Estimating and managing blowout risk during access to subglacial Antarctic lakes

As Antarctic subglacial lake research progresses to in situ exploration an important topic is the
lake’s probable gas concentration. Depending on hydrological setting, subglacial lakes may contain large
amounts of dissolved gas or gas trapped within clathrates. Consequently, access can be potentially
dangerous due to the risk of blowout where depressurization could lead to high-speed ejection of water and
gas from a borehole. We present a structured approach to assess the blowout risk in subglacial lake
exploration. The approach integrates a generic event tree, applicable to open and closed hydrological
systems, with site-specific expert judgment incorporating rigorous probabilistic formulations. The
methodology is applied to a motivating example: Ellsworth Subglacial Lake. Judgments elicited through
a formal process were provided by five experts with 88 years combined experience that, after aggregation,
gave a median risk of blowout of 1 in 2186 with a lower quartile of 1 in 3433 and an upper quartile of 1 in
1341. This approach can be applied to any subglacial lake given a modicum of knowledge on its
hydrological setting, as uncertainty can be captured through the elicited judgments. Additionally, the event
tree analysis informs blowout mitigation strategies to reduce risk of injury or death.