 In 2000 , glacier caves were discovered on the then @-@ smooth glacier surface . Many of these glacier caves were big enough to explore , like the glacier caves on the summit of Mount Rainier . Most of the glacier caves were located near the 1980s lava dome , where hot steam and volcanic gas emissions from hidden fumaroles on the crater floor or lava dome melted holes in the young glacial ice . About 7 @,@ 900 feet or 2 @.@ 4 km of underground caves and passageways in the glacier were mapped and studied . 
