Ice level changes from seasonal to decadal time-scales observed in lava tubes, Lava Beds National Monument, NE California, USA

Abstract

Numerous lava tubes host seasonal or perennial ice accumulation in the Lava Beds region. Systematic ice level monitoring has been conducted for eight ice caves since 1990, and four other ice caves were added to the monitoring program during recent years. Cave names are used for publically advertised ice caves, and cave codes are used to help protect ice resources of the other eight monitored ice caves. Monitoring data has revealed that the seasonal cave ice phenology can be characterized by autumnal ice level low-stands of ice floors in the lava tubes. Regarding the multiannual evolution, both positive and negative ice mass balance periods were detected during the past 23 years. Balanced glaciation characterized the lava tubes over the early 1990s. Positive mass balances were reported for many caves from the late 1990s. Ice levels are still stable in Skull Ice Cave and U-200. Severe ice loss, however, has characterized the evolution of ice deposits in the other monitored caves. Major ice loss started in 1999 in Merrill, C-270, and M-470 ice caves, while not until 2003 in L-800. The recent rapid ice melt resulted in total ice loss for some caves. The perennial ice disappeared, for instance from M-470 and M-475 by 2005 and from Merrill Ice Cave by 2006.