Nightingale Island

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  • 37.42°S
  • 12.48°W

  • 365 m
    1197 ft

  • 386011
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28 July-3 August 2004

According to a news report, a swarm of earthquakes occurred beneath Tristan da Cunha during the nights of 28 and 29 July. A scientist monitoring seismic activity from the Preparatory Commission for the Comprehensive Nuclear Test-Ban Treaty Organization, Vienna International Centre indicated that the main swarm lasted ~8 hours and occurred ~30 km below the volcano. After the swarm, there were a few individual earthquakes and then activity tapered off.

Source: Tristan Times

Index of Weekly Reports


2004: July

Weekly Reports


28 July-3 August 2004

According to a news report, a swarm of earthquakes occurred beneath Tristan da Cunha during the nights of 28 and 29 July. A scientist monitoring seismic activity from the Preparatory Commission for the Comprehensive Nuclear Test-Ban Treaty Organization, Vienna International Centre indicated that the main swarm lasted ~8 hours and occurred ~30 km below the volcano. After the swarm, there were a few individual earthquakes and then activity tapered off.

Source: Tristan Times


Index of Monthly Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

08/2004 (BGVN 29:08) Earthquake swarm on 29-30 July followed by floating pumice


Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

08/2004 (BGVN 29:08) Earthquake swarm on 29-30 July followed by floating pumice

[This event was originally assigned to Tristan da Cunha, but later work located the earthquake swarm on the SE submarine flank of Nightingale Island, about 40 km S.]

The Comprehensive Nuclear Test Ban Treaty Organisation (CTBTO) in Vienna operates a recently installed (July 2002) satellite-linked real-time hydroacoustic station on the island of Tristan da Cunha, with two elements (figure 1). These are designed to record T phases and use three-component short-period seismometers sampled at 100 samples per second. Roderick Stewart, a scientist with the CTBTO, reported that seismic activity, including several felt events, occurred in the vicinity of Tristan da Cunha in July and August 2004. This is the first time that seismicity near this volcano has been instrumentally recorded.

Figure 1. Map of the island of Tristan da Cunha showing the locations of the two CTBTO hydroacoustic stations. Station locations courtesy of R. Stewart, CTBTO.

An intense swarm of seismic activity was recorded, and felt, on the night of 29-30 July. The activity lasted approximately six hours and peaked around 2100-2200 UTC on 29 July. There were a number of large earthquakes in the swarm; the largest, at approximately 2220 UTC on 29 July, had a body-wave magnitude of 4.2. The epicenter was in the vicinity of the island, but location uncertainties make it impossible to say whether the source was onshore or offshore. Seismic activity continued to be recorded, and occasionally felt, throughout August 2004, but was declining slowly (figure 2). No long-period earthquakes or tremor signals were positively identified although, according to Stewart, the temporal pattern of the swarm appeared to be volcanic. A pseudo-RSAM plot of the data from one of the stations showed that the activity grew gradually to a peak over a period of two or three hours and that the larger events occurred after this peak.

Figure 2. Hourly count of earthquakes at Tristan da Cunha from 27 July to 31 August 2004. Events were counted manually on constant gain plots. The counts of earthquakes during the initial swarm were more than 100 per hour. Courtesy of R. Stewart, CTBTO.

Stewart described the earthquakes as follows. "All the earthquake signals were impulsive with well-developed P and S phases, typical of volcano-tectonic activity. With only two stations, it is not possible to determine individual hypocentres with any confidence and the locations of the earthquakes can only be inferred from general observations made on the data. First-motion analysis of the P waves was made difficult because the arrivals were very small on the horizontal components. However, it was possible to determine that the P wave was always arriving from the SE at both stations and that the angle of incidence of the arriving P wave was very steep, within 10 degrees of vertical. S-P times were between 4 and 5 seconds at both stations, with H09N1 typically a fraction of a second longer than H09W1. Depending on the velocities assumed, these S-P times indicate that the earthquakes were between 20 and 30 km from the stations. The simplest interpretation of both the above observations is that the earthquakes occurred at depth directly below the volcano. However, an offshore location to the SE cannot be ruled out. What is certain is that these events occurred close to the volcano."

