Scales and rates of glacial sediment removal : a 20 km long , 300 m deep trench created beneath Breioamerkurjokull during the Little Ice Age

A 20 km long, 25 km wide trench , w hi ch e:-;tends to 300 m be lO\\' sea le\'e l, is beli eved to ha \'e bee n crea ted b\' remO\'a l o f sed iment during th e ad"<ln ce of Breioa m erkLllj bkul1 in th e Little l,ce Ag~i Bet\\'ee n 1732 a nd 1890 , th e g l ~c i e r ach-a nced by 9 km, co\'ered a n a rea of 4S km a nd exca , 'a ted a \'01 u m e of S x 10' m :l, eq ui\ 'alent to a n C\ \ 'erage o f 110 m Sl \ 'er this a rea , Ave rage sedim ent-remond ra te during th e 158 yea rs \I"as 32 x 10() m .l a I or 0 ,7 m a I km 2 a \'e raged O\'e r the a r ea co\'e red b y th e ach-a ncin g' g"lacie r. C a lcula ted OHT th e \\'ho le c1ra in aQ:e a rea o f th e • ' : ....... ' ) • LJ ,) I eas ts rn bran ch o f th e g laC ier o r 750 km -, th e d enuda tIOn ra te \I'o uld JJe t xI I 0 m a km , Flu\'la l processes a re es tima ted to ha\'e ea rn ed a bout 30 x 10 m a ,and th e sedim ent Ou :-;es w ithin th e ice a nd by th e d efo rmin g subglac ia l till a re es tim a ted to be I 0') I 106 :J I 'I T I I ~ , , I I ' 1 ' a nc m a , resp ec tl "e y, le aye rage sec Iment co ncentra tI On In t l e g aCla stream s \\'o uld ha \ 'C bee n a bo ut 10 kg III 3 Such co ncentra tio ns ha \ 'C bee n measured in Ice la ndi c ri\ 'C rs durin g j o kulhl a ups a nd surges, Se\'C ra l surging n 'ents look place during th e adva nce or Breida m erkurj(ikull , a nd j okulhl a ups dra in reg ul a rl y benea th th e g lacie r from ice-d a mmed m a rgin a ll9kes , Th e prese nt ra te o f tra nspo rL, a lthough co nsid era ble, seem s to be a bo ut 10 x lOb m a I, or whi ch 30% is tra nspo rred by th e ri\ 'C r to th e sea a nd 70 % is dumped into a proglac ia l la ke ,