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Glacial Lake Outburst Flood (GLOF) is an inherent threat in countries in the Hindu Kush Himalayan (HKH) region and is projected to increase in the face of climate change. One of the recent GLOF events in the region was the outburst of Lemthang Tsho (lake) in Bhutan on 28 July 2015. This paper discusses the cause and impact of the event based on the analysis of multi-temporal satellite images and field observation. The event, which was small to medium in volume, was triggered by the emptying of two supraglacial ponds located upstream of Lemthang Tsho. The area had experienced heavy rainfall till the morning of 28 July. On the same day, at 7:10 am local Bhutan time, a 5.1 magnitude earthquake struck about 177 km southeast of the lake. In the absence of firsthand information from the field, it cannot be confirmed that these two events triggered the lake outburst that took place around 3 pm. However, the possibility cannot be ruled out, either. The rainfall and earthquake are likely to have had a role in triggering the outburst.