Tag Archives: Geoscience

AGU 2017, Day 5

Unlike some other years, this year I had a packed day of conferring on the last day. I started out in the posters, because one of the Heard Island presentations was there. On my way to the poster I came across one of the geology professors from my college, and I talked with him a bit about my research. It’s possible I will end up on their seminar schedule. Upon arriving at the poster I was looking for, I learned about the helium isotope composition of bubbles near Heard Island and the McDonald Islands: they’re relatively mantle-like by McDonald, and likely more methane-seeps by Heard.

From there it was on to the exhibit hall, to see a few friends from grad school and make sure I hadn’t missed anything too exciting at the booths. I checked out a few of the aeronomy posters (about Earth’s ionosphere) to see if I could find any good ideas for speakers at the amateur radio clubs I am now in leadership positions in.

Having had enough of the posters, I decided to go to the session on indigenous knowledge and climate change. It was a particularly interesting session, and I wish more of the conference attendees had been there.

Finally, it was time for lunch with a friend from grad school, then off to the airport to head home.

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AGU 2017, Day 3

What a day! I fortuitously came across quite a few people I know from either my undergraduate institution or my PhD work, and managed to catch up with some of them. I explored about a third of the exhibits in the exhibit hall, and learned about cool new instrumentation, including the Raspberry Shake.

In the afternoon, I went to a volcanology session about flood basalts and large igneous provinces, and it was riveting. Loyc Vanderkluysen is working on a new classification scheme for the Deccan Traps, which cover an area roughly the size of Texas and may have covered three times that area when they were first erupted. These lavas, found in modern-day India, have formation boundaries defined by their chemistry, but the choice of chemistry to use for classification and differentiation seems like it could be improved by modern data analysis techniques.

But the talk that really stood out was by Courtney Sprain, talking about dating the Deccan Traps. Papers published in 2015, one using U/Pb dating (Schoene et al.) and the other using Ar/Ar dating (Renne et al.), concluded that the Deccan Traps were erupted almost entirely between 67 Ma (Mega-annum, million years ago) and 65 Ma, right across the Cretaceous-Paleogene (K-Pg) boundary. However, the middle portion of the sequence was not dated sufficiently precisely to test whether the Chixulub impact caused increased volcanism in the Deccan Traps. In this new work, many additional samples have been analyzed with high-precision Ar/Ar using many multi-grain step-heating experiments. As a result, the data are now sufficient to test whether volcanism changed or increased at the same time as the impact. The K-Pg boundary occurs right at an important formation boundary, and Nd isotopes shift there (toward less crust-like, more mantle-like ratios) as well. Feeder dikes, which lower in the sequence were generally oriented in one direction, became randomly oriented above the chronological boundary.

All of which is to say, the new data are of a quality where it would be possible to falsify the hypothesis that the impact caused increased volcanism, but they do not falsify that hypothesis. Indeed, they are quite consistent with it. Wow!

Claims of impact-triggered flood basalts are rather radical, and need some solid data to back them up. The speakers in these sessions were clear to say that this isn’t by any means sufficient yet to declare the new paradigm accepted and move on. Still, this was a pretty big test of the hypothesis, and it came through unscathed.

In the morning, I will be presenting my poster on the retreat of Stephenson Glacier, Heard Island (poster C41B-1222). This conference has been keeping me very busy, and it looks like that will continue through the time I leave. I’m very excited about what I’ve been learning, the people I’ve been talking with, and the ideas that are coming together as a result of this conference. The long conference center (it’s nearly 1 km end-to-end) is keeping me in good shape, too!

Heard Island Landslide!

Landslide on Compton Glacier, Heard Island, 2017-07-21.  Image credit: processed by Bill Mitchell (CC-BY), using USGS/Landsat 8 data.
Landslide on Compton Glacier, Heard Island, 2017-07-21. Image credit: processed by Bill Mitchell (CC-BY), using USGS/Landsat 8 data.

On July 21, 2017, the Landsat 8 satellite imaged a fresh landslide on Heard Island, seen in the picture above. The slide occurred in the northeast portion of the island, on top of Compton Glacier, and I have annotated it for clarity in the image below.

Satellite image of Heard Island with annotation marking the region where the landslide is present.  Image credit: processing and annotation by Bill Mitchell (CC-BY), data from USGS/Landsat 8.
Satellite image of Heard Island with annotation marking the region where the landslide is present. Image credit: processing and annotation by Bill Mitchell (CC-BY), data from USGS/Landsat 8.

