Tag Archives: Surveying

Geoscientist’s Toolkit: QGIS

QGIS screenshot, showing Heard Island.  Brown is land/rock, blue are lagoons, and the dotted white is glacier.
QGIS screenshot, showing Heard Island. Brown is land/rock, blue are lagoons, and the dotted white is glacier.

One of a geoscientist’s most useful tools is a geographic information system, or GIS. This is a computer program which allows the creation and analysis of maps and spatial data. Perhaps the most widely used in academia is ArcGIS, from ESRI. However, as a student and hobbyist who likes to support the open-source software ecosystem, I use the free/open-source QGIS.

QGIS can be used to make geologic maps of an area, chart streams, and note where certain geologic features (e.g. volcanic cones) are present. For instance, at the top of this post is a map of Heard Island that I’ve been playing with, from the Australian Antarctic Division. It is composed of three different layers, each published in 2009: an island layer (base, brown), a lagoon layer (middle, blue), and a glacier layer (top, dotted bluish-white).

I believe I have mentioned here previously that one interesting thing about working with Heard Island is that with major surface changes underway (glacial retreat, erosion, minor volcanic activity), the maps become obsolete fairly quickly. This week I have been learning about creating polygons in a layer, so that I can recreate a geologic map from Barling et al. 1994.[1] One issue I’ve come up against, though, is that the 1994 paper has some areas covered in glacier (from 1986/7 field work), whereas my 2009 glacier extent map shows them to be presently uncovered. In fact, even the 2009 map shows a tongue of glacier protruding into Stephenson Lagoon (in the southeast corner), while recent satellite imagery shows no such tongue.

During the Heard Island Expedition in March and April, 2016, I hope that we will have time to go do a little geologic mapping. Creating some datasets showing the extent of glaciation (particularly along the eastern half of the island) and vegetation, as well as updating the geologic map to include portions which were glaciated in 1986/7, would be a worthwhile and seemingly straightforward project.

QGIS itself is much more than a mapping tool (not that I know how to use it), and can analyze numeric data which is spatially distributed, like the concentration of chromium in soil or water samples from different places on a study site. QGIS provides a free way to get your hands dirty with spatial data and mapping, and is powerful enough to use professionally. Users around the globe share information on how to use it, and contribute to its development.

For those looking to go into geoscience as a career, I would strongly recommend learning how to use it. I didn’t learn GIS in college (chemists don’t use it much), and somehow avoided it in grad school. But I regret not having put time in to learn it sooner. There’s all kinds of interesting spatial data, and a good job market for people with a GIS skillset (or so I hear). I have only scratched the surface of QGIS’s capabilities with my use of it, but I definitely intend to keep learning. You can probably follow the day-to-day frustrations and victories on my Twitter account (@i_rockhopper).

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[1] Barling, J.; Goldstein, S. L.; Nicholls, I. A. 1994 “Geochemistry of Heard Island (Southern Indian Ocean): Characterization of an Enriched Mantle Component and Implications for Enrichment of the Sub-Indian Ocean Mantle” Journal of Petrology 35, p. 1017–1053. doi: 10.1093/petrology/35.4.1017

Exploring Capitol Rock, MT

Wide-angle view of Capitol Rock, MT.  Image credit: Bill Mitchell (CC-BY)
Wide-angle view of Capitol Rock, MT. Image credit: Bill Mitchell (CC-BY)

Several weeks ago, I took a road trip with some friends across the northern part of South Dakota as part of a ham radio adventure. When we reached northwestern South Dakota, we were having so much fun that we decided to continue into just across the border into Montana.

At the state line between South Dakota and Montana, we found that there was a relatively high point (Capitol Rock) which we could probably access with our vehicle. Capitol Rock is in a national forest, so no permission would be needed to go there. It would be a good place to do ham radio (primary goal), and it would get me close to some rocks (bonus)!