Reports from the island of rocks floating in the water in the days following the seismic activity, along with an initial offshore estimate of the location of the largest earthquake (which had large uncertainties), led to speculation of an underwater eruption. One newspaper account from the Tristan Times on 6 August described "angular and not round" rocks seen by fishermen floating "all around the Island." In a 14 September BBC World Service interview, Island Administrator Mike Hentley stated that fishermen found "huge lumps of [pumice], up to 10 or 12 kg floating on the surface to the south/west of the Island." He further described the pumice as "a very crumbly, light grey stone." Samples of this pumice collected by James Glass (figure 3) are being sent to the Global Volcanism Program.

Figure 3. Photographs of pumice collected near Tristan da Cunha, August 2004. No scale or size description was provided with the photos, but the top photo of the single sample appears to have been taken on a window ledge and the bottom photo of multiple samples on a bench `seat cushion. Courtesy of James Glass, Tristan Times.

The Tristan Times also reported on 30 September that volcanologist Victoria Hards from the British Geological Survey (BGS) arrived on the island on 10 September to assess the potential threat of the recent seismic activity. She reportedly determined that the 29-30 July event was caused by rising magma 25 km SE of the island. She also noted that there was no sign of activity at the 1961 eruption site, and no eruption was imminent so there was no threat to the settlement. The BGS planned to monitor the seismic data over the next four months to assess any longer-term implications.

Information Contacts: David Booth, British Geological Survey, Murchison House, Edinburgh EH9 3LA, UK (Email: dcb@bgs.ac.uk); Roderick Stewart, Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organisation (CTBTO), Vienna International Centre, PO Box 1200, A-1400 Vienna, Austria (Email: roderick.stewart@ctbto.org); Juanita Brock and James Glass, Tristan Times (URL: http://www.tristantimes.com); BBC World Service (URL: http://www.bbc.co.uk/worldservice/).

Nightingale Island and the adjacent smaller Middle (or Alex) and Stoltenhoff Islands and associated small islets are the southernmost of the Tristan da Cunha island group. The heavily eroded Nightingale Island consists of early and late stage ash and agglomerate units with intervening massive trachytic intrusions and lava flows. Volcanic rocks were K-Ar dated at between 0.4 and 0.15 million years, and a radiocarbon date of about 39,000 yrs BP was obtained from an ash layer overlain by a lava flow. An earthquake swarm lasting 6 hours beginning on July 29, 2004 was followed by observation of large blocks of floating phonolitic pumice that washed up on Tristan da Cunha. The event was considered to have originated from an eruption associated with an earthquake swarm 37-53 km SSE of Tristan da Cunha on the submarine SE flank of Nightingale Island.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2004 Jul 29 2004 Jul 30 Confirmed 0 Historical Observations Submarine SE flank

The Global Volcanism Program has no synonyms or subfeatures listed for Nightingale Island.

The Global Volcanism Program has no photographs available for Nightingale Island.

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Baker P E, Gass I G, Harris P G, LeMaitre R W, 1964. Vulcanological report on the Royal Society expedition to Tristan de Cunha. Phil Trans Roy Soc London, 256: 439-578.

Maund J G, Rex D C, le Roex A P, Reid D L, 1988. Volcanism on Gough Island: a revised stratigraphy. Geol Mag, 125: 175-181.

Reagan M K, Turner S, Legg M, Sims K W W, Hards V L, 2008. 238U- and 232Th-decay series constraints on the timescales of crystal fractionation to produce the phonolite erupted in 2004 near Tristan da Cunha, South Atlantic Ocean. Geochim Cosmochim Acta, 72: 4367-4378.

Volcano Types

Stratovolcano

Tectonic Setting

Rift zone
Oceanic crust (< 15 km)

Rock Types

Major
Trachyte / Trachyandesite
Trachyandesite / Basaltic trachy-andesite
Trachybasalt / Tephrite Basanite
Phonolite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
0
0
27
258

Affiliated Databases

Large Eruptions of Nightingale Island Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.