The Seismic Research Center (SRC) of the University of the West Indies has issued an Orange alert (3 of 4) for the underwater volcano Kick 'em Jenny on July 23, 2015, due to strong and continuous seismic signals recorded from 05:25 to 07:00 UTC today. Grenada, as well as St. Vincent and the Grenadines, Barbados and Trinidad & Tobago are particularly on alert as eruption may begin with less than 24 hours notice.

Signs of elevated seismicity began on July 11 and continue to present, SRC said.

Director of the Coastal Zone Management Unit in Barbados, Dr Lorna Innis, reassured residents of the island that the probability of a tsunami following the possible eruption of Kick ’em Jenny was low – but not non-existent. The probability of tsunami generation from underwater volcanoes increased the closer the volcano’s dome was to the surface of the sea, unlike Kick ’em Jenny, which is believed to be located at a depth of 180 m (590 feet) under water. (AGM)

Orange alert issued by SRC today means eruption may begin with less than 24 hours notice. The Center recommends that governments of Grenada, St. Vincent, Barbados and Trinidad & Tobago should advise residents of evacuation routes, and put transportation on standby to facilitate evacuation in the event of a tsunami. Local radio stations are placed on alert and public is asked to listen them continuously and visit SRC website if possible.

An eruption, or increased activity, is particularly dangerous for marine vessels, since the gases released from the volcano can lower water density and cause sinkage. Therefore, all shipping should stay 1.5 km (0.93 miles), and non-essential shipping should stay 5 km (3.10 miles) from the summit of Kick 'em Jenny.

Vertically exaggerated SeaBeam image of Kick 'em Jenny and newly identified craters and domes discovered in March 2003. Credit: NOAA and SRU.

The last eruption of this volcano (minor) began on December 4, 2001 and ended on December 8. The first signs of unrest occurred in October when a slight increase in seismicity was recorded near the volcano. The eruption began when a burst of activity started at 10:00, peaking at 15:00 UTC.

Following a short lull, activity again increased and culminated in bursts of T-phase signals (acoustic waves generated from an earthquake or underwater explosion that travel through the ocean). The signals were detected between 23:18 on December 4 and 02:31 UTC on December 5 and were interpreted as explosions associated with a submarine eruption. There was no observed activity on the sea surface. The largest earthquakes associated with the eruption were felt in northern Grenada, ~ 8 km (~5 miles) to the S.

After December 7, seismicity returned to background levels. During the eruption the Alert Level was raised from Yellow ("volcano is restless") to Orange ("highly elevated level of seismic and/or fumarolic activity") and returned to Yellow on December 8.

Geological summary

Kick 'em Jenny, a historically active submarine volcano 8 km (5 miles) off the north shore of Grenada, rises 1 300 m (0.8 miles) from the sea floor. Recent bathymetric surveys have shown evidence for a major arcuate collapse structure that was the source of a submarine debris avalanche that traveled more than 15 km (9.3 miles) to the west.

Bathymetry also revealed another submarine cone to the SE, Kick 'em Jack, and submarine lava domes to its south. These and subaerial tuff rings and lava flows at Ile de Caille and other nearby islands may represent a single large volcanic complex.

Morphology of Kick 'em Jenny, as revealed by a multi-beam survey by the NOAA Research Vessel Ronald H. Brown in March 2002 (N is toward the top; for approximate scale, the sub-circular summit crater is about ~ 300 m in diameter). The survey showed that the volcano's smaller, modern, active cone sits nested within a larger U-shaped depression that wraps completely around the cone's E side and opens toward the W. This larger depression presumably formed by slope failure and generated a W-directed debris avalanche that appears to lie within a marginal, confining levee. Credit: NOAA.

Numerous historical eruptions, mostly documented by acoustic signals, have occurred at Kick 'em Jenny since 1939, when an eruption cloud rose 275 m (0.17 miles) above the sea surface. Prior to the 1939 eruption, which was witnessed by a large number of people in northern Grenada, there had been no written mention of Kick 'em Jenny. Eruptions have involved both explosive activity and the quiet extrusion of lava flows and lava domes in the summit crater; deep rumbling noises have sometimes been heard onshore. Historical eruptions have modified the morphology of the summit crater. (GVP)

Update:

Kick 'em Jenny activity decreases, alert level lowered to Yellow - Eastern Caribbean

Featured image credit: NOAA.