[edit]
A large Kelvin wake cloud formation, caused by lee waves from Île Amsterdam (lower left).
Geography[edit]
The island is a potentially active volcano. It has an area of 56.6 km2 (21.9 mi2), measuring about 10 km (6 mi) on its longest side, and reaches as high as 867 m (2,844 ft) at the Mont de la Dives. The high central area of the island, at an elevation of over 500 metres (1,600 ft), containing its peaks and caldera, is known as the Plateau des Tourbières (transl. Plateau of Bogs). The cliffs that characterise the western coastline of the island, rising to over 700 metres (2,300 ft), are known as the Falaises d'Entrecasteaux after the 18th-century French navigator Antoine Bruni d'Entrecasteaux.
There are no lakes nor rivers on the island; the only freshwater bodies are small ponds on the plateau. The low altitude areas are dry and fires have happened repeatedly.
Geology[edit]
Île Amsterdam vent, crater and caldera structures. Click on map to enlarge it where upon mouse over is enabled so selected structures can be identified. Zoom out accesses approximate surface projections of nearby submarine structures.
No historical eruptions are known, although the fresh morphology of the latest volcanism at Dumas Craters on the northeastern flank suggests it may have occurred as recently as the late 19th century. All the rocks are tholeiitic basalt and the oldest basalt sampled is no more than 720,000 years old.: 181 
There are two stratovolcanoes being Mont De La Dives which dominates and is younger and Le Mount du Fernand. Vents manifest as either cones or craters include Cratere Antonelli, Le Brulot, Le Chaudron, Le Cyclope, Crateres Dumas, Le Forneau, Cratere Inferieur, Grande Marmite, Cratere Hebert, Museau De Tanche, Cratere de l'Olympe, Cratere Superieur, Crateres Venus, and Cratere Vulcain (see map on this page).
The island is located on the mainly undersea Amsterdam–Saint Paul Plateau which is of volcanic hotspot origin.: 128  There is a magma chamber located at between 20–36 km (12–22 mi) depth below Amsterdam Island. The plateau which extends north west towards the Nieuw Amsterdam Fracture Zone (Amsterdam Fracture Zone) and south to beyond the island of St Paul with its presently known active area being delimited by the St. Paul Fracture Zone, is a 250 by 200 km (160 by 120 mi) feature of the sea floor near the Southeast Indian Ridge, which is an active spreading center between the Antarctic plate that the island lies on, and the Australian Plate.: 180  Helium isotopic compositional studies are consistent with its formation from the combined effects of accretion at the mid-ocean ridge ridge and mantle plume activity of a hot spot.: 180  This is either the Kerguelen hotspot or a potentially separate Amsterdam-Saint Paul hotspot but resolution of this issue is complicated by the recent volcanism on the island due to it being adjacent to the Southeast Indian Ridge.: 1177 : 128  Recent authors have favoured a separate Amsterdam and St. Paul hotspot. There has been evidence at Boomerang Seamount to the north east of the island that Kerguelen-type source mantle exists beneath the Amsterdam and St. Paul Plateau.: 257  Whichever hot spot is responsible is moving south as Île Amsterdam rocks are older than St. Paul rocks.: 181  The Amsterdam–St. Paul Plateau while formed in the last 10 million years, started this formation beneath the Australian Plate so the island is built on the components of two tectonic plates.
Climate[edit]
Île Amsterdam has a mild, oceanic climate, Cfb under the Köppen climate classification, with a mean annual temperature of 14 °C (57.2 °F), annual rainfall of 1,100 mm (43 in), persistent westerly winds and high levels of humidity. Under the Trewartha climate classification the island is well inside the maritime subtropical zone due to its very low diurnal temperature variation keeping means high.
