Glacier Lake Outburst Floods (GLOFs)—Mapping the Hazard of a Threat to High Asia and Beyond - Impact of Global Changes on Mountains: Responses and Adaptation - page 325

Hence, classically such a Glacier Lake Outburst Flood (GLOF ) occurs
when water dammed by a glacier or a moraine is released. A water body
that is dammed by the front of a glacier is called a marginal or proglacial
lake, a water body that is on glacier ice is called supra-glacial lakes, and
a water body capped by the glacier is called a subglacial or englacial
lake (Ives 1986, Buchroithner 1996). Supra-glacial lakes often appear to
merge with moraine-dammed lakes, or may develop contemporaneously
as composite forms. When a marginal lake bursts, it may also be called a
marginal lake drainage. When a sub-glacial lake bursts, it may be called
a jökulhlaup.
Thus, a jökulhlaup describes a sub-glacial outburst fl ood. It is an
Icelandic term that has been adopted into the English language, originally
only referring to glacial outburst fl oods from Vatnajökul, which are triggered
by volcanic eruptions, but later it has been accepted to describe any abrupt
and large release of sub-glacial water (Ives 1986). Initially, this term has,
however, frequently erroneously been used for GLOFs in general (cf.
Buchroithner 1996).
Glacial lake volumes vary signifi cantly, but may hold millions to
hundreds of millions of cubic metres of water (cf. Buchroithner 1985,
Cenderelli and Wohl 2001). Catastrophic failure of the containing ice
or glacial sediment contained in the 'dam' can release this water over
periods of minutes to days. Peak fl ows between 2000 m³ up to 30.000 m³
per second have been calculated for such events (Cenderelli and Wohl
2001, Richardson and Reynolds 2000) suggesting that a v-shaped canyon
of a normally small mountain stream could suddenly develop into an
extremely turbulent and fast-moving torrent some 50 metres high (cf.
chock block in gorge near Pangpoche after the 1977 Nare Drangka GLOF;
Buchroithner et al. 1982).
There are a number of imminent deadly GLOFs situations that
have been identifi ed worldwide. Imja Tsho located in the Everest region
(Watenabe et al. 2009) and Tsho Rolpa glacier lakes gained international
fame. The latter one is located in the Rolwaling Valley, about 110 kilometres
northeast of Kathmandu, at an altitude of 4,580 m. It is dammed by a
150 m high unconsolidated terminal-moraine dam. The lake is growing
larger every year due to the melting and retreat of the Trakarding Glacier
(cf. Fig. 14.1), and has become the largest and one of the most dangerous
glacier lake in Nepal, with approximately 90 to 100 million m³ of water
stored (ICIMOD 2011; http://www.dhm.gov.np/tsorol/background.htm;
accessed December 2012). Remarkable mitigation measures, supported by
the international community, have in this instance been materialized.