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!
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.
Today there is a new video out from scientists aboard the R/V Investigator which shows a volcanic eruption occurring from Mawson Peak, Heard Island. This is an exciting video not because it is unusual for an eruption to happen on Heard Island—the Global Volcanism Program shows activity on about an annual basis for the last few years—but because it is unusual for someone to be there to see it!
In the video above, a small plume can be seen over Mawson Peak, and a few lava flows. Given the terrain near the summit and the imagery below from lava flows in 2013, I think it is safe to say that the flows are heading down the southwest flank. As someone going to this island in less than two months, the direction of lava flows is important: it is away from the campsites which we intend to use.
From the video above, this appears to be an effusive eruption, where lavas gently flow out of the volcano. That eruptive style is consistent with a hot (~1100 °C), basaltic (low-SiO2) melt—eruptions with a high SiO2 content tend to have cooler lava and are more often explosive in nature. Basalts or other lavas (trachybasalts and basanites) with low SiO2 (48–52%) are typical of the Big Ben series of lavas (Big Ben being the volcano upon which Mawson Peak is located). Predicting that the lavas from this eruption would be generally low-SiO2 seems fairly safe, although our expedition is not equipped to undertake the sampling required to test that prediction.
 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.
On a conference call some weeks ago, Nigel Jolly, captain of the RV Braveheart which will be taking the Heard Island expedition to Heard Island in March and April, 2016, told the expedition members that they will be expected to be in good physical shape for this expedition. Specifically, he reminded us that not only will we need to be able to walk around on the uneven and slippery ground, but that we will need to do so while carrying heavy things (potentially fragile and expensive, and generally needed for a successful expedition). In order to prepare ourselves, we are to get out and try walking around with heavy stuff on uneven ground.
Naturally, my first thought was that he just told me I needed to go backpacking on the north shore of Lake Superior. Don’t twist my arm too hard!
I called my cousin, who I figured would also probably need some arm-twisting to go backpacking on the North Shore, and we figured out the logistics. We even managed to reserve a hike-in campsite in Split Rock State Park that was right along the shore. Before we left, I checked through Roadside Geology of Minnesota to see if there were any special features besides the anorthosite (rock almost exclusively made of the mineral anorthite, which is a feldspar) which makes up Split Rock itself, and I put a few places on the quick stop list for the drive home.
The geology along the Split Rock River did not disappoint. Here were lava flows, more than a billion years old (1 Ga). Along the river channel, columnar jointing was often evident (see the far bank of the cascade and the far canyon wall above). Most of the lava flows were massive. The opposite canyon wall in the photograph shows columns 5–10 m tall, which would have formed in a single flow. That’s a lot of lava! While hiking along, I was on the lookout for ropey pahoehoe flow-tops, but did not find any that I recognized.
Lava flows found along the North Shore are generally part of the North Shore Volcanic Group, and have an age of roughly 1.1 Ga. They were formed as part of the Mid-Continent Rift system, and now dip gently (~20°) toward the lake. Many of the flows are basalts (low silica, high iron), although there are rhyolites (high silica, low iron) in the area (such as Iona’s Beach).
It was fun to get to see some igneous rocks up close in outcrop (I live on a lot of glacial sediments, and the bedrock is Paleozoic sediments). The backpacking definitely demonstrated that more such activities are needed, because my legs were quite sore by the end of the hiking and the next few days. However, we did have a gorgeous view from the campsite! In the photo below, you can see the gentle dip of the lava flows toward the lake. Obviously, the weather we had on the North Shore (quite comfortable!) was much, much better than is expected for Heard Island. I had a great trip, and hope to head back up some time for more hiking adventures.
Nicholson, S.W., Cannon, W.F., and Schulz, K.J., 1992, Metallogeny of the midcontinent rift system of North America: Precambrian Research, 58 (1-4), p. 355-386. DOI: 10.1016/0301-9268(92)90125-8
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).
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.
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, ). 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.
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.
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
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.
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.
 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.
When you need to make something really hot—1350 °C—a tilt furnace can be a great tool. This is especially true if you are an experimental volcanologist. At Syracuse University, faculty in the geoscience and art departments have teamed up to make actual lava flows on a small scale.
One of the major risks in studying volcanoes is that it can be hard to stay safe while studying them up close. This gets particularly true if there are interactions between the lava and snow or ice, which can cause flooding, explosions from rapid vaporization, and other unpleasant things.
However, by using a tilt furnace, small batches of rocks (basalt) can be remelted and poured under controlled circumstances. This allows studying what happens when lava flows over an ice sheet (video above), or even what happens underwater when lava comes up from the seafloor (video below), where structures called pillows are formed. Small-scale experiments like these can help scientists understand what determines which shapes the lava will take on under which conditions (slope, effusion rate, temperature).
Developed by NOAA, Science on a Sphere is a 1.7-meter diameter globe, surrounded by four projectors, which can display animated digital maps of the globe. Because the display is actually spherical, the maps do not have edges or strongly distorted projections, which can make looking at rectangular maps confusing.* On this display, it makes perfect sense why a flight from Los Angeles to Beijing would go near or over the Aleutian Islands of Alaska.
Many, many maps are available, covering a variety of topics including biology, geology, meteorology, planetary science, oceanography, and geography. There are maps of temperature changes going forward a hundred years, generated for each of the scenarios in the IPCC’s latest report. There are near-real-time maps of clouds seen (in infrared) by NOAA’s GOES and POES weather satellites. A near-real-time feed of earthquakes, coded by size and depth, is provided by the USGS. Following a tsunami, NOAA provides computer model output showing the wave heights as the waves travel across the ocean.
You can see the paths of commercial airplanes, the Earth at night, agricultural regions and their productivity, and the locations of volcanoes worldwide. Even the Moon, other planets (particularly Mars), and the Sun have their own visualizations.
Through the marvels of modern technology, these datasets can be overlain on top of each other, paused, backtracked, and even marked up like a sportscaster.
I spent many hours with the SOS at the Lawrence Hall of Science while I was living in Berkeley. Not only did I have fun talking with visitors about science, but I brought my favorite dataset to Science on a Sphere: near-real-time true-color imagery from the MODIS instrument aboard NASA’sAqua satellite.
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.