As we drew closer to the summit of the hills, I couldn’t help but think that the rocks looked a lot like the ones in my research area in northeastern Montana, in the Hell Creek region (Hell Creek and Tullock/Fort Union Formations).[1]

Sadly, I didn’t get quite as close to the outcrops as I would have liked (we were on a bit of a schedule), but I did get some pictures and made a few observations.

North half of Capitol Rock.  Image credit: Bill Mitchell (CC-BY).
North half of Capitol Rock. Image credit: Bill Mitchell (CC-BY).

Here we had flat-lying sedimentary strata, presumably of roughly Cretaceous-Paleogene age (somewhere around 80-50 million years ago, Ma) (introduction to geologic time). These would have been shallow marine or terrestrial sediments from along the western interior seaway, which was on its way out at the end of the Cretaceous (66 Ma, [1]). I would expect to find some fossils preserved in the sediments, and from those, a fairly accurate date on the strata could be obtained. There may even be some volcanic ash deposits which would allow for direct dating using the U-Pb system or the K-Ar system (Ar/Ar dating) .

At the top of Capitol Rock were several massive units with a slight orange color (probably from oxidized iron). Beneath those were some more finely bedded strata, with bed thicknesses probably around 3-10 cm (eyeball estimation), and displaying some rough texture (popcorn texture?). Underneath those were some fairly easily eroded strata of generally uniform grey color. The image below has these observations annotated.

Northern portion of Capitol Rock, annotated.  Image credit: Bill Mitchell (CC-BY)
Northern portion of Capitol Rock, annotated. Image credit: Bill Mitchell (CC-BY)

The ground under my feet for that previous picture was still above average terrain. Here is an additional picture, taken from the south (looking north), which shows that the light-grey sediments are underlain by more yellow-orange units.

Distant photograph of the lower portion of stratigraphy underlying Capitol Rock.  Image credit: Bill Mitchell (CC-BY).
Distant photograph of the lower portion of stratigraphy underlying Capitol Rock. Image credit: Bill Mitchell (CC-BY).

Upon returning home, I decided to see what description I could find online of Capitol Rock’s geology. It seems there are a number of different descriptions of it.

Capitol Rock, located in the Long Pines Unit in Montana, is a massive white limestone uplift that resembles the Nation’s capitol building.
Montana Office of Tourism

Capitol Rock, located in the Long Pines land unit in Montana, is a massive white sandstone remnant which originated as a volcanic ash deposit. This unique formation resembles the Nation’s Capitol Building in Washington, DC.
US Forest Service

The Bureau of Land Management (BLM) has an interesting discussion of the geology of this area from the perspective of firefighting, specifically in the avoidance of fibrous or asbestos-like minerals which are present in some of the formations in the area:

Brule Member, White River Formation [ed: Formations are a larger stratigraphic unit, and can include multiple Members] – may only be present at Capitol Rock (SE 1/4 sec. 17; T3S; R.62 E) in the Montana portion of the Sioux District. Located at the base of the Arikaree Formation. Massive pinkish gray, calcium containing, clayey siltstone: nodular claystone: and channel sandstone. Contains abundant vertebrate fossils. Thickness 0-30 ft. The member is composed of massive pink clay, exposed in the badlands just Southeast of Reva Gap, well-bedded, hard pale green sandstones alternation with very pale brownish gray clay.
Weathering causes a tread and riser affect much like a staircase. Both the sandstone and the clay are generally calcareous and Bentonitic. The lower portion of the vertical cliffs in Slim Buttes is generally Brule.

Chadron Member, White River Formation – only located in the southern Long Pines within Montana. Found at the base of the Arikaree formation and beneath the Brule Formation at Capitol [R]ock (SE 1/4 sec. 17 T, 3 S., R. 62 E). Basal conglomerate sandstone overlain by beds 10 to 15 ft
thick of dark gray bentonite and cream colored siltstone. Thickness 0-100 ft.
Bureau of Land Management

Well, that’s a puzzling bunch of information, isn’t it! Various sources are suggesting limestone, sandstone from volcanic ash, and a mix of sandstone and siltstone. There’s one more source to check, too: the geologic map. Specifically, we’re interested in the Ekalaka 30’x60′ quadrangle from the Montana Bureau of Mines and Geology!

