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.
This post is the first in a series of three on the gigapans I took on Heard Island. (Part 2, Part 3)
My first gigapan on Heard Island, this one of Big Ben, came unexpectedly. As I was out hiking one afternoon, my hiking partner, Arliss, noticed that we had a clear view of the summit of Big Ben. Clearings like this can be relatively short and infrequent, so we took a few pictures immediately. We headed back to base camp just east of Atlas Cove, arriving under an hour before sunset. The mountain was still visible, so I moved quickly to set everything up and get the gigapan taken before the light faded.
From camp, Big Ben is situated to the southeast, rising up beyond the flat sandy plain of the nullarbor. In this view, the moraines and glaciers begin about 2 km from the camera. To the right of the image is the eastern slope of Mt. Drygalski. The edge of the Azorella Peninsula lava flow is in the bottom left corner.
Glacial features dominate the landscape, including a prominent moraine now covered in vegetation (lower right). Coming toward the camera are the Schmidt and Baudissin glaciers. I think this view covers from the Allison and Vahsel glaciers (at right) to the Ealey glacier (at left).
On the Nullarbor, there are a few king penguins and elephant seals, primarily to the left of center.
Big Ben itself has a range of rock types, including basanites, alkali basalts, and trachybasalts, overlying limestones and volcanic/glacial deposits.[1-4]
 Barling, J.; Goldstein, S. L. (1990) Extreme isotopic variations in Heard Island lavas and the nature of mantle reservoirs. Nature 348:59–62, doi 10.1038/348059a0.
 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 35:1017–1053, doi 10.1093/petrology/35.4.1017.
 Stephenson, J.; Barling, J.; Wheller, G.; Clarke, I. “The geology and volcanic geomorphology of Heard Island”, in Heard Island: Southern Ocean Sentinel (Eds K. Green and E. Woehler) Surrey Beatey & Sons, 2006, p. 10–27.
Heard Island is a pretty magical and dramatic place. I’ve been very busy with my IT duties, radio duties, and general camp upkeep. However, I’ve managed to take a few pictures in spare moments, and the highlights are posted here.
Previously, I wrote about some of the challenges of studying the mantle. I also wrote about mass spectrometers—this was not accidental, as they were used heavily in the research discussed here. If you have not read those items already, you should do so before continuing. Also, if you are not familiar with isotopes, you may wish to get more familiar with those as well.
Although Big Ben is the dominant feature on Heard Island (seen above with a bow wave and some poorly-defined Von Karman vortices), there is a smaller volcanic edifice, Mt. Dixon, on the Laurens Peninsula (to the NW, right in the bow wave from Big Ben). Mt. Dixon is home to many lava flows, which can be seen on Google Earth, and are believed to be as young as 200 years or less.
The major-element composition (Si, K, Na) of the lavas from Big Ben and Mt. Dixon can be quite different. Big Ben generally has basalt and trachybasalt composition (low SiO2, moderate K2O + Na2O), while the Mt. Dixon and the other cones on the Laurens Peninsula show a much wider range, from basanite to trachyte (wide range of SiO2, generally higher K2O + Na2O).
Where things really get interesting is in looking at the isotopes. Specifically, Barling et al. looked at the isotopes of Sr, Nd, and Pb isotopes.[2,3] Some of those isotopes (86Sr, 144Nd, and 204Pb) are stable and non-radiogenic. That is, they do not decay away, nor are they formed from radioactive decay. The other isotopes studied (87Sr, 143Nd, 206Pb, and 207Pb) all are stable, but are the products of radioactive decay (87Rb, 147Sm, 238U, and 235U, respectively).
The ratio of radiogenic/non-radiogenic isotopes can be used to identify different sources, sort of like fingerprinting. To get high concentrations of radiogenic isotopes means that the rock’s history includes lots of the radioactive parent. Low concentrations of radiogenic isotopes means that the source rock has relatively little of the radioactive parent.
This is important, because although isotopes of an element are chemically similar, different elements behave differently from a chemical standpoint. Some are more often found in the crust than the mantle, while others are the opposite, depending on the compatibility of the element in mantle minerals.* Uranium is generally incompatible, and preferentially moves into the continental crust. Crustal rocks, would be likely to have a high ratio of radiogenic to non-radiogenic lead (product of uranium decay). Mantle rocks would have a lower ratio of 206Pb/204Pb, and similarly for 207Pb/204Pb.
Zindler and Hart (1986) proposed that oceanic basalts can be treated as mixtures of four components, each having a distinct chemical (and isotopic) composition.[4, via 2] Barling and Goldstein found that the Heard Island lavas exhibit a range of compositions consistent with mixing between two sources. Neither of those sources matches the compositions suggested by Zindler and Hart. For the first Heard Island source, three explanations are given why that may be the case:
The Heard Island source is a mixture of two Zindler and Hart sources
That same Heard Island source is a fifth distinct mantle source
It’s more complicated; the two Zindler and Hart sources in question define a spectrum, and the Heard Island source lies along that spectrum
Barling and Goldstein (1990) favored case 3, which they argue is reasonable given that recycling continental crust is likely to give a wide range of isotopic compositions.
Barling et al. (1994) built off of the results presented by Barling and Goldstein (1990), and focused on two main questions:
First, what is the origin of continental crustal signatures in oceanic basalts; are they inherited from the mantle source region, or are they caused by shallow contamination? If they originate in the mantle, how much continental material is present, how is it distributed and in what form, and how and when did it become incorporated into the mantle? Second, what are the origin and timing of enrichment of the sub-Indian Ocean mantle?
