Gaseous emissions at the site of the Delphic Oracle: Assessing the ancient evidence

Gaseous emissions at the site of the Delphic Oracle: Assessing the ancient evidence

To the Editor:

In a recent paper by Foster and Lehoux (1), the two authors comment on the results of our team's study of evidence for gaseous emissions at the site of the ancient Delphic Oracle in central Greece. Judging from their comments, Foster and Lehoux appear to be insufficiently familiar with the ancient sources, with scientific method, and with the site of Delphi itself. Their paper attempts to reassert the orthodox position of 20^th century classical scholars, who have routinely maintained that there is no truth to the ancient tradition of unusual geological phenomena and activity at the oracle site.

With regard to the ancient sources, it is misleading for them to state that “almost no ancient sources” mention the fissure and the intoxicating pneuma (a Greek term that can mean gas, wind, breath, or vapor, depending upon its context) in the oracular temple. Only a small fraction of ancient literature survives: there is, for example, only one reference to the Parthenon at Athens in the entire literature of the 5^th century BC, when the temple was constructed. What counts is not quantity but quality, and in the case of the Delphic Oracle we are fortunate to have three essays by the Greek writer Plutarch, who served as priest at Delphi for many years and was an eye-witness to the oracular sessions. Plutarch makes it clear that from time to time, there was a sweet-smelling emission from the adyton or oracular chamber. He attributes the weakness of the emission in his own time to such geological activity as earthquakes that sealed up the vents in the rock, or limited amounts of the “vital essence” in the rock itself. Plutarch records routine oracular trances, after which the woman who spoke the oracles appeared like a runner after a race or a dancer after an ecstatic dance. And he contrasts these with extraordinary cases in which the woman raved and flung herself about in a delirium. Throughout his writings, Plutarch makes it clear that the oracle's power was believed to derive from a physical, geological source.

Foster and Lehoux also misunderstand the process of standard scientific method, which starts with a hypothesis and then tests the hypothesis against data. This may appear “circular”, but it is the opposite of circular reasoning, since the hypothesis is not accepted unless it is confirmed by the evidence. In the case of our research, we tested the hypothesis that ancient reports about the oracle were accurate by conducting geological and archaeological surveys at Delphi and analyzing gases in ground water from modern springs at and in travertine rock laid down by the springs at the time the oracle was active. The data confirmed that the rock beneath the temple was fractured by geological faults, and that the spring water, ancient and modern, contained intoxicating light hydrocarbon gases in higher than atmospheric concentrations. These findings confirmed the accuracy of the ancient tradition, which Foster and Lehoux wish to deny.

A serious error occurs in Foster and Lehoux's statements about ethylene. They use a figure of 2.2 for the atmospheric destruction of ethylene, the sweet-smelling hydrocarbon which we identify with Plutarch's sweet-smelling emission. This short time, according to them, would not allow sufficient concentrations of ethylene to develop in the temple crypt. However, if they had read their own source with attention, they would have discovered that the process is photochemically driven and depends on sunlight (2). There was no sunlight in the depths of the temple where the adyton was located, and therefore ethylene could have lasted considerably longer as a free gas.

It is not surprising that ethylene was not detected in the travertine rock around the temple. Ethylene is highly reactive. Rather than surviving through the centuries, the original ethylene would be chemically altered to form ethane and/or methane, also intoxicating hydrocarbons, which were found in the travertine.

A second geological study of the Delphic Oracle site was published by Etiope et al. in Geology 2006 (3). A team of five Italian and Greek geologists confirmed the presence of active faults and gaseous emissions at Delphi. They suggest that benzene was the sweet smelling gas that triggered the oracular trance. Whatever the exact identification of the gas may be, their research supported the conclusion that intoxicating hydrocarbons formed the “active ingredient” in the pneuma described by the ancient writers. Additionally, within the last year a study by a team of archaeologists and geologists has documented a second oracular shrine at a Temple of Apollo in Hierapolis, Turkey constructed by the Greeks directly over an active geological fault with a gaseous vent from a cavern (the Plutonion) (4). Again ancient writers linked these toxic emissions to the religious cult. Ground penetrating radar has identified a previously unknown man-made subterranean chamber under the temple on the fault line, interpreted to be an entrance to the cavern. While in the case of Hierapolis the gaseous vent emits carbon dioxide, it again demonstrates the ancient tradition of locating oracular buildings and temples of Apollo on specific geological phenomenon. Foster and Lehoux are also unfamiliar with basic geology and plate tectonics. Plutarch claimed that the emission had weakened through time. Natural changes in the flow rate of springs and associated gases are a common phenomenon, especially in highly seismic areas. Emission rates following earthquakes remain high for years and slowly decrease over time. In any case, the permeability and porosity of fault zones in limestone complexes are reduced by the formation of calcite and travertine crusts laid down by springs. Spaces are then frequently opened up again as a result of vibrations caused by strong earthquakes elsewhere in the tectonic zone. The recurrence rate for quakes with magnitude around 6 in the Corinth rift zone has been estimated at between 100 and 150 years. Therefore, Delphi has been shaken repeatedly through the centuries with related consequences for gas emissions.

For a full understanding of ancient writers, it is important to visit and study the sites that they described. For example, Foster and Lehoux make much of the small amount of water currently flowing from the Kerna spring above the temple. If they were familiar with Delphi, they would see that while the water presently seeps from a minor crack and collects in a small reservoir, its flow has been significantly reduced due to a major diversion that has affected all springs along the Kerna fault. In recent years, local engineers have drilled several holes and constructed reservoirs in the Kerna fault zone above the oracular site. From there, the water that used to flow through the sanctuary is now piped to modern Delphi. Additionally, the flow in the past was clearly greater than today as evidenced by the existence of thick travertine curtains that cover the retaining wall beside the temple. These deposits indicate clearly that the volume of groundwater and associated gases was significantly larger in the past.

The archaeological evidence of the temple itself shows that the design and layout was adapted to accommodate certain geological features. The asymmetrical inner space of the temple provided for an alcove on the southern side where a spring must have emerged, since a series of tunnels and conduits was constructed through the massive stone foundations to drain the spring water out of the adyton. The ancient architects would not have constructed such a feature if it had not been necessary.

In conclusion, ancient authors referred to geological phenomena at the site of the Delphic Oracle – a fissure, a spring, and a gaseous emission – and two recent scientific surveys including our own have demonstrated that these features exist. In our view, the burden of proof now rests with the detractors of Plutarch and the other sources, rather than with those who take their testimony seriously.