青藏高原发现大型冻胀丘群

在青藏高原黄河源地区多格茸盆地内发现大型冻胀丘群,这些冻胀丘外观多呈穹窿状,有些呈脊状、新月状.盆地内的冻胀丘隆起高度多在3~6 m,最高不超过10 m,水平扩展范围数十米到上百米,最大超过300 m.冻胀丘在盆地内密集分布,众多小型湖塘嵌于其中,分布密度估计5~8个·km^-2,局部区域内可达10个·km^-2以上.从外观看,多数冻胀丘形态较完整,但有的已经部分塌陷,有的几乎完全塌陷,不同塌陷阶段的冻胀丘在盆地内均有发现.冻胀丘顶部钻孔岩芯揭示高含冰地层从丘顶以下5 m左右一直延续到20多米,局部发育厚层地下纯冰层,厚度可达2 m以上.根据外观形态、地下冰类型判断,这些多年生的冻胀丘属冰土丘(lithalsa),和常见的冰核丘(pingo)有所区别.初步判断,这些冻胀丘形成于全新世大暖期以后的新冰期时期.多格茸盆地冻胀丘群的发现对现行的工程建设及工程建筑物的运营安全、区域古环境、流域水文等方面的研究都具有重要意义.

Discovery of large frost mound clusters in the source regions of the Yellow River on the Tibetan Plateau

Frost mounds in a large cluster are identified in Duogerong basin in the source regions of the Yellow River on the Tibetan Plateau by field investigation in the winter of 2012, which was previously regarded as dunes or kames. The majority of these frost mounds are elliptical shapes in plane, together with ridge and crescent shapes. They are normally 3~6 m in height(less than 10 m) and extend from dozens of meters to hundreds of meters(not more than 300 m). Frost mounds spread densely in basins; on average, there are 5~8 mounds per km²(locally up to 10 mounds per km²), embedded with small ponds and lakes. Most frost mounds keep intact shapes, but partially or completely collapsed ones can be seen because of the ground ice cores thawing. Frost mounds in different collapsing stages are found in the depressions of the basin. The boreholes at the top of mounds reveal that there are ice layers between the depths from 5 m to 20 m, partly with pure ice layers of 2 m or more in thickness. From appearance and type of the ground ices, the frost mounds are identified as lithalsas rather than pingos. Preliminary investigation indicates that these lithalsas are formed during Neoglaciation after Magathermal in Holocene. Discovery and identification of the frost mounds in Duogerong basin may contribute to the construction and safe operation of existing engineering projects and infrastructures and to the researches of regional paleo-environment, hydrologic conditions and periglacial landforms.