There is a spectacular video of how fast a thermite reaction can melt
through blocks of ice at www.mythbusters-thermite.notlong.com

Two clips showing the burning of different mixes of thermite and several
views of the melting process - it's quick!

--
Rodney Blackall (retired meteorologist)(BSc, FRMetS)
Buckingham, ENGLAND
Using Acorn SA-RPC, OS 4.02 with ANT INS and Pluto 3.03j