from school, going grocery shopping, mowing the lawn, doctor’s appointments, etc. The nice thing about these other days is I get to schedule my own time, and that’s really satisfying.

What’s fun?

Most of it is fun. I feel jazzed up about geology, and my own enthusiasm propels me forward and in many cases encourages my students to get excited, too.

My college supports field trips, so I’m delighted to lead several of these each year to local sites of interest. Each summer, I run a field course in the Rockies of Montana, and that is a formative experience for many students.


Callan Bentley on a field trip in Fort Valley, VA in April 2016. Photo by Dan Doctor, United States Geological Survey

What’s challenging?

Bureaucracy. NOVA, my college, is enormous. Getting stuff done – like planning for travel, or getting grant subawardees paid, or hiring students to serve as learning assistants, is a nightmare. The many levels of bureaucratic structure, the shifting rulebook, and delays in/absence of communication really discourage me from innovating. I do it anyhow, but each bureaucratic snafu adds to this accumulating pile that ultimately makes me want to simplify my work life.

What’s your advice to students?

Teaching at a two-year college is a great career. You get to inspire the next generation of geoscientists without the stress of “publish or perish,” tenure committees, or the need to have a PhD (all of which make the prospect of teaching at a 4-year university unappealing to me). It’s an ideal fit for someone like me, and maybe also for you. You should consider joining the National Association of Geoscience Teachers’ Geo2YC Division (two-year-college division). You should seek out opportunities to teach (TA) when you are working on your graduate degree, and you should be eager to inspire and guide your students towards their educational goals.

Professor Bentley

Chancellor’s Commonwealth Professor of Geology, Northern Virginia Community College, Annandale, Virginia.

Oh no! Why is there a sinkhole in your backyard?

The worst sinkhole I’ve ever seen developed at an 84-year-old man’s Brooksville, Florida home following tropical storm Debby last year.  At first, the house and property became inundated with water, but then sinkholes began opening up in the front yard.  You couldn’t help but stare when driving by, as the size of the sinkholes directly in front of the house seemed ominous. Luckily, he was saved by his neighbors.    If you’d like to read the news article related to this story, see:

So, why are there sinkholes prevalent in some areas of the world and not others?  The key is the type of rock below the land’s surface.  In some areas of the world, the land is underlain by carbonate limestone which is prime for sinkhole development.  Why?  Because this type of limestone erodes easily when exposed to rainwater that has become more acidic while percolating down through the surface layers.  Once the water reaches the limestone, it finds preferential pathways through the rock, dissolving it away and leaving behind voids.  As time passes, and I’m talking geologic time here, so thousands of years, these voids grow larger and eventually can collapse, causing the layers above to sink into the voids. Other factors including groundwater pumping, drought followed by large rainfall events and other changes to the pressure within the aquifer can also contribute to sinkhole formation.  Once a landscape is riddled with sinkholes and caves, it is typically referred to as a karst landscape. If you’d like to know more about the how and why of sinkhole formation, the St. John’s River Water Management District in Florida has a nice summary at Also, the Southwest Florida Water Management District has a helpful illustration on sinkhole formation as provided below.

The Making of a Sinkhole


The figure shows an example sinkhole caused by numerous factors including vibrations from construction, local groundwater pumping, pressure from standing water and rainfall percolation through acidic layers.

There are a couple of sinkhole types I’d like to mention.  First is the subsidence or solution sinkhole and these gradually form depressions in the landscape, sometimes forming ponds or lakes as in the picture below.



These sinkholes can also be seen within water bodies such as lakes and oceans.

The second type is a collapse sinkhole and this type can be quite catastrophic such as the one in Guatamala in 2010. Here’s a great shot of that sinkhole: This sinkhole event followed a volcanic eruption and tropical storm, and the sinkhole swallowed a factory and intersection.

The cause of these types of sinkholes are illustrated below:



As you can see, the roof of the cavity gives way and forms a tubular-type void, causing the land surface to collapse and a large, deep sinkhole forms.

Unfortunately, there’s no way to predict when a sinkhole will occur.  For Florida, you can find additional information on sinkholes at the following link to the Florida Geological Survey through the Department of Environmental Protection:

If you have any examples of sinkholes in your area, please feel free to leave information in the comment box below!



The best rock cycle diagram I have ever seen!

I’ve gotta admit, as geeky as this sounds, I’m pretty excited over this rock cycle diagram I found at  I wish I had this available while I was in college, because it not only shows the different processes in the rock cycle (i.e. deposition), but it also shows the types of rocks (igneous, metamorphic and sedimentary) that are formed in the different geologic settings (volcanism, plutonism, tectonism).  For example, in the case of metamorphic rocks, it illustrates that with heat and pressure the rocks transform to gneiss and schist.  Unless, I’m missing it, I don’t see phyllite, though which would have been helpful.  It also shows the different types of conformities, as well as faulting types and numerous geologic terms. So, if you are a student in geology, I highly recommend reviewing this rock cycle diagram.  It will give you a better understanding than the traditional rock cycle diagrams of old.