Geoscientist’s Toolkit: Paleomagnetic Coring

Recording rock core orientation for paleomagnetic analysis. Image credit: Bill Mitchell.

I’ve touched on paleomagnetism a little bit before, both as a technique for tying rocks in to the geologic timescale, and as something which can be found by using a fluxgate magnetometer. It’s a pretty interesting set of techniques and uses some cool science tools, so I thought I’d explain a little bit more.

Magnetism from the Earth’s magnetic field can be retained by individual layers of rocks, at least under some circumstances. If you have a bunch of layers stacked on top of each other like pancakes, the different layers (beds) can have different magnetic directions.

Stack of banana-walnut pancakes. Although probably low on magnetic minerals and too thin individually for magnetic coring, they do illustrate the concept of layering quite nicely. Image credit: Jack and Jason’s Pancakes (CC-BY-SA).

As you might expect, the equipment needed to make sensitive measurements of the magnetic field are not particularly portable (and may be a topic for another post). Samples need to be collected in the field and brought back to the lab, and the sample orientation must be marked and recorded in such a way that the measured magnetic field can be related back to the magnetic field in the rock itself.*

To do that, paleomagnetists (or paleomagicians) will drill a small (1″ diameter by a few inches long) annular hole into the rock, leaving a plug of rock in the center. That will become the sample. Before it can be removed from the hole, a mark is made on the top of the plug with a brass rod. The direction of the hole is determined with a compass (or a sun compass when conditions allow), as is the angle away from vertical of the core (the hade).

When the plug is freed from the rock, the down-hole direction is marked with arrows along the mark using a permanent marker. The samples (several from each bed) are then placed into sample bags, labelled appropriately, and carefully transported back to the lab.

Are you irresistibly attracted to such a magnetic field of study? This is probably the best place to go for more information, and is freely accessible online.[1]

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[1] Tauxe, L., Banerjee, S.K., Butler, R.F. and van der Voo R, Essentials of Paleomagnetism, 3rd Web Edition, 2014. [accessed Aug. 27, 2015]

* The field magnetic field?

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Geoscientist’s Toolkit: QGIS

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

Heard Island Expedition Update: T-7 Months

Visualization of a proposed Heard Island shelter setup, using two HDT Global airbeam tents. Each shelter is 20’x21′. Image credit: Bob Schmieder [?].

It’s only seven months until the Heard Island expedition leaves Cape Town, South Africa, heading for Heard Island. Preparations are really beginning to get going!

This morning (Minnesota time) we had a conference call with the entire on-island team (such as were able to join). Scheduling that can be tricky, because we have team members scattered around the globe, including from Australia, the US, and Ukraine.

From the conference call, it was clear that things are coming along nicely. We are gaining familiarity at least with the voices of other team members, so that when people are speaking they don’t need to identify who they are. Planning for the shelters is mostly done. Camp layouts have been presented, and are up for argument. Logistics are coming along, but there is a lot to discuss: how much testing of equipment is required, where should it take place, and how do we get the materials from that place to Cape Town in an efficient manner?

For the past few weeks, the satellite link has been worrisome. Although there are two satellites which may be “visible” from Heard Island (in the radio sense, not the optical), they were not very high above the horizon. With terrain being significant on the island (camp is in a valley), and potential for local weather—especially low-layer marine weather—to negatively affect the satellite radio link, we were concerned that there would not be reliable data/phone connection from the island. Our expedition relies on that data link for safety, to keep in touch with off-island expedition headquarters, as well as to help the VK0EK ham radio operations with real-time contact reporting.

Fortunately, while discussing the expedition with satellite service providers, our satellite team found that one of the satellites in the constellation has been repositioned over the Indian Ocean. We will now have a satellite quite high in the sky, and communications are likely to be reliable. Bandwidth may not be very high still, but it’s better than from Pluto.

