Aug. 16, 2003 – Explanations of the mysterious venting of hot material from two holes in the earth in the Peterborg area of St. Thomas continued to elude V.I. officials and University of the Virgin Islands investigators on Saturday.
On Friday around 1 p.m., V.I. residents Tim Handfield and his family and their guests visiting from Rhode Island came upon what they thought to be a small volcanic eruption on Peterborg peninsula. They reported the event and took rock samples to the V.I. Fish and Wildlife Division along with a videotape of what they observed.
Officials from that division, the Police Department and the V.I. Territorial Emergency Management Agency went to the scene and examined the area, taking photographs and interviewing the witnesses. UVI scientists also responded, obtaining samples that they could analyze in their laboratory.
Unlike Montserrat and the islands south of Saba, the northeast Caribbean islands westward from Anguilla are known to have volcanic origins, but with no volcanism at all occurring for millions of years. The recent publication "The Geology of St. John, U.S. Virgin Islands" by Douglas Rankin puts the age of the youngest igneous rocks in the U.S. Virgin Islands at 24 million years. Most of the islands of the Eastern Caribbean, on the other hand, are much younger and have dormant or active volcanoes.
Tests to determine this time frame, according to UVI chemist Stan Latesky, would not have been Carbon-14 dating, which can date back approximately 50,000 years, but rather krypton-argon dating.
At the Peterborg site, Latesky and UVI physicist Roy Watlington noted the presence of small, smooth glass spheres along with larger fragments of glass welded to charred rock. Some of the pieces were up to 20 feet away from the vent holes. One 10-inch sample, pictured above, looks as if 3 inches of it had been melted and left with a glassy surface.
Reached at home by the Source Saturday night, both scientists said they had performed "very preliminary" analyses of some of the samples and found them resistant to Bunsen burner flame. "They did not burn or melt at those temperatures, somewhere around 500 degrees Celsius, or 900-930 degrees Fahrenheit," Latesky said. "They started to glow. We believe the glassy samples are really molten rock turned to glass."
Of several possibilities considered, Latesky said, hydrocarbon underground as a source of the phenomenon is "pretty well ruled out," because the items simply did not burn. Whatever melted the materials was hot enough to "melt" igneous rock — an example would be an acetylene torch, which can reach above 1,200 degrees Celsius.
Watlington offered this theory: "We visualize that there had been a jet of very hot gas, with no lava or solid material, penetrating upwards and creating its own glass tube by melting solid rock, then firing some of the melted material into the air." Pieces of the tube were removed and taken to the UVI laboratory where they are being further analyzed.
Watlington noted that the densities of the glassy samples and of the charred rock are very close and that both values are what would be expected of surface rocks in that geological setting.
VITEMA's deputy director, Clayton Sutton, reached by telephone Saturday, stressed that the assessment is ongoing, and no final conclusions have been reached. He said the consensus of all investigators is that the assistance of other professionals will be sought.
Two of those professionals are the director of the Puerto Rico Seismic Network, Christa Von Hillebrandt-Andrade, and Dr. Haraldur Sigurdsson, vulcanologist at the University of Rhode Island. Both are scientifically familiar with the Virgin Islands area and have lectured on St. Thomas and St. John.
As far as what lies ahead in the investigation, Latesky mentioned testing of the material to determine, for one thing, whether it is silica-based or alumina-based. He emphasized that he is not a geochemist or a geologist and said he will defer to experts.
Everyone contacted stressed that the continued investigation merits great caution. "Before we disturb the soil in the area in any way," Watlington said, "we should establish whether or not there were ever military installations in the area."
There is a chance, he continued, "that something was buried there that could present a hazard to someone digging around the vent holes."
Latesky agrees. "Whatever melted that material was extreme," he said. Even something like rocket fuel is a possibility. "What we saw is something I've never seen on St. Thomas," he said. "It's not natural. We must be very cautious."
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