普若岗日冰原及其小冰期以来的冰川变化

Puruogangri Ice Field and Its Variations Since the Little Ice Age of the Northern Tibetan Plateau

普若岗日是藏北高原最大的由数个冰帽型冰川组合成的大冰原 .冰川覆盖面积 42 2 5 8km2 ,冰储量为 5 2 5 15 3km3 .冰川雪线海拔 5 6 2 0～ 5 86 0m .冰原呈辐射状向周围微切割的宽浅山谷溢出 5 0多条长短不等的冰舌 ,最大的可伸至山麓地带 ,形成宽尾状冰舌 .在一些下伸较低的冰舌段 ,形成有许多冰塔林 ,以雄伟壮观的连座冰塔林和雏形冰塔林为主 .在东南部一些冰舌段雏形冰塔林的上部 ,分布着奇特的新月型雪冰丘和链状排列有序的雪冰丘 .小冰期以来 ,普若岗日的冰川呈退缩趋势 .环绕冰舌分布的冰碛序列 ,在北部和东南部普遍可区分出 3道 .对比研究认为 ,分别属于小冰期 3次寒冷期冰进的遗迹 .而西部小冰期冰川作用的范围较小 .按小冰期最盛时的规模量测当时的冰川面积 ,和现在相比该时段内冰川面积减少了 2 4 2 0km2 ,当时冰川面积比现在大 5 7% .由此引起的冰川资源的减少为 3 6 5 83km3 ,相当于 36 5 83× 10 8m3 的水量 .在普若岗日西侧 ,小冰期后期至 2 0世纪 70年代 ,冰川退缩了 2 0m ;70年代至 90年代末 ,冰川退缩了 40～ 5 0m ;平均 1 5～ 1 9m·a-1;1999年 9月至2 0 0 0年 10月 ,退缩 4～ 5m .明显反映出逐渐加剧的变化趋势 .和其它地区相比较 ,普若岗日冰原变化比较小 。

Puruogangri ice field is the largest ice field in the Northern Tibet Plateau composed of several ice caps, with an area of about 422^58 km 2 and a volume of 52^5153 km 3, %ELA% ranging from {5 620} to {5 860} m a.s.l. More than 50 ice tongues with different lengths extend around to wide and shallow valleys, of which the longest one has a wide terminus reaching the foothill, In the area with lower tongues, there are many ice pyramids, mainly in an initial stage and with connected bases. Since the Little Ice Age the ice field has trended to retreat. There are three moraines around the tongues in the north and southeast. They belong to three cold periods when glacier advanced. At those time, less advance presented in the west. From the Little Ice Age up to now, glacier area decreases 24^20 km 2, 5^7% of the original area, equivalent to 3^6583 km 3 of ice loss. In the west it is found that the glacier retreated by 20 m from the post Little Ice Age to the 1970 s, and 40～50 m from the 1970 s to the end of the 1990 s, with an average rate of 1^5～1^9 m5a+{-1}. It retreated 4～5 m from September 1999 to October 2000, showing an intensified retreating. However, the Puruogangri Ice Field is relatively stable as compared with other glaciers.