mountain high-elevation mountain On Earth, mountains in this category cross the atmospheric oxycline above which oxygen concentrations fall below the physiological tolerance threshold of most humans. Note that the threshold elevations are inconsistent between the various reports which list this classification: while some have overlapping thresholds, others are non-overlapping. The latter model is used in ENVO for coherence and to adhere to the Kapos et al. 2000 reference. A mountain which has a maximum elevation greater than 2500 metres above sea level. https://orcid.org/0000-0002-7556-2097