| Title | POST-DEPOSITIONAL ALTERATION OF SILICEOUS SINTER NEAR OLD FAITHFUL GEYSER, YELLOWSTONE NATIONAL PARK, USA |
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| Authors | B. Lynne, G. Smith, H. Heasler, C. Jaworowski, I. Smith, D. Foley and D. Sahdarani |
| Year | 2017 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Yellowstone National Park; Siliceous Sinter; Shallow Hydrology, Hydrothermal Alteration, Ground Penetrating Radar, Scanning Electron Microscopy, Computerised Tomography, X-Ray Diffraction |
| Abstract | Siliceous sinters are hot spring rocks that form as opal-A silica precipitates and accumulates from discharging alkali chloride hot springs, as the water cools to <100 °C. In a thermal setting it is common for hydrothermal conditions to change over time. Such changes are recorded in the sinter as alteration over-prints. The shallow subsurface conditions underneath the siliceous sinter terrace surrounding Old Faithful Geyser, Yellowstone National Park, USA, was investigated for evidence of post-depositional alteration. A subsidence bowl was observed on the sinter terrace to the east, while no subsidence was visible on the sinter terrace to the west of Old Faithful Geyser. However, both areas displayed localised sites of steam discharging through the sinter terrace. To investigate the shallow subsurface conditions we used the multi-technique approach of Ground Penetrating Radar, Scanning Electron Microscopy, Computerized Tomography and X-Ray Diffraction. Our results revealed the presence of acidic steam condensate zones in the shallow subsurface, beneath the sinter terrace in both areas, providing evidence that the boundary of the hydrothermally-altered ground extends beyond that which is visible at the surface. Identifying these zones is important as this type of hydrothermal alteration weakens the sinter, providing ideal conditions for subsidence. The combination of these non-invasive techniques has proven successful in mapping potential subsidence sites and in tracking shallow heat migration pathways. |