甘肃省舟曲特大泥石流的遥感影像特征及古泥石流遥感识别的地质意义

HIGH-RESOLUTION REMOTE SENSING IMAGERY CHARACTERS OF ZHOUQU EXTRA-LARGE-SCALE DEBRIS FLOW AND GEOLOGICAL SIGNIFICANCE OF IDENTIFYING ANCIENT DEBRIS FLOWS DIRECTLY BY USING REMOTE SENSING METHODS IN GANSU PROVINCE

2010年舟曲特大泥石流是舟曲地区第四纪以来泥石流最新暴发期内强烈活动的体现,所造成的人员伤亡及财产损失堪称世界泥石流灾害史之最。准确分析该地区泥石流的空间分布规律及预测未来泥石流暴发时间可为泥石流的防灾救灾提供科学的依据,其首要任务就是利用一种先进技术对不同时期的泥石流堆积物的空间分布进行快速、准确的识别。遥感技术具有数据获取量大、空间分辨率高及快速等方面的独特优势,可在舟曲特大泥石流及不同时期古泥石流堆积物识别中发挥重要作用。在高分辨率的航空遥感影像上,舟曲特大泥石流具有明显的光谱特征,可用于准确圈定泥石流灾害的范围;泥石流堆积物在沟谷两侧形成的侧碛堤及在堆积区末端形成的扇形地等形态特征也是识别泥石流的另一个重要标志。舟曲县城东南瓦厂村南及马莲坪村西南白龙江支流沟中的垄岗状堆积物和沟口处的扇形地堆积体在光学遥感影像上具有典型的古泥石流堆积的形态特征,雷达遥感的后向散射系数对比分析和对堆积物剖面的沉积特征分析也证明古泥石流的存在。研究结果表明,通过多期次、多空间分布的现代和古泥石流的对比,不仅可以揭示舟曲地区第四纪以来泥石流发育历史并间接反映地质尺度上气候变化特点,还可为未来泥石流的易发性分析提供数据支撑,因此泥石流堆积物的遥感直接识别具有重要的地质意义。

Zhouqu extra-large-scale debris flow in 2010 was the newest action since Quaternary in Zhouqu area and caused the severest casualties and property losses in the history of the world＇s debris flow hazards.It could provide scientific bases for debris flow disaster relief and prevention to analyze the spatial distribution of debris flow deposits and forecast time of occurrence of debris flows in the future accurately.The primary task was to identify the spatial distribution of debris flows in different periods quickly and accurately by using an advanced technology.Remote sensing technology has the unique advantage in a large amount of data acquisition,high spatial resolution and quickness and can play an important role in identifying Zhouqu extra-large-scale debris flow and ancient debris flow deposits in different periods.On the high-resolution aerial remote sensing image,Zhouqu extra-large-scale debris flow had obvious spectral characteristics which could be used to accurately delineate the scope of debris flow disaster.Accumulation forms including lateral moraines on both sides of the valley formed by the debris flow and the fan at the terminal of the accumulation area were other identification signs.On the optical aerial images （0.2m）,the fans in the outlet of the tributaries of Bailongjiang River which lie to the south of Wachang Village,and the south-west of Malianping Village and lateral moraine embankments in these tributaries had the same typical shape features as those of Zhouqu extra-large-scale debris flow deposits.The fans correspond to 1st terraces completely which were formed in the mid-Holocene in Zhouqu area.So these fans were formed by the ancient debris flows.While through comparing radar remote sensing backscattering coefficient with modern debris flows and analyzing the sedimentary deposit sections,the ancient debris flows still exist in the south-east of Zhouqu County.The remote sensing direct identification of debris flows has the important geological significance through comparative analyses of modern and ancient debris flows in different periods and spatial positions that it can not only reveal the development history of the debris flow since Quaternary in Zhouqu area and reflect indirectly the process of climate change at the geological period scale,but also provide data support for susceptibility analysis of the debris flow in the future.