This landslide is quite easy to spot because of the relatively clear conditions over Heard Island and the very high contrast between the dark, presumably-basaltic rocks and the white snow of the glaciers. Given that it is presently austral winter and Heard Island is located south of the Antarctic Convergence, the rate of snow accumulation should be quite high. It will be interesting to see how long it takes to be covered by snow.

I am fairly convinced that this is a rock- or landslide rather than an eruption. The head of the flow is along the top of a steep ridge, and the infrared imagery shows no thermal anomaly in this part of the island.

What’s interesting to me is that this slide appears to have eroded some snow on top of the glacier which then caused a secondary avalanche from a north-facing slope. I’ve annotated this in the image below.

Region of secondary avalanche.  Image processing and annotation: Bill Mitchell (CC-BY), data from USGS/Landsat 8.
Region of secondary avalanche. Image processing and annotation: Bill Mitchell (CC-BY), data from USGS/Landsat 8.

This landslide has a run-out of about 2.5 km, an elevation drop of ~750 m, and a total affected area of ~0.8 km2. Several flow tongues are evident in the close-up image, even though the satellite imagery resolution is a modest 15 m/pixel.

Close-up of landslide on Compton Glacier, Heard Island.  Several flow paths of dark rock are evident here.  Image processing: Bill Mitchell (CC-BY), data from USGS/Landsat 8.
Close-up of landslide on Compton Glacier, Heard Island. Several flow paths of dark rock are evident here. Image processing: Bill Mitchell (CC-BY), data from USGS/Landsat 8.

From this image, it looks like the rockfall mostly happened in the portion running west-to-east, then as it turned the corner to head northeast, transitioned to a surface flow. In many ways, this reminds me of the Mt. Dixon (New Zealand) rock avalanche in 2013 (coverage by Dave Petley here and here, among others). The video below is from the Mt. Dixon (NZ) rock avalanche, but is likely similar to what occurred on Heard Island.

A fly-over after the Mt. Dixon (NZ) rock avalanche provided more video of the rock avalanche scar.

I look forward to seeing more images of this slide as they come in. Heard Island is imaged roughly every 8 days by Landsat 8, which as far as I can tell is the only publicly available high-resolution imagery for the island now that EO-1 has been decommissioned.

Capitol Rock Close-Up

Close-up outcrop photograph of Capitol Rock, viewed from the north-northeast.  Image credit: Bill Mitchell (CC-BY).
Close-up outcrop photograph of Capitol Rock, viewed from the north-northeast. Image credit: Bill Mitchell (CC-BY).

Two years ago, I came tantalizingly close to Capitol Rock, an outcrop in southeastern Montana (45.572189, -104.087964) just a few miles over the border from Camp Crook, SD. Unfortunately, I did not have an opportunity at that time to explore the outcrop from any closer than about a quarter mile, but I did find the Ekalaka Quadrangle 30’x60′ (pdf) geologic map.

Recently, I was out in the area again, and this time made sure to have time to take some pictures and see some of what was to be seen. Let’s start with the quarter-mile view, which is roughly equivalent to what I saw last year.

Wide view of Capitol Rock from the east.  Image credit: Bill Mitchell (CC-BY).
Wide view of Capitol Rock from the east. Image credit: Bill Mitchell (CC-BY).

Capitol Rock has three major parts to it: an easily eroded base, a laminated sandstone middle, and a massive sandstone top. A handy turn-out from the forest service road leads right to the base of the outcrop.

The easily eroded base is made of fine, chalky, white sediment sediment, and it remains in horizontal orientation. In several places, this unit is at least superficially porous. Surprisingly, there are occasional chert clasts in the otherwise fine sediments—I’m not quite sure how those would have been deposited or formed here.

Basal unit of Capitol Rock.  Foot for scale.  Image credit: Bill Mitchell (CC-BY).
Basal unit of Capitol Rock. Foot for scale. Image credit: Bill Mitchell (CC-BY).
Cherty clast in the basal sediments at Capitol Rock.  Foot for scale.  Image credit: Bill Mitchell (CC-BY).
Chert clast embedded in the basal sediments at Capitol Rock. Foot for scale. Image credit: Bill Mitchell (CC-BY).

