Additional Report for Town of Jerez

False Report of New Volcano

Near the Town of Jerez, Zacatecas, Mexico

~22.4°N, ~103.0°W


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05/1997 (BGVN 22:05) Rumors of new volcano prove false: methane combustion implicated


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05/1997 (BGVN 22:05) Rumors of new volcano prove false: methane combustion implicated

Although mid-May speculations suggested that a new volcano might be developing in the SE part of the State of Zacatecas, the incident has been attributed to methane combustion unrelated to volcanism. The event took place near the town of Jerez, ~50 km SW of Zacatecas city. Hugo Delgado received a video made by local residents, asked officials about the event, and provided the following report.

"The place where this phenomena is happening is a flat area (a square area [~20 m on each side]) where the ground is smoking (combustion-like blue smoke). There are several cracks on the ground and inside the cracks the earth looks reddish and hot. The people who sent me the video show how a piece of wood burns [when] they put it inside the crack. The area was isolated from the curious people (crowds of families who want to see what is happening visit the place) [by] digging a furrow around the hot site and posting policemen in order to [prevent] children [from falling] into the hot cracks.

"People from the University of Zacatecas and from the SEMARNAP (Ministry of the Environment, Natural Resources, and Fisheries) have visited the area and concluded that microbial activity on concentrated organic material in the area has produced methane and this started to burn since the beginning of May. Burning of methane has [caused] the ground to glow. According to their report, no deformation of the ground has been detected, nor [were] ashes or sulfuric odors detected during their visit. Samples taken from the ground were chemically analyzed [revealing] mainly organic material in them. This kind of [incident] has occurred before in other [parts] of Zacatecas, according to SEMARNAP.

"[It] seems that somebody (unidentified, but according to the local people, it was a retired scientist [transporting] equipment) came to the region to see the phenomena, and commented that it was the birth of a volcano. Thus, the inhabitants became alarmed. Local newspapers have also published that methane is burning there according to the researchers of the University of Zacatecas.

"Officials from the National Center for Disaster Prevention (CENAPRED) knew about this event, and have received the reports from SEMARNAP and the University of Zacatecas. This has been treated not as a volcanic problem but [an] environmental [one].

"A year ago, there was a similar event in the region. Carlos Gutierrez from CENAPRED visited the zone in order to deploy seismic equipment to observe this event. It was determined that organic material (sedimentary carbon[aceous] deposit[s] in a lacustrine environment during the Pleistocene) was burning underground after the local people incinerated dry grass (a common practice in Mexico to fertilize the land before the rainy season)."

Luca Ferrari provided geological insight into the area. It is on the E flank of the Sierra Madre Occidental, a huge mid-Tertiary volcanic pile related to subduction of the Farallon Plate. Volcanic rocks in the area include extensive silicic ashflow tuffs of late Oligocene to early Miocene age; these are sometimes capped by small volumes of andesitic and basaltic lavas ~20 Ma old. The incident took place more than 200 km N of the active volcanic arc (the Mexican Volcanic Belt, related to the ongoing subduction of the Rivera and Cocos plates). Quaternary intra-plate basalts are absent within a 200 km radius of the site of the incident. From a tectonic point of view, the village of Jerez lies at the N end of the Tlaltenango graben, which formed during Basin and Range extension in the early Miocene. Tectonic activity appears to have slowed since then and no Quaternary faulting is reported in the region.

Information Contacts: Hugo Delgado, Instituto de Geofisica, U.N.A.M.Circuito Cientifico, C.U. 04510, Mexico D.F., Mexico (Email: hugo@tonatiuh.igeofcu. unam.mx); Luca Ferrari, Instituto de Geologia, UNAM, Apdo. Postal 376, 36000 Guanajuato, Gto., Mexico (Email: luca@servidor.unam.mx).