I’ve been doing some things for the expedition recently, too. Our Bay Area team has acquired laptops which will be used for the radio operation, and I have been helping with software configuration specifications for that. I have also been involved in radio team discussions about how to set up these portable stations—as an apartment-dweller, I know some things about setting up and tearing down stations. Simpler is better, as are plans with fewer moving parts (and less to haul on and off the island).

Last month, I tweeted a live Q&A session, discussing some of the science that has been done (or is proposed) on Heard Island. Check out the hashtag #HeardQuestions for that, and keep an eye out for another Q&A sometime (in a few months).

My physical training continues as well. I’ve been running, biking a little, doing core strength exercises, and stretching a lot more. Yesterday I was even convinced to take part in a 5k run. It has been several years since I last ran a 5k race, and while I’m not in the shape I was ten years ago, I definitely achieved my goals.

With seven months to go, I’m feeling really good about this expedition. Here’s hoping it comes off that well!

Compton Glacier Calving Seen from Space

Heard Island on a clear morning, seen by the MODIS instrument on NASA’s Terra satellite. July 31, 2015. Image credit: NASA GSFC (Terra/MODIS).

July 31st was a remarkable day on Heard Island, for several reasons. First, the weather was clear—a rare event in itself. Second, both NASA’s Terra and Aqua satellites had Heard Island reasonably near the center of their swath images. That’s not super-rare, but it’s probably <25%. Third, not only was the weather clear, but it was clear for both satellite overpasses, so both Terra and Aqua had good views of the island.

Many days, as I check the satellite images to see if Heard Island is visible, I end up playing “where in this image is Heard Island”. Imagine my surprise when I saw the Terra MODIS preview image from the morning pass, and there was a nice, bright white spot with some swirling grey vortices pointing toward it. The full-resolution image is shown above (cropped). It’s exactly the charismatic image I watch for, even though the resolution is moderate.*

I scrolled down the page to the Aqua MODIS images, which come from the early afternoon. Although Heard Island was a little off to the side of the image, leading to some artifacts, it was still free of the usual obscuring clouds. What a day! Two great images from when the island was within the usable part of the MODIS swaths.

Heard Island, standing in stark contrast to the dark blue waters of the Indian Ocean, on the afternoon of July 31, 2015 as seen by NASA’s Aqua satellite. Image credit: NASA GSFC (Aqua/MODIS).

As I looked more closely, I noticed something odd about the afternoon image: Compton Lagoon, in the northeast corner of the island, had a very odd shape. Usually it looks rather like it does in this map from the Australian Antarctic Division:

Topographic map of Heard Island, published July, 1999. Compton Lagoon is prominent in the northeast. Image Credit: Australian Antarctic Division.

Let’s look more closely at the satellite images.

Heard Island, morning of July 31, 2015. (Terra MODIS, as above; annotations mine).

Heard Island, afternoon of July 31, 2015. (Image from Aqua MODIS, as above; annotations mine).

Some of the difference between images comes from the North Barrier ridge, which runs from high up the volcano down to the west of Compton Lagoon, bounding the Compton Glacier to the northwest. With the sun in the northeast in the morning and northwest in the afternoon, the ridge stands out much more in the afternoon when it casts a shadow on the light glacier.

The lagoon, however, is quite different. Much of what was blue lagoon in the morning is grey in the afternoon, and the glacier seems to be a bit darker grey near its toe. I interpret that as evidence for a significant calving event, where ice, snow, and rocks from the glacier break off and slide/fall into the lagoon. A wind from the northeast (evidenced by the clouds) helps to keep the floating ice toward the west end of the lagoon.

Of course, it would be nice to have a second image showing the ice floating around in the lagoon, or a higher resolution image of the glacier. Unfortunately, since these images were taken, the images have been cloudy and/or off to the side of the field where distortion and artifacts are at their worst. I was hoping that the EO-1 satellite or Landsat 8 would get a good image with their 30 m resolution, but that doesn’t seem to be the case. That just goes to highlight how incredible these images are!

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* That’s the MOD in MODIS, the MODerate resolution Imaging Spectroradiometer; at its best (directly beneath the satellite) the resolution is 250 m/pixel.