Geoscientist’s Toolkit: Geologic Map

Geologic map of Minnesota bedrock.  Image credit: scaled down from University of Minnesota/Minnesota Geological Survey.
Geologic map of Minnesota bedrock. Image credit: scaled down from University of Minnesota/Minnesota Geological Survey (original, 11 MB PDF).

Maps are neat. Geologic maps in particular can be quite interesting (see above, particularly the original PDF). These are the product of detailed surveys, which are undertaken both at the federal and state level, and show which rock types are found in which regions. Some of these rocks can be traced over long distances (like the sedimentary rocks of the southeastern corner of Minnesota), while others are localized.

Geologic maps give a summary of what types of rocks are in which areas. From this, you can find out search terms to get you to more information about certain rocks, or you can use the rock type to determine what used to be happening in an area. For instance, southeastern Minnesota was once covered by a warm, shallow sea, leading to sandstone, limestone, and dolostone formation. Some of the limestones are fossiliferous. Northeastern Minnesota used to be home to a volcanic rift valley (like the one presently in East Africa) and is home to volcanic rocks, such as the North Shore Volcanic Group.

In addition to the short description of the rock units, geologic maps will give the estimated age range of the rocks (if you need a refresher on geologic time, see this post). A quick glance at the time scale will show you that although you may find fossils in southeastern Minnesota, don’t expect to find any dinosaurs (they existed during the Mesozoic)!

Faults are mapped as well, either transform (offset side-to-side), thrust (compressing, one side going up), or normal (expanding, one side falling). Dikes, which are ribbon-like intrusions which cut through the local rock, are mapped as lines. Because they need to cut through the local rock, they are inherently younger than the rock which they cut through—thus a radioisotopic age for the dike will be a minimum age for the unit it intrudes.

There are also several different types of geologic maps. Bedrock maps, such as the one above, show what the primary consolidated rock is, although it may be buried beneath loosely packed, more recent sediments. Surficial maps show more recent deposits; here in Minnesota, that’s often glacial deposits of various types, but can also include features such as alluvial fans and landslide deposits.

Finding geologic maps here in the US can be a little bit tricky. The USGS has nice geologic maps (start here), but they tend to be large-area. State surveys seem to have more detailed local maps, but each state has their maps in a different location and the availability may not be consistent state to state. Montana has a nice geologic map interface on their website, while Minnesota’s geologic maps are not easily found—there are county-scale surficial geologic maps, at least for some counties, but I’ve really only been able to find them through third-party search engines. For advanced map users, the state surveys will often make the raw GIS (geographic information system) data available.

Silicic dike in the Benton Range, near Bishop, CA. Image credit: Bill Mitchell.
Silicic dike in the Benton Range, near Bishop, CA. Image credit: Bill Mitchell.

Geoscientist’s Toolkit: SERC

Have you ever developed your own activities for doing outreach related to your research? Or wanted to find a way to teach a geoscience concept to a class?

There is a great resource available for this kind of thing: the Science Education Resource Center, at Carleton College [my alma mater].

From demos to lab ideas to tutorials on how certain types of equipment work, SERC has lots of great material. Of course, it doesn’t just appear out of nowhere. If you have taken the time to develop an interesting and useful activity, guide, or lab, you can submit the materials for others to use (under a Creative Commons license).

I have used SERC to get activities on dinosaurs (this one on calculating the speed of dinosaurs was awesome!), as well as to find good resources on mineralogy (my background as a chemist left me a bit behind mineralogy/petrology when I joined an Earth Science research group). There are activities and discussions around topographic maps, glaciers, climate change, groundwater, and the geologic timescale (my introduction to the geologic timescale, which isn’t on SERC, can be found here).

SERC is a great resource, and they hold workshops/webinars too!

Physical Preparations

Cross-country skiing in Minnesota.
Cross-country skiing in Minnesota.

Going on an expedition to Heard Island will require me to be in good physical condition. There are tents, generators, and other gear to haul. Hiking around on the island may be a bit treacherous, with burrows for nesting seabirds scattered across the already uneven terrain.

In preparation, I’m adding activity to my usual routine: more running, biking, backpacking, and, come winter, cross-country skiing. Some of my college friends (and cousins) convinced me to sign up for a hilly 51 km ski race next February, and others have been trying to get me to register for a 24-hour run/walk (for which I was a support crew member this year).

Fortunately, most of this preparation falls in with what I was already hoping to do. Riding my bike around town more is good for my health and reduces fossil fuel usage. Running, biking, and backpacking will keep me in shape for skiing once the snow starts to fall (despite Minnesota’s reputation, it will probably be at least October before there’s enough snow to ski on). And, of course, backpacking tends to lead to adventures of its own. Perhaps I’ll hike part of the Superior Trail (along the north shore of Lake Superior), or some of the trails in the Boundary Waters Canoe Area.

Getting myself into shape for this expedition probably won’t be a huge deal (I’m not trying to lose weight for it), but if I want to be competitive with the ol’ ski team friends (and cousins), I need to step it up a notch or two. Were I to do the 24-hour run/walk, the goal would be to complete a marathon—I don’t think I’ve ever pushed past 10 miles in one run.

Geoscientist’s Toolkit: Secchi Disk

Secchi disk being lowered into the water to measure water clarity.  Image credit: J. Albert Bowden II (CC-BY).
Secchi disk being lowered into the water to measure water clarity. Image credit: J. Albert Bowden II (CC-BY).

Some lakes and rivers are very clear, while others are very murky with sediment or organic material. Water clarity can yield information about what kind of environment is present around the water body (in its watershed). My local lake is fairly murky, due to significant nitrogen and phosphorous in the run-off from the many well-tended lawns in the area.

Secchi disks, are 20-30 cm diameter disks, generally white (freshwater disks generally have two black quadrants on them as well). These disks have a line attached to their center, and are lowered down into the water until they are just barely visible. That depth is the Secchi depth, and would be recorded.

In the Boundary Waters of northern Minnesota, scientists are interested in how the water quality of the lakes are changing. If you’re headed up there on a canoe trip, you can volunteer to take secchi depth measurements.

Getting secchi depth measurements in the lagoons and near-shore waters of Heard Island could be an interesting project, too.