Above the basal unit is a somewhat more resistant, coarser-grained set of beds. These strata are finely bedded, and have a tendency toward spheroidal weathering. Occasionally interbedded with the spheroidal beds are 1–3 cm thick, well-cemented strata of a white or pink color [discoloration?].

Spheroidal weathering of finely-laminated strata.  Hand for scale.  Image credit: Bill Mitchell (CC-BY).
Spheroidal weathering of finely-laminated strata. Hand for scale. Image credit: Bill Mitchell (CC-BY).
Laminations in the unit displaying spheroidal weathering.  Hand for scale.  Image credit: Bill Mitchell (CC-BY).
Laminations in the unit displaying spheroidal weathering. Hand for scale. Image credit: Bill Mitchell (CC-BY).
Non-spheroidal bed 1–3 cm thick and slightly orange-pink in coloration, within the spheroidal beds at Capitol Rock.  Hand for scale.  Image credit: Bill Mitchell (CC-BY).
Non-spheroidal bed 1–3 cm thick and slightly orange-pink in coloration, within the spheroidal beds at Capitol Rock. Hand for scale. Image credit: Bill Mitchell (CC-BY).

The spheroidally-weathered unit also seems to have one or more channels within it.

Contact between spheroidally-weathered strata (above) and easily-weathered basal unit (below).  Possible channel cut at right.  Outcrop height in image is ~10 m.  Image credit: Bill Mitchell (CC-BY).
Contact between spheroidally-weathered strata (above) and easily-weathered basal unit (below). Possible channel cut at right. Outcrop height in image is ~10 m. Image credit: Bill Mitchell (CC-BY).
Contact between spheroidally-weathered strata (above) and easily-weathered basal unit (below).  Possible channel cut at right has been annotated.  Outcrop height in image is ~10 m.  Image credit: Bill Mitchell (CC-BY).
Contact between spheroidally-weathered strata (above) and easily-weathered basal unit (below). Possible channel cut at right has been annotated. Outcrop height in image is ~10 m. Image credit: Bill Mitchell (CC-BY).

The upper unit at Capitol Rock has more massive sandstone (see wide view above). I didn’t notice many channels in this unit, although I didn’t get very close. A butte just to the north of Capitol Rock provided a good photograph (below).

Massive unit of Capitol Rock, seen in the butte immediately to the north of Capitol Rock.  Cliff is ~30–40 m tall.  Image credit: Bill Mitchell (CC-BY).
Massive unit of Capitol Rock, seen in the butte immediately to the north of Capitol Rock. Cliff is ~30–40 m tall. Image credit: Bill Mitchell (CC-BY).

Although I have those observations, I don’t have much for interpretation of them. The depositional environment seems to be relatively low-energy (give or take the chert clasts), evidenced by the flat strata, fine grain sizes, and relatively few cross-beds. Changes in the rock types would suggest changes in the sediment sources or the depositional environment (or both). There may be post-deposition alteration effects as well, such as cementation of the spheroidally-weathering strata.

View SSE from the butte just north of Capitol Rock.  Truck for scale in pull-out near Capitol Rock.  Image credit: Bill Mitchell (CC-BY).
View SSE from the butte just north of Capitol Rock. Truck for scale in pull-out near Capitol Rock. Image credit: Bill Mitchell (CC-BY).

Capitol Rock is an interesting outcrop, and if you’re in the area, I’d recommend a stop. The rocks are interesting, there are US Forest Service campgrounds nearby, and the view is quite nice. These units can probably be correlated to the Slim Buttes in South Dakota (~45 miles east).

Nares Glacier to Mount Drygalski Panorama

Panorama from Nares Glacier (left) to Mt. Drygalski (right) from the Atlas Cove camp.  This view spans from ESE through SSW, and is roughly 85 megapixels at full size.  Image credit: Bill Mitchell (CC-BY, hosted on flickr).
Panorama from Nares Glacier (left) to Mt. Drygalski (right) from the Atlas Cove camp. This view spans from ESE through SSW, and is roughly 85 megapixels at full size (28 MB). Image credit: Bill Mitchell (CC-BY, hosted on flickr).

One year ago, I was on Heard Island. Over the course of the expedition I took more than 6000 photos. Although I took three images with the Gigapan (Big Ben, the Azorella Peninsula, and—my favorite—Windy City), I also took photos for stitching together manually using my own camera.

