May 28, 2012
Georneys with Dana- Part V: The Garnet Road
Posted by Evelyn Mervine
I apologize for a bit of a hiatus in posting. There were some technical troubles with the AGU blogs, and then my husband and I were down in Florida for five days. Blogging may continue to be somewhat light for the next few weeks, but I’ll post when I’m able. First, I’ll finish up my “Georneys with Dana” series. Then, I’ll post a bit about the trip to Florida.
Note: I convinced my Geokittehs co-author Dana Hunter to fly from Seattle to New Hampshire to visit me for a few days. I handed in the final version of my PhD thesis on Friday May 4th, and Dana arrived the next day to help me celebrate. This is Part V of my description of the fun georneys we had together during Dana’s visit.
Geologists, you may notice, often walk with their heads pointed downward. That’s because down is where the rocks generally are. Geologists also keep their heads pointed toward cliffs or boulders. When driving, geologists slow down and turn their heads when they pass roadcuts. At times, geologists become so absorbed in watching for rocks– and then looking closely at the interesting rocks they find– that they forget about the rest of the world: the scenery, other people, that squishy biology stuff, lunch, water, continuing the walk or hike that was started, driving at a normal highway speed, and so on.
Long before I began studying geology in a formal manner, I walked with my head pointed downward, looking out for interesting rocks. I guess that’s how I knew I should study geology. For example, my second week of high school I was going on a training run in the woods as part of my school’s Outdoor Program*. As I ran, I kept my eyes on the ground, keeping a casual eye out for interesting rocks. I ended up running straight into a tree. I went to the hospital for a few stitches, but I was generally okay. For the rest of the year, I was called “George” by my fellow students.
Before I learned much about rocks, I used to watch out for “pretty” rocks such as large pieces of rose quartz, silvery garnet schists, and rocks with bright red iron oxide weathering rims. Now that I know more about geology, I still enjoy finding “pretty” rocks, but I also find myself very interested in a wide variety of “ugly” rocks, such as highly-weathered peridotites, dull-colored sandstones, and gray basalts. That’s because even the dullest of rocks can tell fascinating stories.
To non-geologists, rocks are just something to walk upon or drive above or build a house upon; rocks are brown or gray or white hard things that are not worth paying much attention to unless they sink or shake or erupt… or perhaps if they are particularly sparkly. To geologists, rocks– even the dullest gray or brown rocks– are interesting, even when they are not particularly mobile or sparkly. That’s because geologists learn to read rocks the way people learn to read books. To a geologist, a rock’s features are like hieroglyphics. There are stories enfolded in the juxtaposition of two minerals, in the order of a set of veins, in the thickness of a lamination, in the offset of a fault, in the shape of a crystal, in the softness of a sediment, in the curve of a fossil,in the color of a weathering rind, in the roundness of a cobble, and in many other rock features.
Rock stories are almost always mysteries. The rocks provide clues, but it takes often quite a bit of work to figure out who murdered whom in what room with what weapon, so to speak. When reading rocks, geologists use various clues to try to figure out what crystallized from what and then squished into what under what conditions… or, perhaps, who died and was preserved into what that was then altered into what… or, perhaps, what settled onto what and then was filled with what… or, perhaps, what slid past what when and caused what size earthquake and tsunami. There are countless rock mystery stories.
Often, geologists barely begin to unravel rock mysteries in the field. Rocks must also be sampled and brought into the laboratory. Rocks must be cut up into thin slices and examined under microscopes; they must be scanned and crushed and dissolved and, sometimes, turned into plasma. Sometimes, rocks must be analyzed from space, using fancy satellites that provide much information about large and small-scale field features. Field observations of rocks must be carefully examined in the office: thousands of strikes and dips and other field information must be compiled and formed into geologic maps and models. Even then, geologists often only unravel part of a rock mystery. There is always more to learn about rocks. Like a good mystery novel, a rock story is rarely fully resolved; there are always loose ends left at the end; there are always sequel stories to unravel.
Because they can read rocks, geologists are easy to entertain. You don’t need a computer or a kindle or a television to entertain a geologist. All you need are some rocks– and there are rocks almost everywhere.
Here’s one recipe for entertaining two geologists for a morning:
1. Take two geologists.
2. Add one dog, two cameras, one hand lens, and one dirt road in New Hampshire.
3. Sprinkle the dirt road generously with freshly-broken, garnet-filled metamorphic rocks that are useful for stabilizing the road during spring “mud season.”
4. Tell the geologists to take the dog for a walk along the dirt road.
5. Busy yourself with something else while you wait for the two geologists to return. Note that geologists may take much longer to complete walks than non-geologists. A good rule of thumb, when the rocks are particularly interesting, is that geologists will take about two hours to complete a walk that takes non-geologists twenty minutes. If the geologists are too long in returning home, you may be able to lure them back by cracking open a few ice cold drinks.
Recipe warnings: The dog may periodically sit down in the middle of the road, looking forlornly at the geologists while they hunt for pretty garnet rocks in yet another section of the road. The geologists are likely to fill their pockets and camera bags full of rocks. Even for a “short” walk, it is advisable to send the geologists out fully equipped with water, sunscreen, and sun hats. Don’t bother sending snacks as the geologists will likely forget to eat the snacks.
I followed the above recipe when entertaining Dana last week. Dana served the role of “first geologist, I served the role of “second geologist” and Dingo (my parents’ pet) served the role of “the dog.”
Here are some pictures of our walk along the road which we nicknamed “The Garnet Road” because of all the crushed-up, garnet-bearing metamorphic rocks which were recently dumped on the road:
Here are some pictures of a few garnet-rich, metamorphic rocks which we collected along the road:
*My high school has a wonderful program called Outdoor in which students spent the semester learning about hiking, rock climbing, kayaking, and camping. Twice a week the students go on a longer trip, such as a kayaking trip. The rest of the week the students participate in short exercise and skill programs, such as going for a run and then learning how to set up a tent. I participated in Outdoor all four years of high school, and I greatly enjoyed the program.
Those photos are stunning. Where exactly is “The Garnet Road”?
With a geological setting as diverse as America’s every trip is promising with respect to the new geological features it has to offer you.
By the way, garnet crystals as large as these must be formed in an eclogitic facies. Considering that these rocks form deep in a subduction zone what are the chances of finding and eclogite on the ground?