Climate data for Amsterdam Island (Martin-de-Vivies, 1991–2020 normals, extremes 1950–present)
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
Record high °C (°F)
26.1(79.0)
26.2(79.2)
24.8(76.6)
23.4(74.1)
21.0(69.8)
20.3(68.5)
18.2(64.8)
17.7(63.9)
23.9(75.0)
19.2(66.6)
22.4(72.3)
24.8(76.6)
26.2(79.2)
Mean daily maximum °C (°F)
20.6(69.1)
20.9(69.6)
20.0(68.0)
18.1(64.6)
16.2(61.2)
14.6(58.3)
13.8(56.8)
13.6(56.5)
14.3(57.7)
15.0(59.0)
16.6(61.9)
19.0(66.2)
16.9(62.4)
Daily mean °C (°F)
17.6(63.7)
17.9(64.2)
17.2(63.0)
15.7(60.3)
13.8(56.8)
12.3(54.1)
11.5(52.7)
11.3(52.3)
11.9(53.4)
12.5(54.5)
14.0(57.2)
16.1(61.0)
14.3(57.7)
Mean daily minimum °C (°F)
14.5(58.1)
15.0(59.0)
14.5(58.1)
13.2(55.8)
11.5(52.7)
10.1(50.2)
9.2(48.6)
8.9(48.0)
9.5(49.1)
10.0(50.0)
11.3(52.3)
13.2(55.8)
11.7(53.1)
Record low °C (°F)
6.1(43.0)
4.5(40.1)
6.0(42.8)
4.3(39.7)
3.8(38.8)
3.0(37.4)
1.8(35.2)
1.9(35.4)
2.1(35.8)
3.1(37.6)
4.7(40.5)
1.7(35.1)
1.7(35.1)
Average precipitation mm (inches)
68.3(2.69)
62.7(2.47)
100.0(3.94)
93.3(3.67)
121.5(4.78)
114.8(4.52)
112.1(4.41)
87.8(3.46)
74.8(2.94)
75.7(2.98)
77.0(3.03)
70.0(2.76)
1,058(41.65)
Average precipitation days (≥ 1.0 mm)
9.3
9.1
11.1
12.4
16.8
17.9
18.3
16.9
14.7
13.8
11.7
10.1
161.9
Average dew point °C (°F)
13(55)
13(55)
13(55)
11(52)
10(50)
8(46)
8(46)
7(45)
6(43)
7(45)
9(48)
11(52)
10(49)
Mean monthly sunshine hours
177
145
134
110
107
99
104
121
123
141
150
170
1,581
Source 1: Météo France
Source 2: NOAA (sun 1961–1990), Meteo Climat (record highs and lows) Time and Date (dewpoints 2005–2015)
Flora and fauna[edit]
Further information: Amsterdam and Saint-Paul Islands temperate grasslands
Phylica arborea grove
Vegetation[edit]
The main plant living on the slopes below 250 metres (820 ft) of altitude is the tussock grass species Poa novarae. Up to 600 metres (2,000 ft), sedges such as Scirpus nodosus and Spartina arundinacea build up thick grasslands. Beyond that altitude moss, sphagnum and Acaena magellanica dominate the vegetation.
Phylica arborea (Thouars) trees occur on Amsterdam, which is the only place where they form a low forest, although the trees are also found on Tristan da Cunha and Gough Island. It is called the Great Forest (Grand Bois). Before human presence, it covered the lowlands of the island, until forest fires set by sealers cleared much of it in 1825.[citation needed] The Phylica of Île Amsterdam were previously assigned to Phylica nitida (Lam.), but phylogenetic studies showed they do not belong to the same species as the Phylica nitida from highlands of Réunion and Mauritius.: 818 
From 1696 to 1988, the botanical composition of the coastal areas is deeply impacted by wildfires, wood-cutting, and by the introduction of alien plants and animals, especially cattle. Sailors from HMS Raleigh, who visit the island on 27 May 1880, describe the vegetation as:
Rough ground, grass several feet high, myrtle 10–15 feet [3–5 m] high in sheltered ravines, sedge, ferns (principally polypodium) and cabbages, grown into bushes with stumps several inches thick in the garden [...].
In the beginning of the 1980s, the population of Phylica is limited to a forest of about 5 ha and a few fragments; in 1988, it occupies 10 ha. From 1988 on, however, restoration interventions erect fences and later cattle is removed, while over 7000 Phylica arborea are planted.
Birds[edit]
Terrain map of the island showing the research base.
The island is home to the endemic Amsterdam albatross, which breeds only on the Plateau des Tourbières. Other rare species are the brown skua, Antarctic tern and western rockhopper penguin. The Amsterdam duck is now extinct, as are the local breeding populations of several petrels. There was once possibly a species of rail inhabiting the island, as a specimen was taken in the 1790s (which has been lost), but this was either extinct by 1800 or was a straggler of an extant species. The common waxbill has been introduced. Both the Plateau des Tourbières and Falaises d'Entrecasteaux have been identified as Important Bird Areas by BirdLife International, the latter for its large breeding colony of Indian yellow-nosed albatrosses.
Mammals[edit]
There are no native land mammals. Subantarctic fur seals and southern elephant seals breed on the island. Introduced mammals include the house mouse, brown rat and feral cats.
A distinct breed of wild cattle, Amsterdam Island cattle, also inhabits the island from 1871 to 2010. They originate from the introduction of five animals by Heurtin during his brief attempt at settlement of the island in 1871 and increase to an estimated 2,000 by 1988. Following recognition that the cattle are damaging the island ecosystems, a fence is built restricting them to the northern part of the island in 1988. In 2007 it is decided to eradicate the population of cattle entirely, resulting in the slaughter of the cattle between 2008 and 2010. Subsequently, native plants gradually recolonize the lowlands, and the population of Amsterdam Island albatrosses recovers from 5 breeding pairs in 1983 to 51 in 2018.
From the 18th century on, rodents and feral cats introduced by humans are significant threats to native wildlife. Rats prey on invertebrates and on the eggs and chicks of seabirds, they are vectors of disease, such as outbreaks of fowl cholera among Indian yellow-nosed albatross chicks, and they damage saplings, while mice eat seeds.
An eradication campaign of these invasive species is started in 2020. Cats are removed between 2020 and 2022. Rodents are trapped from December 2021 on. Poisoned bait is spread in 2024.
With this campaign, the survival rate of Indian yellow-nosed albatross chicks in the end of March 2023 amounts to 52%, while it was 4% in 2019 and 2020. The population of Amsterdam Island albatrosses recovers further from 51 breeding pairs in 2018 to 80 in 2025.