I have been slow in stitching these pictures together, but with the one-year anniversary of their production coming around, I decided it was time to finish one or two of them. This is the first, and I hope I’ll find time to finish more. Putting it together, I was amazed that this is still a relatively wide-angle compared to what I had available: 70 mm on a 70–200 mm lens. The detail came out well, as is evident at full-size. The glaciers, moraines, and hills are all more than a kilometer distant over the “nullarbor”, a broad, flat, volcanic-sand plain.

Toward the left half of the image are some penguins for scale. They look like king penguins, putting their height around 1 meter. I count at least 31 penguins in the entire image.

I think I spot some of the relatively rare basement limestones cropping out at the very left edge of the image, and their appearance is consistent with a dip of 25–35° to the south.[1] A closer view (200 mm focal length) shows them more clearly.

Location of limestone, with annotation.  Image credit: Bill Mitchell (CC-BY).
Location of limestone, with annotation. Image credit: Bill Mitchell (CC-BY).
Full-zoom on the limestone outcrop.  Bedding is clearly visible, dipping south.  Image credit: Bill Mitchell (CC-BY).
Full-zoom on the limestone outcrop. Bedding is clearly visible, dipping south. Image credit: Bill Mitchell (CC-BY).

[1] 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.

Big Ben Eruption Update 2017-02-27

Mawson Peak's summit crater glows orange in this false-color infrared image (bands 7-6-5) taken February 27, 2017.  Image credit: Bill Mitchell (CC-BY) using data from USGS LANDSAT 8 (public domain).
Mawson Peak’s summit crater glows orange in this false-color infrared image (bands 7-6-5) taken February 27, 2017. Image credit: Bill Mitchell (CC-BY) using data from USGS LANDSAT 8 (public domain).

It has been three weeks since I reported on an active eruption on Heard Island seen by Landsat 8. Since then, the presence of lava at or near the surface in the summit crater of Mawson Peak has continued, and a thermal anomaly is present both in the February 27 Landsat 8 image shown above and in February 20 imagery. It is difficult to discern in the true-color imagery from February 27 whether there are any new lava/debris flows present. The two MODIS instruments (one on Aqua, one on Terra) have not picked up any thermal anomalies since early February.

Unfortunately, one of the best tools I’ve had at my disposal for keeping an eye on Mawson Peak is no longer available: NASA/USGS satellite EO-1 was decomissioned last week. EO-1 provided 10 m/pixel true-color imagery, which is significantly higher resolution than 15 m/pixel of Landsat. Archival data for both satellites remains available, but no new EO-1 data will be taken. New data from Landsat 8 typically comes in a few times each month (every 7-16 days), and I’ll be keeping an eye on it.

Mawson Peak in true color, February 27, 2017.  Image processing: Bill Mitchell (CC-BY) using USGS Landsat 8 data (public domain).
Mawson Peak in true color, February 27, 2017. Image processing: Bill Mitchell (CC-BY) using USGS Landsat 8 data (public domain).

Big Ben Eruption, 2017-02-04

Lava and debris flows radiate away from Mawson Peak on Heard Island.   February 4, 2017.  Image credit: Bill Mitchell (CC-BY) using data from Landsat 8 OLI (NASA/USGS; public domain).
Lava and debris flows radiate away from Mawson Peak on Heard Island. February 4, 2017. Image credit: Bill Mitchell (CC-BY) using data from Landsat 8 OLI (NASA/USGS; public domain).

On February 4th, Landsat 8 captured a clear view of the summit of Big Ben volcano, at Heard Island. Heard Island is a very cloudy location, so clear views are uncommon (I don’t have numbers, but would estimate <20%). However, the February 4th images are even more spectacular: they capture an ongoing volcanic eruption.

Observations
In the sharpened true-color image (above), four or five different lava/rock/debris flows are visible emanating from the summit. Using a false-color infrared image (below), two hot regions are apparent (red/orange/yellow), and are separated by about 250 meters. The longest of the flows stretches nearly 2 km, and drops from an elevation of roughly 2740 m to 1480 m (using 2002 Radarsat elevation data with 20 m contours). All three of the large flows to the west or southwest of the summit drop below 2000 m elevation at the toe.

False-color infrared imagery of Mawson Peak, Heard Island.  Two vents are visible in red/orange/yellow, separated by 250 meters. Data source: Landsat 8 OLI/TIRS bands 7-6-5.  Image credit: Bill Mitchell (CC-BY), data from NASA/USGS (public domain).
False-color infrared imagery of Mawson Peak, Heard Island. Two vents are visible in red/orange/yellow, separated by 250 meters. Data source: Landsat 8 OLI/TIRS bands 7-6-5. Image credit: Bill Mitchell (CC-BY), data from NASA/USGS (public domain).

