We describe and interpret a catastrophic subsidence in the Dalk Glacier, East Antarctica, occurred in the morning of 30 January 2017. We analysed a dataset of high-resolution aerial photographs and video records captured ten days before, one hour after, and ten days after the event by unmanned aerial systems (UASs) as well as UAS-derived digital elevation models (DEMs). We reconstructed a subsidence mechanism as follows: An englacial cavern measuring about 885,000 m(3) with a thin roof existed before the event. There was a channel of the surface and near-subsurface meltwater flow from the Boulder Lake to the Prydz Bay passing nearby the cavern. About a day before the event, an intensive meltwater flow began from the Boulder Lake. The meltwater accumulated on the cavern rooftop leading to its initial collapse. In several days, the meltwater completed the process of subsidence and collapse of the cavern. The event led to the formation of an ice depression about 40,000 m(2) in size and up to 43 m deep. Our results demonstrate that ice-surface hydrological processes can cause rapid, deep subsidences of large areas in glaciers, without involving englacial water outbursts from subglacial lakes as well as subglacial geothermal or volcanic activity.