Perhaps some clarification is needed about what is at issue. Since it is clear there is some continental influence expressed by the Heard Island lavas, where in the history of that magma did mixing with continental crust occur? Was there a chunk of intact continental material relatively near the surface which partially melted as the basalt came upward through it? Or was there continental material which has been mixed in to the mantle beneath the Indian Ocean? If that occurred, when, and under what conditions?
Their data, and particularly the lead isotopic data (207Pb, 206Pb, and 204Pb), lead them (pardon the pun) to conclude that the component with a high-87Sr/86Sr is derived from marine (ocean) sediments subducted into the mantle at least 600 Ma before present, and probably 1–2 Ga. Modeling of the Sr isotope ratios and total concentrations, along with thermodynamic considerations, suggest that partial melting followed by partial crystallization from the magma is unlikely. That is, recycled crustal material is needed to make things work.
Barling et al. (1994) found that the overall isotopic compositions of the lavas suggest, if crustal material is indeed being recycled into the mantle, the subduction occurred around 1–2 Ga. That timing makes it far too early to be related to subduction beneath the paleo-supercontinent Gondwana.
Finally, the paper closes with the suggestion that, although Heard Island and Kerguelen Island are separated by 440 km, the two may be manifestations of the same plume head and hotspot. They note that the distance between the islands is quite small for separate hotspots, yet is obviously large for being just one hotspot. Perhaps the 2015 Heard Island expedition can collect samples which will give insight into resolving this question.
 Barling, J.; Goldstein, S. L. (1990) Extreme isotopic variations in Heard Island lavas and the nature of mantle reservoirs. Nature 348:59-62, doi 10.1038/348059a0.
 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 35:1017-1053, doi 10.1093/petrology/35.4.1017.
* This turns out to be crucial for things like uranium-lead dating, where the mineral zircon generally crystallizes with 10-1000 ppm U, but does not incorporate Pb. All the Pb found in a zircon can be assumed to come from uranium decay or laboratory contamination (which has a known isotopic composition).
Heard Island is covered in interesting geology, with windows into the past, the present, and the Earth’s interior. In the coming weeks, I expect this will be a recurring topic, so if there are parts you’d like me to elaborate on, please leave a comment!
There are three main rock types on Heard Island: volcanic rocks, marine sediments, and increasingly, glacial sediments. We will focus primarily on the first two, as the glacial sediments are quite recent and not yet lithified, and less has been written about them.
At the base of the stratigraphic sequence accessible above sea level are marine sediments, specifically limestone. These sediments are composed of the carbonaceous shells of micro-organisms, and were deposited when the water was very shallow, but in an open-ocean setting. From the types of shells found, these limestones were deposited between about 60–30 million years ago (Ma).[1 and references therein] (Refresher on the geologic timescale)
Overlying the limestone is the Drygalski Formation, which is of volcanic origin, and begins around 10 Ma. The Drygalski formation includes pillows, which are small (<1 m diameter) blobs of rock which form when lava is erupted underwater, which rapidly cools the outsides.* Other rocks in this formation include hyaloclastite, which is also characteristic of submarine volcanism. Glacial sediments in the form of tillite (wide range of sizes of sediment with clasts (rock chunks) supported by much finer grain sizes) are also present in this formation, indicating the presence of glaciers in the area.
Volcanism has begun again more recently, no later than about 1 Ma (based on K-Ar dating), and created the modern volcanic structures on the Laurens Peninsula and Big Ben itself. This volcanism continues in the present-day, and eruptions have been observed by satellite in 2013 (see picture above). Not only are there the volcanoes of the Laurens Peninsula and Mawson Peak atop Big Ben, but there are numerous small volcanic cones along the perimeter of the island. The age of these cones is unknown, but their small size and fresh appearance suggest they are quite recent (100-5000 years?).
Dr. Will Powell of Macquarie University has a number of good field photos from a trip to Heard Island in 2000, as well as a bit of commentary to go along with them. One of the pictures is of a basaltic dike intruding rocks on the north end of the Laurens Peninsula. That dike is where magma squeezed up from below, possibly to a surface eruption above which may have been subsequently eroded away.
Finally, Heard Island has glacial sediments (till). This is being deposited in the lagoons and on the land as the glaciers retreat. I expect to find medial and terminal moraines when I am there, and some of the moraines are presently visible in the satellite imagery. There is a terminal moraine (or is it a ground moraine?) at the end of the glacier in the upper right of the picture above, at around the 2:00 position in relation to Big Ben. It is manifested as a brown patch between the glacier and the lagoon.
So, that’s the brief overview of the rocks of Heard Island. All the rocks are from the Cenozoic (<66 Ma), with the oldest being limestones, then some much younger volcanics and glacial sediments on top, with both the volcanics and glacial sediments depositing presently. I can’t wait to get there and see them in person!
 Clarke, I., McDougall, I. & Whitford, D.J., 1983: Volcanic evolution of Heard and McDonald Islands, southern
Indian Ocean. In Oliver, R.L., James, P.R. & Jago, J.B. (Eds): ANTARCTIC EARTH SCIENCE. Australian Academy of Science, Canberra: 631-635.