Interpretation
In the sharpened true-color imagery, I have identified five rock and debris flows originating at the summit, as well as one potential avalanche. Annotation of these observations is found on the pictures below.

Annotation of lava/rock/debris flows from Mawson Peak, Heard Island, February 4, 2017.  Image credit: Bill Mitchell (CC-BY).
Annotation of lava/rock/debris flows from Mawson Peak, Heard Island, February 4, 2017. Image credit: Bill Mitchell (CC-BY).

The streaky, varying lightness of the flow areas, presence of snow and ice, and steep terrain lead me to believe that what is showing up here are mixed snow/rock/lava debris flows, rather than pure lava flows. A mix of rocky debris and snow would not be out of line for a supraglacial eruption on a steep mountain. The longest flow drops nearly 1300 m along its 2000 m horizontal path according to the 2002 Radarsat elevations. I’ll be the first to admit that I am distrustful of the specifics of the Radarsat contours due to the rapidly changing landscape and an intervening 15 years, but I think that it manges to get the general picture right.

Southwestern Heard Island is a high-precipitation area, so rocks exposed on the surface of the glaciers are likely quite fresh. It probably won’t be long before most of the deposits are covered in snow again.

Speaking of snow, it looks as though there is a faint outline of an avalanche scarp/deposit on the northeast side of the summit, which I annotated below in green.

Annotation of avalanche scarp and deposit, Mawson Peak, Heard Island, February 4, 2017.  Image credit: Bill Mitchell (CC-BY)
Annotation of avalanche scarp and deposit, Mawson Peak, Heard Island, February 4, 2017. Image credit: Bill Mitchell (CC-BY)

The two hot spots provide an interesting challenge for interpretation. Two scenarios come to mind quickly: there are two vents from which lava is issuing, or there is a lava tunnel from a summit crater down to a flow front or breakout. Analyzing the Landsat 8 OLI/TIRS infrared imagery from January 26th (most recent previous high-resolution image), only one hot spot is present—in the same place as the eastern hot spot in the February 4th infrared image. For spatial correlation without doing the whole image processing and GIS thing, use the forked flow to the south-southeast of the hotspot as a reference.

False-color infrared image of Mawson Peak, January 26, 2017.  Landsat 8 OLI/TIRS bands 7-6-5.  Image credit: Bill Mitchell (CC-BY) using NASA/USGS data (public domain).
False-color infrared image of Mawson Peak, January 26, 2017. Landsat 8 OLI/TIRS bands 7-6-5. Image credit: Bill Mitchell (CC-BY) using NASA/USGS data (public domain).

Due to a different time of day for imaging, there are significant shadows in the January image on the southwest side of ridges. It’s tricky to figure out what is going on for the flows (even in visible imagery), but the hot spot from January 26th is right on top of the eastern hot spot from February 4th.

Another thing which becomes apparent in the January image is the topography at the summit. The clouds form a blanket at an atmospheric boundary (and roughly-constant elevation), which is conveniently just below the elevation of the summit. A roughly circular hole in the clouds is present, and a conical mountain summit pokes through with the hot spot right in the center. That suggests that the second hot spot seen in the February 4th image is at a lower elevation—a possible flow front or breakout.

Excitement in the Mundane
Finding this eruption was a bit of a surprise to me: the low-resolution preview image for the Landsat data on EarthExplorer was so coarse that there wasn’t anything striking or out of the ordinary visible at the summit. Clouds covered most of the rest of the island. However, when I opened up the full-resolution color images (30 m/pixel), it was immediately evident that this was a special day. Sharpening the true-color bands with the high-resolution panchromatic band using QGIS made it pop all the more!

Upon seeing both the lava/debris flows and the thermal anomaly, I checked the MODIS volcanism (MODVOLC) site to see if the Terra and Aqua MODIS instruments had picked up thermal anomalies as well over the preceding week. They had, as shown below. Both satellites had recorded thermal anomalies at Heard on February 2nd and 3rd.

MODIS thermal events at Heard Island, in the week preceding February 6, 2017.  Image credit: MODVOLC.
MODIS thermal events at Heard Island, in the week preceding February 6, 2017. Image credit: MODVOLC.

Update:: Follow-up from February 27, 2017.