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anic features including lava tube caves and cinder cones are present on the island 93 the mcdonald islands are a group of smaller volcanic islands located about 43 kilometres 27 mi to the west of heard island 83 the group includes three islands mcdonald island flat island and meyer rock 94 after a period of dormancy of around 75 000 years volcanic activity resumed on the islands during the 20th century with significant eruptions in 1992 and 1997 95 94 during the 1990s this volcanic activity caused the islands to grow and rise in elevation by nearly 100 metres 330 ft with the main island more than doubling in size and losing all of its vegetation 83 87 91 between 1994 and 2004 mcdonald island grew from about 1 square kilometre 0 39 sq mi to 2 5 square kilometres 0 97 sq mi and became joined to the nearby flat island by an isthmus 96 97 the eruptions also created a new volcanic cone several lava domes and pumice rafts 94 the island is surrounded by cliffs with heights of up to 230 metres 750 ft and has no permanent ice cover 10 96 98 formation and geology edit exposed section of drygalski formation rock on heard island heard island and the mcdonald islands lie on the kerguelen plateau a large igneous province rising up to 3 kilometres 1 9 mi above the surrounding ocean floor on the antarctic plate that began forming about 130 million years ago 99 100 volcanic activity caused by the kerguelen hotspot has created various islands rising above the ocean surface over time including heard island and the mcdonald islands 101 100 102 a 2016 study estimated that heard island began to develop about 22 million years ago during the early miocene period 103 the volcanic activity that formed big ben is believed to have occurred over the last 1 million years while mawson peak mount dixon and the lava cones on the island formed as recently as the last 10 000 years 104 105 106 the mcdonald islands are also volcanic in origin and are believed to have formed within roughly the last 100 000 years 107 rocks from heard island and the mcdonald islands form two distinct lava series the newer lavas on heard island are primarily basaltic while the lavas on the mcdonald islands are phonolitic the heard island lava series includes basalts trachybasalts and basanites while the mcdonald islands lava series is characterised by compounds of phonotephrite tephriphonolite and phonolite 108 heard island s basement is made up of white and pink limestone likely deposited about 45 50 million years ago during the paleogene period which remains visible on parts of the laurens peninsula 87 89 on top of the island s limestone basement sits the drygalski formation a layer of volcanic rock and sediment about 300 350 metres 980 1150 ft in thickness that formed around 9 million years ago 87 104 109 the drygalski formation forms a plateau with exposed layers of rock along the island s northern coast 105 volcanic activity on the island over the last million years has added another layer to the stratigraphy and created big ben and mount dixon which lie on top of the drygalski formation s flat eroded base 87 104 110 heard island includes two distinct lava series the lavas of big ben are primarily composed of alkali basalts trachybasalts and basanites while the lavas on the laurens peninsula feature a distinct isotopic signature and more basanitic and trachytic compounds 94 according to one study the distinct isotopic compositions of the lavas on heard island indicate that the mantle beneath the island contains traces of continental crust that were incorporated into the mantle sometime before the separation of the landmass gondwana 111 big ben edit main article big ben heard island big ben stratovolcano on heard island big ben is a volcanic massif that forms the majority of heard island s landmass 100 112 it has a plateau at a height of about 2285 metres 7497 ft which is topped by mawson peak an active volcanic cone 112 113 the plateau is believed to be the result of a sector collapse that occurred some time in roughly the last 40 000 years 87 114 the volcano has a diameter of about 18 20 kilometres 11 12 mi and a height of 2745 metres 9006 ft 5 a 2021 study estimated that the age of two samples of lava taken from the volcano was around 11 100 and 23 900 years the volcano has a relatively low average discharge rate of about 200 000 cubic metres of magma per year and forms part of one of the world s oldest plume systems 39 100 only three parties have successfully reached the summit of big ben the first ascent was made by the southern indian ocean expedition in 1965 the second by the anaconda expedition in 1983 and the third by the australian army alpine association in 1999 2000 61 115 the volcano frequently emits smoke and vapour and occasionally releases lava typically down its south western slopes 116 flows of lava with lengths of 250 2000 metres 820 6560 ft have occurred roughly once per year since 2008 117 the volcanic activity on big ben