Mount St. Helens, Washington State, USA, is characterized by a 2 x 3.5 km horseshoe-shaped and north-facing crater and hosts one of the last expanding glaciers in the Cascade Volcanic Arc, Crater Glacier. First observed in 2012, a new and extensive system of glaciovolcanic caves has developed around the 2004-2008 Lava Dome inside the Crater Glacier. Field studies have documented the cave characteristics via photography and tacheometric survey methods repeated from 2014-2019. Climatologic measurements reveal that sub-glacial fumarole activity leads to large-scale cave complexes, sometimes several hundred meters long. These allowed comparisons of passage extent and volume to be made and gave us a unique opportunity to observe their genesis over time. Ten distinct caves have been discovered in a circumferential pattern surrounding the 2004-2008 Lava Dome. The caves comprise a combined length of 2,232.3 m, the three most significant ones reaching more than 400 m each. Changes in the output of individual fumaroles which have melted the passages have also contributed to the appearance and disappearance of subglacial rooms and marginal dendritic passages which typically orient to entrances along the rock/ice interface. Over time the caves have demonstrated significant morphological changes. Multiple caves demonstrated increases in length and volume over the study period, along with changes to internal morphology. Caves located on the east and west arm of the glacier are additionally influenced by glacier movement and a fast flow rate which contribute much to morphology changes. Resurveys of cave passages over multiple years have revealed the dynamic nature of the systems, which are not necessarily in balance with the geothermal heat release. We expect that the overall growth of the cave systems will continue as long as an equilibrium of snow accumulation and ablation is reached or changes in volcanic activity occur. The newly formed glaciovolcanic cave systems on Mount St. Helens offer a rare view into the internal workings of a glacier and can lead to a better understanding of how glaciers and active volcanoes interact.