In WOGE #595, Ole took us to Easter Island, figuring that it may take a while for it to be found! It would have taken me much longer to find had Felix not remarked about how it was a little early for that place!
Now for WOGE 596, we leave the volcanic cones behind.
Find the location, and leave a comment describing the important geology/hydrology/etc. of the scene. The person to leave the first correct location/comment gets to host the next WOGE.
Update: I neglected to mention that hints on searching, rules for hosting WOGE, and previous WOGE locations (.kmz) are available from Felix.
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.
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.
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.
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.
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.
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.
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.
Heard Island is a pretty cloudy place most of the time. However, there are occasional times when the weather clears, particularly on the southeastern (leeward) side of the island. On rare occasions, the northwest and southwest sides of the island come out from the clouds as a satellite passes over.
For the past two years, I have been watching Heard Island using true-color imagery from four satellites: Terra, Aqua, Landsat 8, and EO-1. I have postedpreviously about satellite imageryfrom these instruments. Although every image of the Island I have seen has clouds in it covering a portion of the island, I was curious whether or not I had accumulated clear imagery of the entirety of Heard Island.
In part, this question was spurred by a follower on Twitter asking about eruptive activity at Heard. I had to admit I didn’t really know whether the activity was low-level and continuous (like Kilauea) or more intermittent. Given that our knowledge of its eruptive activity is primarily from satellite observations, do the satellite “thermal anomalies” correspond to short eruptive events, or simply a cloud-free view of the volcano?
For high-resolution imagery of Heard Island, the datasets of interest are from EO-1 ALI, and Landsat 8 OLI. The two MODIS instruments (one on Aqua, one on Terra) are moderate-resolution, and while 250-m resolution is sufficient for some purposes, this one needs more. Looking through the archives, I was able to find EO-1 ALI data primarily for Mawson Peak and points southeast, and Landsat 8 OLI covered much of the island, particularly the northwest.
Not only is having cloud-free, high-resolution data important for me, but I want the data to be recent. There has been a retreat of up to 5.5 km for some of the glaciers since 1947, and the Google Maps imagery of that area (Stephenson Lagoon) is horribly outdated. Fortunately, I found most of the island covered in large swaths with images from 2014 onward, and mostly 2016. There was even good imagery from when I was on Heard Island! Our ship, the Braveheart, is visible as a few white pixels in Atlas Roads (just north of Atlas Cove), slightly closer to the Azorella Peninsula than to the Laurens Peninsula. The tents and campsite are too small and darkly colored to be visible on this image.
A small portion of the island between Atlas Cove and Mawson Peak was the most difficult to find. With the topography of the island, the steady stream of wind, and the humid air, the 2.5 km by 2.5 km region was cloudy pretty much all the time. Eventually, using the EO-1 ALI instrument and going back to early 2010, I found a reasonably clear image of it.
Once I had the images (after combining true-color and panchromatic brightness data in QGIS), I needed to stitch them together. Thanks to the wonderful QGIS training manual, I was able to create vector (polygon) layers which corresponded to the clear region of each image (plus some surrounding ocean). At this point the troublesome mostly-cloudy spot became evident, and the search was on for imagery to fill the void.
Finally, I tried to put them together. This turned out to be more trouble than it was worth for my purposes, having only five images. Several of the images had differing resolutions (10 m/pixel for EO-1 ALI, 15 m/pixel for Landsat 8 OLI). Additionally, since I was handling these in their raw format, color balances/exposures were not consistent across images. I decided it best, then, to leave them separate, and sent them around to the Heard Island Expedition team.
Soon I had an email from the expedition leader: he was very interested in the imagery, but it wasn’t opening in Google Earth. Some searching later, I found that Google Earth works best with a certain map projection (EPSG:4326), and when exporting the GeoTIFF, I needed to select “rendered image” rather than “raw data”. I re-exported the images, zipped them up, and tested it out on another computer: success! This Google Earth friendly imagery is now available here (17 MB zip).
