The Heard and McDonald Islands are the most remote territory of Australia. They are uninhabited, sub-Antarctic islands in the Southern Indian Ocean and are closer to Antarctica than they are to Australia. The closest islands to these two are the Kerguelen Islands 450 km to the NE. The three islands have been classified as part of an extended wildlife preserve to minimize human visitation.
Heard Island is by far the largest at 368 km2. It is generally covered with glaciers. The island is built by a massive volcano called Big Ben. Its highest point is 2,790 m Mawson Peak, the highest point in Australia. The volcano is active, with the highest point growing by 45 m over the last 19 years. The most recent eruption was Feb 2016. There is a smaller island to the NW connected to the main island by a narrow isthmus.
The McDonald Islands are much smaller, totaling only 2.5 km2 in surface area topping out at less than 190 m. The volcano on McDonald Island was dormant for 75,000 years, became active in 1992, erupting several times, most recently in 2005.
The islands have no ports and visitors must anchor offshore. They were first observed in 1854. They are 4,100 km SW from Perth in Western Australia, 4,200 SE from South Africa, and 1,630 km north of Antarctica, a truly remote part of the world.
Climate is Antarctic Maritime, severe with low seasonal temperatures, persistent low cloud cover, frequent precipitation and strong winds. Snowfall is sufficient to maintain a glacial cap on Big Ben with at least 14 active glaciers. These glaciers have carved large valleys into the flans of Big Ben. Due to its remoteness, extensive past meteorological records are at best incomplete.
Plant life on the islands is constrained by the cold, salt spray, ice cap and volcanic activity. Low growing plants, arctic lichens, mosses and liverworts can be found. Some of the low plants are thought to be leftovers from periods of time before the climate turned colder. Heard Island is the largest island with no confirmed human-introduced plants or predators.
Seals were hunted at Heard 1855 – 1910. Seal populations were wiped out to the extent sealing was no longer an economic enterprise. Since sealing ended in the 1920s, seal populations have gradually increased and are currently protected.
The islands provide an excellent rookery for at least 19 breeding species of birds. At least another 28 species have been observed. There are no known predators on the islands for the birds.
There was a 2016 Cordell Expedition to Heard Island. Its web site at the previous link has a wealth of information and most importantly photos of their visit. The photography is breathtaking. A previous Cordell Expedition took place in 1997.
Heard Island is probably younger than 1 Ma. It sits on a basement of limestone with outcrops mainly on the Laurens peninsula and sporadically beneath Big Ben. The island history probably began 22 Ma with an uplift of limestone and volcanic sills. Subaerial and wave action leveled the early island, creating a depression that pillow lavas, hyaloclastic rocks and shallow water siltstones were deposited.
Two recent volcanic systems, Big Ben and Mount Dixon, began activity above the surface. Feeder dikes and early lava flows in both systems date back 400 – 200,000 years. Trachyite and trachyandesites erupted 100 – 20,000 years ago. Well preserved parasitic cones at low elevations date 15 – 10,000 years ago. Finally, Big Ben via Mawson Peak currently erupts lava flows.
Big Ben is a is a large composite basalt to trachyte stratovolcano around 25 km in diameter that dominates the island. There is a smaller satellite volcano, Mount Dixon that makes up the Laurens Peninsula to the NW of the main island. It tops out at Anzac Peak at 715 m. Both cones are young, but Big Ben is the only one observed to erupt.
The main cone is topped with a 5 – 6 km diameter caldera at 2,200 – 2,400 m breached to the SW side by either a flank collapse or lateral blast. This Recent activity built the new cone, Mawson Peak within the breached portion of the summit. It is snow and ice covered on all sides. Historic activity appears to all come from Mawson.
Mount Dixon is a smaller, recent volcano. Activity building it created a peninsula 9 km long and up to 5 km wide to the NW of the main island. It is a glacier-covered rounded cone. More than 20 young basaltic lava flows have been identified on its flanks. Two of these appear to be recently erupted, perhaps in the last couple hundred years. The flows appear to come from vents on its upper flanks except one from a fissure marked by a scoria ridge around a kilometer long on the base of the southern flank. There is a 50 m crater at the head of one west flank flow. Trachyte lavas are below newer basalt flows on the W and N flanks.
There are 11 small parasitic satellite scoria cones located on the northern flanks. Some are at or near the edges of vertical sea cliffs, meaning erosion may have taken other cones. These are typically 100 m high, well formed, with deep central craters. There is generally lava spatter around the upper portions of the cones. Lavas from these cones are typically low volume basaltic pahoehoes and appear to be only a few thousand years old.
There is an older parasitic cone on the Azorella Peninsula (to the NE of the peninsula connecting Mount Dixon to the greater Heard Island) that appears to be the remnant of an older and much larger tuff cone. The lava flow from this cone contains lava tunnels.
