Corresponding to an emergency request from Sentinel Asia related to a glacial lake outburst flood (GLOF) reported in Bhutan on Jun. 28, 2015, the Japan Aerospace Exploration Agency (JAXA) performed an emergency observation at 5:59 (GMT) on Jul. 2, 2015 by means of the Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) aboard the Advanced Land Observing Satellite-2 (ALOS-2, "DAICHI-2").
According to an ALOS dataset, "the Glacial Lake Inventory of Bhutan using ALOS ("DAICHI") Data", two glacier lakes with GLOF potential as Lake A and B are located in [89°34'50.0"E; 28°4'7.7"N] and [89°36'7.7"E; 28°6'54.1"N] in a headwater of the Mo Chu river basin, western Bhutan.
Lake outline was delineated manually for Lake A (Fig. 2a) and B (Fig. 3a). In a PALSAR-2 image, lakes are shown as homogeneously dark areas, because low backscatters return from the water surface, which enables manual delineation of lake outlines from an amplitude image. Lake outlines before the GLOF were also delineated from past images of PALSAR-2 (Apr. 23, 2015) (Figs. 2b; 3b), Landsat 8 (Mar. 8, 2015) (Figs. 2c; 3c), and ALOS PRISM/AVNIR-2 (Dec. 22, 2010) (Figs. 2d; 3d).
The outline differences of Lake A denotes a remarkable expansion (+48.0%) from Mar. 8 to Apr. 23 followed by a remarkable shrinkage (−52.9%) from Apr. 23 to Jul. 2 (Fig. 4). On the other hand, no remarkable area change is recognized (< 20.0%) in Lake B in the same period.
From this result, Lake A has a higher potential as the source of the GLOF. It is located at a glacier terminus surrounded by a moraine (Fig. 5). Comparison of Figs. 2a and 2b denotes different backscatters in a part of the moraine, which suggests that the moraine was collapsed by the GLOF. More detail investigations including field surveys are necessary to reveal and understand this event scientifically.
These obtained results have been contributed to a governmental organization of Bhutan. JAXA would carry out rapid observations against such a mountain hazard in remote regions in cooperation with concerned authorities. Related results would be distributed to relevant organizations and this website.
JAXA has been providing "Glacial Lake Inventory of Bhutan using ALOS (Daichi) Data" which contains glacial lake outlines and related geographical information for the glacial lakes in the Bhutan Himalaya. This project was supported by JICA and JST under SATREPS from 2008 to 2012.
Digitized outlines of Lake A and B (zipped KML files; 30 KB) are able to be downloaded from » here.
© JAXA EORC