山岳氷河の質量・水収支の経年変動

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Meteorological and hydrological data for a drainage basin of a mountain glacier, the GulkanaGlacier, Alaska, monitored by U. S. Geological Survey (USGS) for more than 40 yrs, are correctedand retrieved. Interannual variations of daily mean air temperature and daily precipitation nearthe glacier and daily runoff rate at a proglacial stream averaged over the ablation period (June toSeptember) indicate that the increasing rates of 1968－2010 and 1985－2010 are 0.012 ℃/yr and0.014 ℃/yr, 0.024 mm/yr and 0.041 mm/yr, and 0.092 mm/yr and 0.25 mm/yr, respectively. Thus,the runoff rate and precipitation tend to increase greatly in the recent years. The daily glacier-meltrunoff rate averaged over the ablation period was obtained on the assumption of zero englacialwater storage change over the period. As a result, the glacier-melt runoff rate exhibits the linearrelationship with the daily mean air temperature near the glacier. The summer ablation of the glacierwas larger than the winter accumulation in many years, consequently indicating that the netmass balance is negative in almost all the years. Especially since 1988, the net mass balance is negative in any years. The tendency of greatly negative cumulative net mass balance since 1988suggests that the glacier thickness become zero in ca. 2160. Meanwhile, the glacier area tends todecrease greatly and linearly since 1993 at the rate of -0.18 km2/yr. This indicates that the glacierarea would be zero in ca. 2096. The large decrease of cumulative net mass balance since 1980’sis common to the three glaciers, Gulkana, Wolverine and South Cascade, monitored by USGSsince 1960’s. The decreasing rate of glacier thickness in 1980’s to 2004 is -0.74 m/yr for GulkanaGlacier, -0.78 m/yr for Wolverine Glacier, and -0.71 m/yr for South Cascade Glacier, thusshowing the similar tendency in thinning.
2012-03-19

山岳氷河の質量・水収支の経年変動

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