Geophysical study of underground cavities near the Cueva de la Orquídea Park, Xalapa, Veracruz, Mexico

Abstract

The Cueva de la Orquida (Orchid cave) is one of the tourist attractions in Xalapa. It is located in a public park with the same name in the middle of the city. However, this "cave" is actually part of a system of lava tunnels that are formed when low-viscosity lava (commonly basaltic) cools on contact with the underground and the atmosphere, but continues to flow inside. Most of the center of Xalapa is built on top of these basaltic lavas that underlie the Macuiltépetl cinder cone. The location of the underground lava tunnels is unknown; only occasionally collapses are reported in the urban area, due to the collapse of some underground cavities, as well as being discovered when digging before starting construction. In this study, two non-invasive geophysical techniques are used within the Park area, as well as on unpaved streets in the vicinity of the Park. The results of the gravimetry and georadar study not only make the previously known large cameras (3 connected) visible, but also reveal their continuity to the East, just below the houses surrounding the park. It is considered important to continue with the studies to locate the cavities closer to the surface and/or more voluminous to identify areas potentially in danger of collapsing, adapt construction plans, among other mitigation measures.