In the geologic map (look along the right [eastern] edge, near the “T 19N” mark; Capitol Rock is ~1 km NE of the “Tar” label] we see the Fort Union Formation (informal Ekalaka member) at the base of the hills (i.e., under my feet), which is consistent with observations and the relatively detailed presentation from the BLM. It is also consistent with my experience that the Fort Union Formation is generally yellow-orange (in contrast to the drab, grey of the Hell Creek Formation). Then things get trickier. The rocks right at Capitol Rock are mapped as “Tar”, which is the Tertiary Arikaree Formation.

So, what is the Arikaree Formation? Well, the USGS has this to say:

Arikaree formation: gray sandstone with layers of concretions; contains volcanic ash and, locally, channels filled with conglomerate; known only in southeastern Montana.

On the other hand, the North Dakota Department of Mineral Resources breaks the Chadron, Brule, and Arikaree into distinct formations unto themselves.

I suspect this is all hitting at an important point: mapping is really hard, as is saying the rocks over here are the same as the rocks 40 km away. These difficulties are compounded when different scientists use different terminology, such as when the mapping is done by state geological surveys. The same rocks may change names when a state boundary is passed. Sometimes researchers will use the terminology from one state to apply to the rocks on both sides of the boundary, and then the literature is filled with multiple terminologies for the same rocks. It can also be very difficult to correlate rocks laterally over large distances, especially when there is poor outcrop over those distances (i.e. between buttes).

Here’s my interpretation of what’s going on at Capitol Rock: it is composed of siltstone, sandstone, and altered volcanic ash [still good for U-Pb dating!]. This volcanic ash is high in erionite, an asbestos-like mineral. Naming of the unit could include either the Arikaree Formation, or the Brule Member of the White River Formation. An age of 37–30 Ma seems reasonable.

***

[1] Renne, P. R., Deino, A. L., Hilgen, F. J., Kuiper, K. F., Mark, D. F., Mitchell, W. S., III, Morgan, L. E., Mundil, R., Smit, J. (2013) Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary. Science 339: 684-687, doi: 10.1126/science.1230492.

Geoscientist’s Toolkit: Scale Bars

Zircon grains, without scale bar.  Image credit: Bill Mitchell
Zircon grains, without scale bar. Image credit: Bill Mitchell

Scales are useful. Many times a picture alone may not give adequate information about the scale, particularly absent recognisable objects or vegetation. For instance, the zircon crystals above have no scale: how long do you think they are? (answer below!)

Similarly, this outcrop photo does not have a scale either. How large are the beds in the fold?

Fold in outcrop, without scale.  Image credit: Bill Mitchell
Fold in outcrop, without scale. Image credit: Bill Mitchell

In the geosciences, a sense of scale is particularly important. Without it, these images lose context which may be important to their interpretation.

Let’s see how you did.

The zircons are around 100-150 microns long. For context, a standard piece of copier paper is around 100 microns thick.

Zircon grains, with scale bar.  Image credit: Bill Mitchell
Zircon grains, with scale bar. Image credit: Bill Mitchell

How about the outcrop? Here’s another picture, with a pen in the lower left for scale.

Fold in outcrop, with scale.  Image credit: Bill Mitchell
Fold in outcrop, with scale. Image credit: Bill Mitchell

Those are two examples of ways to put scale bars in. The first is by calibration of the relation between pixels and size for a microscope. The second is by the addition of a common object.

Another way to be particularly quantitative about the scale bar is to include a scale in the photo itself, as below. Off to the left you can see the edge of a small whiteboard, which is used to write the sample name and latitude/longitude coordinates for future reference. It’s the old-fashioned way to embed metadata, and is great for when you get back from your field work and are wondering what the heck your picture is actually of.