One continuation of this project would be to keep looking through the documentation on GeoTiffs to find out how to make the rendered images use a transparent, not white, border where there is no data. That would likely let me create a virtual raster catalog to load all of them in one go, rather than having to load them separately.
About ten months ago, the Heard Island Expedition team launched the first of our eleven Argo buoys into the Indian Ocean. The buoys are equipped with conductivity-temperature-depth (CTD) instruments, and spend most of their time drifting about 1 km beneath the ocean surface. Every ten days, they dive to 2 km, then record CTD data as they ascend to the surface. At the surface, they relay the data via satellite over the course of a day before returning to 1 km depth. With a large network of these buoys, scientists can gather important data on currents under the ocean, as well as changes in temperature and salinity profiles.
Over time, ocean currents move the buoys. None of our eleven buoys are where they started, and some have moved far away from where they entered the ocean. We deployed two batches of buoys: six before reaching Heard Island from Cape Town, and five more on our voyage on to Fremantle/Perth.
I have obtained the latest position data (as of Jan 14, 2017) for the eleven buoys. Their tracks are shown in the figure at the top of this post. Tracks are colored by buoy, reusing the colors for the first and second batch. Some of the buoys have moved more than 1500 km as the albatross flies, with path lengths approaching 3000 km!
The CTD data are also interesting. For instance, here are the temperature/depth and salinity/depth profiles measured by buoy 5902454 (dark blue path on second leg of map above).
Around December 1, buoy 5902454 encountered a different water mass with colder, saltier water throughout much of the 2 km water column.
Generally for these buoys, the surface water temperatures reflect the seasonal variations (warmer in Austral summer, colder in winter), while the deep water shows less variation—but sometimes there are shifts between different water masses.
Heard Island is home to a spectacular outcrop. It’s the coolest outcrop I’ve ever seen, besting the Bishop Tuff tablelands, the potholes along the St. Croix River at Taylor’s Falls, Zion Canyon, The Badlands, and various outcrops in Yellowstone and Grand Teton. Admittedly this outcrop doesn’t intrinsically have the scale of many of the others just mentioned—it’s a roughly car-sized block—but the power that went into creating it and the effect it created is truly amazing.
On its face (see above), it looks quite pedestrian: a block of lithified glacial till with clasts of vesicular basalt reaching up to grapefruit size. However, it’s important to consider it from a different perspective.
When viewed from the side, a pile of sand in on the leeward (left, east) side of the block is evident. Additionally, the basaltic clasts of the rock face seem to be protecting the softer, tan-colored glacial matrix from the sand-blasting.
Here’s a close-up from an oblique angle:
In the oblique view, the volcanic clasts making up the face of the outcrop are seen sheltering the matrix directly to the leeward from mechanical erosion. To tie all of these views together, I took a short video (embedded below).
This outcrop is located on the edge of a volcanic sand plain roughly 1.5×1.5 km. Strong westerly winds are present most of the time (9 m/s is average, measured at a site nearby). In fact, the audio which accompanies the video is mostly wind noise, though there’s a little unintelligible chatter with my field partner, Carlos. Winds when the recording was made were “moderate” (for Heard Island) and from the west, exactly the kind of winds that shaped this outcrop. At the time of the recording, the winds weren’t strong enough to kick up much sand, nor were ice pellets falling from the sky, but on a gustier, stormier day, the face of this outcrop will take a beating.
In my travels and geo-adventures, I’ve seen differential weathering and ventifacts (outcrops shaped by wind), but never so strikingly combined as at this outcrop on Heard Island. That’s why I can confidently say it’s the coolest outcrop I’ve seen on Heard Island or anywhere else in the world.
 Thost, D., Allison, I. “The climate of Heard Island” in Heard Island: Southern Ocean Sentinel, ed by K. Green and E. Woehler. Surrey Beatty & Sons, Chipping Norton 2005, p. 52-68.