Another young trachytic ashfall pumice deposit 1 – 1.5 m thick is found at the eastern end of the island. The older half meter of the deposit is distinctly darker than the upper portion. It is a primary deposit and its source is currently unknown. This sort of deposit is interesting as most of what is erupted from Heard Island are lavas with not a substantial amount of ashfall or pumice.
Video of Big Ben in eruption taken Jan. 2016 from CSIRO research vessel Investigator.
Heard Island Eruptions
Heard Island is the only currently active volcano in Australia. Volcanic activity has been observed here since 1881. There was an eruption in 1993. Satellite imagery detected eruptions in 2000. Plumes from a 2001 eruption were observed from a visiting boat. Several hotspots showed up in satellite imagery 2003 – 2008 and 2012.
Several subglacial eruptions have been reported, but observations are infrequent and probably missed eruptions. At least 13 eruptions have been observed since 1881. They were VEI 2 or smaller and all from either Mawson Peak or the upper south flank of the volcano.
The following is a combined synopsis of Smithsonian GVP satellite observations of Heard:
The MODIS instrument detected 10 thermal alerts at or near the summit of Big Ben March – June 2006.Satellite imagery showed thermal imagery in Sept and Oct 2012. Visual wavelength imagery in October showed a possible dark area in the Mawson Peak crater and a hot surface in the crater. NASA Earth Observatory posted an April 2013 image of Heard showing the crater had filled and a lava flow traveled down the SW flank. A NOAA satellite detected thermal anomalies on the E flank in Nov 2014. Other thermal anomalies were observed from July – Sept 2014. These were thought to be lava flows down the flanks or a persisting lava lake in the crater. There was a plume visible from Heard in a satellite image Oct 2015.
The most recent eruption was reported by visiting scientists in Jan. 2016. They observed a plume and lava flows down the NW flanks. The video of this eruption can be found below:
Thermal hotspots were observed Oct 2018 – March 2019 at the summit and on its upper flanks. Satellite imagery was difficult due to persistent cloud cover. Normal location was on the summit vents. An October anomaly was observed 300 m down the E flank. A Jan anomaly was observed 200 m down the NW flank. This one was 300 m long. The MIROVA system detected 3 hot spots in Oct – Nov.
The GVP also lists 10 Bulletin reports 1985 – 2004. Most of these are lava flows, steam plumes, glows, fumarolic activity, brown fumes, even a crater lake in 2004.
McDonald Islands are three small islands, McDonald Island, Flat Island and Meyer Rock. They are less than 100,000 years old. Activity here combines lava flows with explosive ashfall.
McDonald Islands are located 75 km W of Heard Islands. The largest island, McDonald is constructed of a layered phonolitic tuff plateau cut by dikes and lava domes. There is a possible active submarine volcanic center thought to be nearby based on phonolitic pumice that washed up on Heard Island in 1992. This has not yet been confirmed.
No volcanic activity was observed on McDonald Island between its discovery in 1874 through 1997. A 2001 satellite image showed the main island doubled in size. This was confirmed visually from a visiting cruise ship in 2002 and high-resolution satellite imagery in March 2003. This imagery showed a new volcanic complex with lava domes, spine evolution, lava flows and numerous fumaroles. The new activity connected the main McDonald Island with neighboring Flat Island with a 1 km long spit. The high point on the island shifted the north end of the island group.
Volcanic activity between Jan. 1999 – Nov. 2000 significantly changed the shape of the island. This was first discovered in Nov. 2000 by a passing ship which observed vigorous venting of volatiles. Activity was dispersed at several points high on the flanks of the island with pulsing fumaroles putting emissions as high as 50 m. These emissions were mostly on the northern flanks of the island. These emissions were not as vigorous as those observed in Jan. 1999 and were sourced higher on the slopes of the island than those in 1999 and 1997, though actual location on the island was similar.
The eruption significantly changed the shape of the island. Steep coastal slopes were replaced by slopes of a more moderate angle. The skyline of the mountain changed from a relatively smooth, vegetated upper slopes to one that was more jagged bare rock. Satellite imagery comparing Nov. 2001 with aerial photography from 1980 showed McDonald Island which had been 1.13 km3 was now 2.45 km2, more than doubling in size and connecting McDonald and Flat Islands. Most new features appear to be volcanic.
A passing research ship in 2002 observed steaming slopes and what they described as “two types of lava dome.” The highest point of the island migrated from the southern to the northern end. Flat Island was now connected by what appeared to be a narrow isthmus of volcanic debris. Several meters of ash now blanket the northern half of the island.
The eruption may or may not had an impact on nesting or breeding wildlife. A species of penguin normally found in large numbers had those numbers fall considerably. A second species of penguin not normally found was now found in moderate numbers on the island. Such a change may or may not be related to the eruption, but it will take a full-scale scientific visit to find out for sure.