is primarily effusive characterised by flowing lava rather than explosive 100 its peak has featured a crater of varying size and location between 2000 and 2015 mawson peak was topped by an open crater containing a lava lake with a diameter of 45 200 metres 148 656 ft while more recent observations have suggested that the crater may have been replaced by a fissure 117 118 119 glaciers edit see also heard island glaciers and list of glaciers of heard island and mcdonald islands coast of heard island heard island has been covered by glaciers since as early as the miocene epoch and experienced its most recent glacial maximum about 18 000 years ago 120 heard island has 12 major glaciers radiating outwards from the summit of big ben which are sometimes divided by barriers of volcanic rock 5 121 a 2025 glacier mapping study identified around 30 glaciers 122 as of 1999 the longest of these glaciers had a length of 7 kilometres 4 3 mi parts of the island s coast are made up of ice cliffs with heights of up to 30 metres 98 ft 5 112 123 other glaciers on heard island primarily those that flatten into a shallow incline terminate in moraines these are primarily composed of sediment and debris with relatively little till content 124 most of the glaciers flowing from the summit of big ben have a narrow top and a slope of more than 30 near its peak reducing to around 5 as they widen on its lower slopes 125 126 due to big ben s steep slopes and the high levels of snowfall on heard island its glaciers are fast flowing and have a short residence time of about 100 years the glaciers shallowness and fast movement mean that they are particularly vulnerable to changes in climate 126 127 128 many glaciers on heard island have retreated by more than 1 kilometre 0 6 mi since 1949 leaving substantial lagoons and lakes at their bases 129 130 one of the largest glaciers on heard island stephenson glacier ended in 15 metre 49 ft ice cliffs in 1954 but by 1963 terminated 100 metres 330 ft from the ocean behind a land barrier and a lagoon now known as the stephenson lagoon 131 132 its rate of recession increased from an average of 18 metres 59 ft per year between 1947 and 1987 to a rate of 100 metres 330 ft per year between 1987 and 2000 133 another glacier brown glacier lost 38 percent of its volume and 29 percent of its area while retreating by 1 17 kilometres 0 73 mi between around 1950 and 2004 134 135 a 2025 study estimated that the annual rate of glacier loss had increased from 0 25 percent between 1947 and 1988 to 0 43 percent between 1988 and 2019 total glacier area declined from an estimated 289 4 square kilometres 111 7 sq mi in 1947 to 225 7 square kilometres 87 1 sq mi in 2019 with smaller glaciers in low lying areas near laurens peninsula the most affected 136 climate edit kármán vortex street over heard island the territory of heard island and mcdonald islands has an antarctic climate 137 it experiences strong westerly winds high precipitation and heavy cloud cover 83 98 138 average daily temperatures at atlas cove on heard island are between 0 8 c 30 6 f and 0 3 c 32 5 f in winter and between 3 7 c 38 7 f and 5 2 c 41 4 f in summer monthly wind speeds range from 26 kilometres per hour 16 mph to 33 5 kilometres per hour 20 8 mph on average with maximum daily gusts of up to 180 kilometres per hour 110 mph 98 the islands experience high snowfall and rainfall with an average annual precipitation of 1 3 1 9 metres 4 3 6 2 ft water equivalent 5 between 1948 and 1950 there was an average of just 1 7 hours per day of sunshine ranging from 0 8 hours per day in june to 2 4 hours per day in november rain or snow was recorded on an average of 300 days each year 105 112 the territory has consistently high humidity with relative humidity of about 85 percent 139 while meteorological data for the island is incomplete the average annual temperature on heard island is estimated to have increased by about 0 8 c between the periods 1948 1954 and 1997 2005 98 140 climate change is believed to be the main driver of glacier retreat on the island although volcanic activity has also been suggested as a potential contributing factor 141 142 143 climate change has also led to significant changes in the island s vegetation due to the creation of new ice free land lagoons and lakes 144 biodiversity edit king penguin colony on heard island due to the territory s remoteness scientific surveys of the heard and mcdonald islands are infrequent and there is limited recent data on the islands biodiversity 43 about 300 species are known to be present on heard island although it is likely that there are others that have not yet been recorded 145 heard island and the mcdonald islands are the only sub antarctic islands that are not home to any species known to have been directly introduced by humans 39 96 b various non native animal species have been brought onto heard island by humans in the past including dogs sheep and at least one rat but none have established a presence on the island 24 146 the