Using ground penetrating radar, scanning electron microscopy and thermal infrared imagery to document near-surface hydrological changes in the old faithful Geyser area, Yellowstone National Park, U.S.A.

•Changes in the shallow subsurface hydrology in the Old Faithful Geyser Area are documented using GPR, SEM, and TIR.•Sinter from (1) unaltered terraces, (2) partially-altered terraces, (3) highly-altered terraces were analysed.•The alteration is driven by acidic steam condensate overprinting the sinter to various degrees.•This subsurface process has resulted in the formation of subsidence bowls in the Old Faithful Geyser Area.