McDonald Island Eruptions
Modern activity at McDonald Island is assumed to have started Dec. 1996 and continued through early 1997. Initial reports from pilot, passing ships and a Jan. 1997 satellite image of a plume in the region all assumed the activity was from Mawson Peak on Heard Island. This changed in March 1997 when a research ship on its way to Heard Island passed within 8 km of McDonald Island and observed steam plumes emitted at high velocity from several point sources and a fissure system on the island’s northern face. They also observed a low diffuse white vapor plume extending SE from the islands northern summit. Steam vented from a rubble-covered slope that may have been a lava flow or pyroclastic deposit.
A second ship passing within 3 -5 km April 2, 1997 observed steam venting similar to that reported in March. They also reported “smoke” clouds rising from the summit and flanks of the northern and middle parts of the island, possible lava flows down gullies and a yellow-green deposit (sulfur?) close to the source of steam venting. The diffuse white plume from the northern summit observed in March was still active. This trip took photos.
Observers never went ashore during or after the eruption but did produce a sketch of what they described as new lavas.
The March 1997 research ship continued on to Heard Island, where they sampled recent lava flows. They found fresh pumice up to 20 cm in diameter on the beaches of the Laurens Peninsula that looked to have been deposited by wave motion.
There was no evidence of recent volcanic activity on Heard Island at this time nor was a plume observed from Big Ben by either research vessel. Note that volcanic activity from Big Ben is typically lava flows and not explosive. Whatever produced the chunks of pumice must have done so explosively.
Fumarole activity was observed on McDonald Island by a passing research ship in Jan. 1999. No volcanic activity was observed on Heard Island at the time. The steam was coming from multiple point sources. They also observed a rubbly flow / fall deposit in a valley extending north from the fumarole field to near the shoreline. Most of the activity were on the N and NE flanks of the island.
The island significantly changed shape between Jan. 1999 and Nov. 2000, almost doubling in size.
Satellite infrared data suggested a new eruption in June 2005 when two-night ASTER images showed activity centered on the NW shore of the island. A more recent ASTER image in July 2005 showed a larger IR anomaly and at least five saturated pixels in the short IR part of the spectrum, indicating a significantly hot target. This is thought to be effusive activity. There was an earlier alert in Nov. 2004.
A passing research vessel in late Jan. 2016 observed a plume rising from McDonald Island.
The Heard and McDonald Islands are part of the larger Kerguelen Plateau, one of the largest Large Igneous Provinces (LIPs) on the planet. The islands are in the relative middle of the LIP, one of the youngest portions of the Province. Writers in our former home had a couple posts on the overall Kerguelen Plateau, one in 2015 and one in 2012.
The full plateau is immense, over 2,000 km long, covering 2.2 million km2, with a total volume over 25 million km3. For the most part, it tops out at 1 – 2 km below the ocean surface, on an abyssal plain 3 – 4 km below the surface. It is also quite old, with earliest eruptions starting some 120 Ma in the southern end of the plateau. The northern end with the Kerguelen Islands is 40 Ma. The central and youngest portion with Heard and McDonald Islands has the only active volcanoes above the surface.
The plateau has coal and shallow-water sediments, including coal, indicating that large portions of it were above or just below the surface tens of millions of years ago before it subsided. There is a layer of limestones deposited over much of the plateau deposited 40 – 50 Ma. Drilling discovered charcoal in parts of the plateau. This means that parts of the plateau were more recently above the surface and forested. These parts are now 2 km below the surface of the Indian Ocean. Most of the subsidence took place some 20 Ma.
Early volcanic activity was driven by the fragmentation of Gondwana, and as it progressed, the LIP started forming. Africa / South America first split off Gondwana 150 – 130 Ma. India separated next and started quickly moving north. Oz finally separated from Antarctica last around 100 Ma. Kerguelen magmas started filling the gaps in the crust created by spreading centers starting after India and Oz separated from Antarctica.
The interplay and movement of various spreading centers over the last 100 Ma as India, Oz and Antarctica separated drove the growth of the Kerguelen. For instance, the SouthEast Indian Ridge cut the Kerguelen Plateau when it formed 43 Ma, moving the original northern end of the LIP north. That portion is now referred to as Broken Ridge. We saw this same sort of thing with the Ontong Java Plateau. Ridge movement in this portion of the Indian Ocean has been quite complex and has in turn opened the crust for massive eruptions of magmas. Some sources describe the Kerguelen as a microcontinent, though most of it is now below the surface of the ocean.
The problem with an interesting pair of volcanic systems like Heard and McDonald Islands is their remoteness. They are just a long, long way from anything. This makes any continuing observation, research and geology difficult at best. It looks like both islands are currently active. As such, they are more of a danger to local wildlife than visitors, though that would certainly change if an expedition to the islands takes place. These islands are a most interesting part of the world.