This spaceborne radar image shows the Ruiz-Tolima volcanic region in central Colombia, about 150 kilometers 93 miles west of Bogata. Space Radar Image of Ruiz Volcano, Colombia Part of the variance in the geodetic data results from real but noncumulative deformation that may in part be pressure-buffered by a fairly large geothermal water-gas mixture for which abundant physical evidence exists This lack of significant intrusive activity agrees with the surprisingly low seismic energy release under Ruiz and makes direct degassing of a large batholith an improbable explanation of the large sulfur flux to date at Ruiz. Thus, little, if any, magma intruded above 5 km beneath the summit during or after the 13 November 1985 eruption.

The data collected from the geodetic networks have higher than normal variance but demonstrate that little or no cumulative deformation of Ruiz occurred from October 1985 through March 1988. Stations established to detect instability of the summit ice cap after the eruption were discontinued in early 1986. In addition, 4 telemetered tiltmeters provided the capability of detecting, in real time, the fairly rapid ascent of much smaller magma bodies. Geodetic monitoring resumed 1 week after the eruption and, by April 1986, included 11 tilt-leveling stations, 38 EDM lines, and 7 short leveling lines - a network capable of detecting emplacement or movement of magma volumes as small as 3 MCM (3 ? 106 m3) to a depth of 2-3 km (using a point-source model), 10 MCM to 7 km, 50 MCM to 10 km, and 200 MCM to 15 km beneath Ruiz. However, the data require that the magma source of the devastating eruption was either deeper than 7 km or, if shallow, recovered the same volume and position within one week of the eruption.

The late start in geodetic monitoring, limited number of stations in the pre-eruption network, and inconsistent patterns in the observed deformation limit conclusions about intrusive activity in the months and weeks prior to the eruption. Tryggvason, E.ĭeformation studies began at Nevado del Ruiz 23 days before the devastating 13 November 1985 eruption, at least 12 months after precursory seismicity and fumarolic activity began. Deformation monitoring at Nevado del Ruiz, Colombia - October 1985 - March 1988īanks, N.G.

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