The first recorded volcanic eruption in Antarctica occurred on Bridgeman Island (South Shetland Islands) in early 1821, < 2 years after Antarctica was discovered. However, the observations were disputed owing to a lack of physical evidence. A consensus arose that they probably referred to Penguin Island, a young volcano with a well-formed volcanic cone situated just 60 km to the west. However, a recent re-examination of the historical reports demonstrated that the event was undoubtedly located at Bridgeman Island. Our new study demonstrates that the eruption was explosive and lasted throughout 1821. The vent was situated in the sea ~500 m to the west of Bridgeman Island and the eruption was hydrovolcanic (Surtseyan). The new volcano constructed a tuff ring composed of unconsolidated lapilli and ash, which rapidly coalesced with nearby Bridgeman Island, similar to how the Capelinhos volcano joined with neighbouring Faial (Azores) in 1957–1958. The tuff ring had a very low profile and was rapidly removed by marine erosion. However, fumarolic activity persisted for a few decades. Because the eruption is only 200 years old, the underlying volcanic construct (Bridgeman Rise) should be regarded as dormant rather than extinct.

The youngest pre-caldera volcanism of Deception Island is represented by a thick sequence of subaerial pyroclastic deposits which has been grouped as the Yellow Tuff Formation. Most of these deposits were related to the explosive activity of a central vent which was destroyed during the formation of the caldera. Two members can be distinguished in this formation. The lower member is mainly composed of 1 to 12 m thick massive pyroclastic flow deposits with interbedded air-fall and surge deposits. The upper member is in stratigraphical continuity with the lower member and consists of base surge deposits with minor air-fall and thin pyroclastic flow deposits. The pre-caldera deposits have undergone a palagonitic alteration which produced crystallization of smectites, Fe-oxides, zeolites and calcite.

Contact relations and petrography of the volcanic breccia known as the Stac Fada Member, near Stoer, show that it is not a simple sediment-gravity flow, but was generated lower in the sedimentary succession by phreatomagmatic activity and rose to the surface as buoyant peperitic slurry. A previously undescribed part of the member, 9 m below the intrusive base of the main ‘flow’, has an intrusive top. Vesicle trains within the breccia matrix suggest that the slurry was boiling at a temperature of at least 160°C.