The University of the West Indies Seismic Research Centre

Mt. Liamuiga
Mt. Liamuiga rises to a height of 1155 m (3792 ft) and has a summit crater ~900 m wide and 244 m deep. The summit of Mt. Liamuiga exposes remnant lava flows and/or domes but the most common deposits identified on the lower flanks of Mt. Liamuiga are pyroclastic deposits. Cliff exposures along the coastline reveal 5-30 m thick successions of pyroclastic deposits (fall, flow and surge deposits), debris avalanche deposits and lahar deposits. Lava domes are prominent on the flanks of the volcano at Brimstone Hill, Sandy Point Hill and Farm Flat. There are also apparently two small craters located on Bourke’s Estate (Baker, 1965) although these could not be located during this study and their origin is unknown. Age dates on deposits interpreted to have been erupted from Mt. Liamuiga range from 1620 to > 41,000 yrs BP . These are the youngest known deposits on the island. The lava domes on the flanks of the volcano have not yet been dated and it is not known what the relative ages of these features are with respect to the dated pyroclastic deposits from Mt. Liamuiga.

Mt. Liamuiga principally formed by effusive lava-dome forming eruptions. Periodically the lava dome collapsed producing pyroclastic flows, surges and airfall. During and after periods of heavy rainfall it is likely that lahars or mudflows were also common. A final phase of explosive magmatic activity is interpreted to have formed the steep-walled, deep crater that is present at the summit of Mt. Liamuiga and to have produced the thick succession of airfall deposits that blanket the NW part of the island.

Fumaroles are present within the crater of Mt. Liamuiga as well asand on the flanks of the volcano along the SW base of Brimstone Hill and along the coast below Brimstone Hill. Volcanic earthquakes have also been associated with Mt. Liamuiga and are discussed in more detail below (see Volcanic Earthquakes).

Historic Eruptions
There are two unsubstantiated reports of historic eruptions of Mt. Liamuiga in 1692 and 1843. The first report was by a Franciscan friar (Sloane 1694) who describes the island as being troubled by earthquakes and mentions an eruption “of a Great Mountain of Combustable Matter”. The second report comes from Capadose (1845) who describes a white spiral cloud of smoke and bubbling sulphurous springs from the crater of Mt. Liamuiga. There are no other historical reports to support the occurrence of either eruption and both of these alleged eruptions occurred immediately after major earthquakes. It is possible that the effects of the earthquakes were confused with genuine eruptions or that the earthquakes could have triggered minor eruptions.

Baker (1985) references S. Skerrit (pers. comm.) as describing a Carib legend about Brimstone Hill suggesting that the hill grew out of the lower slopes of Mt. Liamuiga. This suggests that the pre-Columbian Indians possibly witnessed the growth of Brimstone Hill.

Future Eruptions
Present and past studies indicate that the northern part of St. Kitts near to Mt. Liamuiga is the most likely location for future eruptions. The most likely style of eruption is an effusive lava dome-forming eruption. There is also evidence of past occurrences of explosive magmatic eruptions resulting in pyroclastic , fall deposits; however, in the past dome growth and collapse have been the dominant processes. Future effusive eruptions may occur either on the flanks of Mt. Liamuiga (e.g. as at Brimstone Hill) or within the crater itself.

Glossary
1 Pyroclastic flows and surges. A pyroclastic flow is a hot (100-600 0C), fast-moving (>100km/hr) mixture of ash, rock fragments and gas. They usually travel down valleys and cause total destruction of the area over which they flow. Pyroclastic flows have been the main cause of destruction and loss of life in Montserrat since 1995. A pyroclastic surge is a dilute turbulent cloud of gases and rock debris that moves above the ground surface at great speeds. These form in a similar way to pyroclastic flows, but their effects are more widespread. Pyroclastic surges can be either hot or cold.

2 Effusive eruption. Effusive eruptions occur when molten rock (lava) reaches the Earth's surface and erupts passively. The products of these eruptions are lava flows and lava domes. They generally occur when the gas content of the magma is low.