islands have relatively low species diversity 43 95 a 2021 study projected that climate change would cause the populations of penguins flying birds and seals on the island to decline the population of toothfish in the surrounding waters was projected to fall by 20 60 percent while the population of mackerel icefish was projected to fall by 20 percent 147 flora edit azorella selago and pringlea antiscorbutica on heard island lichens on a rock on heard island the majority of the plant species on heard island are non flowering plants including bryophytes a division of plants that includes liverworts and mosses and lichens at least 62 species of bryophyte and 90 species of lichen have been recorded on the island there are just 12 species of vascular plants on heard island 5 of which have also been recorded on mcdonald island 44 148 about 20 square kilometres 7 7 sq mi or 5 percent of the island is covered by vegetation mostly in low lying coastal areas with elevations of less than 300 metres 980 ft 44 149 150 the antarctic ecologists dana bergstrom and patricia selkirk have compared heard island to an archipelago of distinct vegetation communities separated by ice 151 researchers studying plant microfossils on heard island have suggested that several species of plant including ferns a podocarp and a small herb were present on the island between the late eocene and early pliocene periods volcanic activity over the last million years disrupted many of these early plant communities and during colder periods in the pleistocene epoch many plant species disappeared from heard island 152 today the level of vegetation on the island is increasing due to glacier retreat which is making new land available for plant colonisation 153 154 vegetation remains absent from some areas due to high levels of nitrogen ammonia and other compounds deposited by the island s large colonies of seabirds 155 the most prevalent vegetation on the island is azorella selago a species of cushion plant 44 156 the majority of the other vascular plants on the island are small herbs and grasses with the exception of pringlea antiscorbutica known as kerguelen cabbage the island does not contain any trees or shrubs 10 144 pringlea antiscorbutica is present largely on gravel and sandy areas with high moisture and drainage particularly on moraines 157 the island s grasses include poa cookii a small tussock grass as well as tufts of poa kerguelensis 158 the island s wetlands are characterised by the presence of the herb callitriche antarctica 159 a non native grass poa annua has significantly expanded its presence on the island including on formerly glaciated land this expansion has led to fears of potential displacement of native plants 43 160 the moss species present on heard island are relatively uniformly distributed across the island 161 the most widespread mosses on heard island are species of dicranoweisia while other common mosses include polytrichastrum alpinum racomitrium crispulum ditrichum immersum and pedinophyllopsis abdita 162 163 164 salt tolerant plants particularly the moss muelleriella crassifolia are prevalent in coastal areas exposed to sea spray and many of the rocks on heard island are covered in lichens 165 166 as of 2008 90 lichen species had been identified on heard island nine of which had not previously been recorded elsewhere 167 148 fauna edit birds edit see also list of birds of heard and mcdonald islands the heard island cormorant is unique to heard island fifteen flying seabird species are known to breed on heard island and at least fifteen others have been recorded visiting the island 44 168 the species that breed on heard island include three species of albatross and seven species of petrel 46 the territory is visited by four endangered seabird species the northern royal albatross the amsterdam albatross the tristan albatross and the grey headed albatross and eight vulnerable species the southern royal albatross the sooty albatross the indian yellow nosed albatross the campbell albatross the white capped albatross the northern giant petrel the blue petrel and the soft plumaged petrel 46 the most abundant flying birds are petrels while several species of albatross including the wandering albatross have a presence on the island 168 there are two types of seabird found only on the island the heard island cormorant and the heard island sheathbill a subspecies of black faced sheathbill 44 the population of heard island cormorants has been estimated at around 1000 pairs 169 four species of penguin breed on heard island the macaroni penguin gentoo penguin king penguin and eastern rockhopper penguin 44 168 four other penguin species have been recorded visiting the islands 170 there have been reports of possible emperor penguin sightings on heard island although none have been confirmed 171 the population of king penguins has risen exponentially from a small number of breeding pairs in 1947 to more than 100...
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