December Eruption at Kick 'em Jenny
by Jan Lindsay
Kick 'em Jenny submarine volcano is located at 12°18' N; 061°38' W, just west of the Sisters Rocks and Ile de Ronde, and about 9 kilometres north of Grenada. It should not be confused with nearby Diamond Rock, which is also called "Kick 'em Jenny".
After spending months upgrading the Kick 'em Jenny monitoring network, and convincing the Government of Grenada of the wisdom of adopting a "Yellow Alert" and its associated 1.5 km exclusion zone for vessels transiting the vicinity, the underwater volcano rewarded the efforts of the University of the West Indies' Seismic Research Unit on Tuesday December 4, 2001 with a small eruption!
An alert system consisting of four levels is used at Kick 'em Jenny (see the November 2001 issue of Compass, or visit www.uwiseismic.com for details). Prior to the December eruption, the volcano was at alert level "Yellow". At this alert level it is recommended that boats stay 1.5 km away from the summit of the volcano. On December 4th the alert level was officially increased to "Orange" and remained there for the duration of the eruption. At this alert level it is recommended that boats stay 5 km from the summit. On Saturday December 8th, the alert level was decreased back to "Yellow".
The first signs of the underwater volcano's recent unrest were actually observed in October 2001, with a slight increase in seismic activity recorded at seismic stations close to the volcano. Then on December 4th, scientists at the Seismic Research Unit in Trinidad observed a burst of seismic activity beginning at 6:00AM (local time) and increasing to a peak at about 11:00AM. Following a short lull, activity again increased, and culminated in bursts of so-called "T-phase" between 7:18PM and 10.31PM. These bursts of T-phase were interpreted as explosions associated with a submarine eruption. After this burst of activity things quieted down, and earthquake activity returned to background levels.
T-phase, also known as "T-wave" is an acoustic wave from an earthquake or underwater explosion (e.g. submarine volcanic eruptions). When an earthquake occurs in the earth's crust under the ocean or a submarine volcano erupts, in addition to the usual earthquake waves - i.e. "P" (primary) and "S" (secondary) waves - a third wave (T-wave) is generated by the acoustic energy in the ocean. The "T" stands for "tertiary", because these waves travel the slowest and so arrive after both the P and S waves at seismic stations.
The December 4th eruption appeared to have been completely submarine, with no observed or reported activity at the surface (although it did occur at night, so we can't say for sure that there were no surface manifestations). Despite the lack of subaerial activity, the presence of T-phase confirmed that Kick 'em Jenny had erupted. The largest earthquakes associated with the eruption were felt in northern Grenada.
I was stationed in Sauteurs (north Grenada) at the Kick 'em Jenny Observatory for four days while the alert level was "Orange", and I had a great view of the sea. The whole time I was there I noticed yachts passing very close to if not directly over Kick 'em Jenny. This is very worrying, and I would stress that yachties should really make an effort to stay well away (at least 1.5 km, now that the alert level is back to "Yellow", or 5 km from the summit should the alert level again be elevated to "Orange"). The most obvious hazards of Kick 'em Jenny are those directly resulting from an eruption, and include the local disturbance of water and the rapid ejection of hot rocks and ash into the water column and air above the volcano. Any boat passing over Kick 'em Jenny during an explosive eruption would be in danger. In addition, there is another, hidden hazard which is ever-present at Kick 'em Jenny, namely the possibility of lowered water density above the volcano. It is extremely likely that considerable amounts of volcanic gas escape from Kick 'em Jenny, even in quiet times between obvious eruptions. If these bubbles become concentrated and the water density drops, any boat entering into the area will experience a loss of buoyancy and may even sink.
Happy sailing (preferably not directly over Kick 'em Jenny)!
Dr. Jan M. Lindsay is a Volcanologist with the Seismic Research Unit of the University of the West Indies at St. Augustine, Trinidad & Tobago. She and her husband sail out of Trinidad aboard their yacht S/Y Strelasund.
More information and further updates on Kick 'em Jenny are available from www.uwiseismic.com. If anyone observed anything unusual in the sea near Kick 'em Jenny on December 4, 2001 or in the days following the eruption, Jan would love to hear from you at tel (868) 662-4659, fax (868) 663-9293 or firstname.lastname@example.org. Thank you!
Copyright© 2002 Compass Publishing