Volcanic ash, with scale bar for scale.   Image credit: Bill Mitchell.
Volcanic ash, with scale bar for scale. Image credit: Bill Mitchell.

Such emphasis on scale may seem pedantic for many field or lab photos. However, in environments where there is little available to give a sense of scale, such as the polar regions, or deserts, scale is an important thing.[1] This is a key consideration to keep in mind when travelling to places like Heard Island, where the scale will not necessarily be apparent without additional effort to include it within the pictures.

[1] Gould, L. M. Cold: The Record of an Antarctic Sledge Journey. New York, Brewer, Warren & Putnam, 1931.

Topographic Map(s) of Heard Island, and a Big Landslide

Heard Island Map, 1985.  Image credit: excerpt from the Division of National Mapping.
Heard Island Map, 1985. Image credit: excerpt from the Division of National Mapping.

A few days ago, I posted about topographic maps, including a discussion of how a small army of small surveyors made one of my local park. At Heard Island, surveying isn’t a walk in the park.

Many maps have been made of Heard Island, showing the topography and general geographic features of the island, and sometimes including the locations of major macrofauna (penguins, elephant seals, etc.).[1] An excerpt I made from one produced in 1985 is shown above. Although there are more recent maps available, including maps with higher topographic resolution, this one is more visually illustrative of the landforms.

Maps of Heard Island are difficult to produce, in part because there is a dearth of high-resolution, high-quality data. In most parts of the developed world, detailed topographic maps are made not through boots-on-the-ground surveying but by airborne LiDAR. For instance, aerial imagery and LiDAR provided very useful data for understanding the Oso landslide in Washington state. However, aerial flights over Heard Island are much less frequent, and mapping efforts there come without the obvious benefits to the local populace.

LiDAR map near the Oso landslide (red region at right), and a larger landslide complex (red region at center).  Image credit: Dan McShane.
LiDAR map near the Oso landslide (red region at right), and a larger landslide complex (red region at center). Image credit: Dan McShane.

Surveying the whole island by foot at high detail is untenable, because the area is quite large, the terrain difficult, and the weather inclement, even in the summer. However, portions have been mapped by hand (and theodolite).

But perhaps the biggest challenge Heard Island presents to cartographers is the rapidity of its changes. Volcanic eruptions can add new land to the island, or make parts higher. Glaciers can carve out the rocks and leave them as till, sometimes in the ocean, sometimes in the lagoons, and sometimes as moraines on the land. Not only can the glaciers carve out the rocks, but as less snow accumulates on the glaciers than is lost to melting, the glaciers will retreat. This opens up new land which before had been covered in ice. Stephenson Glacier, on the southeast corner of Heard Island, has retreated significantly in the last 60-70 years, revealing a great deal of new terrain.

Steep slopes and the very wet environment (lots of snow and rain) lead to very high rates of erosion. Outwash channels from the glaciers can carve into the rock and transport sediment into lagoons and near-shore areas.

Finally, there’s another agent of change: landslides. Take a look at the LiDAR image above, showing the landslide region. Now take a look at the southwest portion of the Heard Island shown at the top of the post. The curving crest along the north and east sides of the volcano, as well as the ridge extending to the south-southwest are interpreted to be the boundary (technical term: scarp) of a debris avalanche (a landslide-like process).[2]

Taken as a whole, these processes change the landscape significantly on a decade-to-century timescale, if not even more rapidly. This is why making maps and keeping them current is so valuable: it give us a way to see how the landscape is changing over time. Perhaps the upcoming Heard Island Expedition will do some mapping and be able to provide updates which reflect the latest changes at Heard Island.

[1] https://www1.data.antarctica.gov.au/aadc/mapcat/list_view.cfm?list_id=1, accessed Feb. 6, 2015. Free registration required for map download.

[2] Quilty, P. G. & Wheller, G. 2000; Heard Island and The McDonald Islands: a Window into the Kerguelen Plateau. Papers and Proceedings of the Royal Society of Tasmania. 133 (2), 1–12.