erosion rate of a younger dryas ciroue glacier at krakenes, western

1 981
Annals of Glaciology 2
l ociety
l l a c i o l o g i c aS
o I n t e r n a t i o n aG
DRYASCIROUE
RATEOFA YOUNGER
EROSION
WESTERNNORWAY
AT KRAKENES,
GLACIER
by
E . L a r s e n *a n d J . M a n g e r u d
, orway)
iB
( G e o l o g i sIkn s t i t u tA
t e r g e nA, l l 6 g t .4 1 , N - 5 0 1 4 B e r g e nN
t v d .B , U n i v e r s i t e t e
ABSTRACT
A n e r o s i o n r a t e o f 0 . 5 t o 0 . 6 m ma - r i s
d e d u c e df o r a Y o u n g e rD r y a s c i r q u e 9 1 a c i e r .
T h e e r o s i o n p e r . i o d o f 7 0 0 a w a s d e t e r m i n e df r o m
t h e l a m i n a t e dg l a c i o l a c u s t r i n e s e d i m e n t si n a
s m a l l l a k e i u s t o u t s i d e t h e e n d m o r a i n eo f t h e
c i r o u e a n d r a d i o c a r b o nd a t e s o b t a i n e d b e l o w a n d
a b o v e t h e s e s e d i m e n t s . T h e v o l u m eo f e r o d e d
b e d r o c kw a s c a l c u i a t e d f r o m m e a s u r e m e n tosf t h e
d e p o s i t e d s e d i m e n t s ,o f w h i c h t h e e n d m o r a i n e ,
the glaciofluvial de1ta, and the glaciolacustrine
s e d i m e n t sa r e m o s t i m p o r t a n t . W i t h a c b n s t a n t
erosion rate, the cirque could have formed in
83 to I 25 000 a.
I ON
i NTRODUCT
T h i s p a p e r p r e s e n t st h e c a l c u l a t e d
e r o s i o n r a t e o f a Y o u n g e rD r y a s c i r q u e g l a c i e r
a t K r S k e n e s( F i g . 1 ) , b a s e do n s t r a t i g r a p h i c a l
and glacial geological investigations. The
t w o c r i t i c a l f a c t o r s i n v o l v e d i n s u c ha n
approach are the duration of the erosion
o b n i o d a n d t h e v o l u m eo f e r o d e d b e d r o c k . A
p r e l i m i n a r y r e s u l t , b a s e do n a l e s s a c c u r a t e
e s t i m a t e o f t h e e r o d e dv o l u m e ,i s g i v e n i n
l4an
- g e r u da n d o t h e r s ( I 9 7 9) .
K r S k e n e so n t h e i s l a n d o f V 5 g s d y f a c e s
t h e l , l o r t hS e a . T h e c i r q u e g l a c i e r h e r e b u i ' l t
u o a p r o m i n e n te n d n r o r a i n e , a n d t h e m e l t w a t e r
arainba into a small lake (Fig'2). The level
l o w e r e d s o m ey e a r s
of the lake was artificially
ago, but its former shorelinecan still be
easily traced. The area of the lake was
o r i g- i n a l i y 0 . 0 7 k m z .
S t r a t i g r a p h i c n o m e n c l a t u r ien t h i s p a p e r
i s a c c o r d i n g t o l u l a n g e r uadn d o t h e r s ( . l 9 7 4 ) .
D a t e s a r e g i v e n i n r a d i o c a r b o ny e a r s b e f o r e
p r e s e n t ( . l 9 5 0 ) ,i . e . l + C a B P .
T H ED U R A T I OONF T H EE R O S I OPNE R I O D
In order to date the end moraine, the
l a k e s e d i n t e n t sw e r e c o r e d , a n d t h e g l a c i o l a c u s t r i n e s e d i m e n t st h a t c o u l d b e c o r e l a t e c i
w i t h t h e m o r a i n ef o r m a t i o n w e r e i d e n t i f i e d ( c f .
P e n n i n g t o n1 9 4 7 ) . T h i r t y - n i n e c o r e s w e r e
o b t a i n e d f r o m t h e l a k e . T h e s e s h o w e dt h a t t h e
stratigraphy is very consistent' At the base
(Fiq.3j is a bed of grey, weaklylaminated
i t a y e y - s i 1 t , a b o u t0 ' l m t h i c k . I n o n e c o r e a
b a s l l - t i l l w a s o b s e r v e db e n e a t ht h i s s e d i m e n t '
s u g g e s t i n gt h a t t h e c l a y e y s i l t w a s d e p o s i t e d
ice sheet
i m m e d i a t e l va f t e r t h e S c a n d i n a v i a n
w i t h d r e wf r o m K r 8 k e n e s . A s t h e c l a y e y s i ) t i s
NORTH
SEA
a\
F i g . l . T h e p o s i t i o n o f Y o u n g e rD r y a s e n d
moraines in southern Norvay (key map after
l " l a n g e r u ad n d o t h e r s 1 9 7 9 ) , a n d t h e c i r q u e
m o r i i n e , m e l t - w a t e rc h a n n e l , a n d l a k e ( w i t h
both present level and level before lowering)
a t K r l k e n e s . C o r e ds i t e s i n l a k e ( d o t s ) ,
s e i s m i c p r o f i l e s o n d e l t a ( u n b r o k e nl i n e s ) '
and levelled profiles on endnoraine
( d a s h e da) r e a l s o i n d i c a t e d .
n e i t h e r t h i c k e r ( F i 9 . a ) n o r m o r ec o a r s e - g r a i n e d
n e a r t h e g l a c i a l r i v e r m o u t h ,w e c o n c l u d et h a t
n o g l a c i e i o c c u p i e dt h e c i r q u e i m m e d i a t e l y
a f t 6 r d e g l a c i a t i o n . A b o v et h e c l a y e y s i l t
f o l l o w s b r o w n s i l t y g y t t j a , f r - o mt h e b a s e o f
I q C a B Pw a s
whicha date of 12 320! ]20
agefor
m
inimum
i
s
a
T
h
i
s
(
F
i
g
.
3
)
.
obtained
t h e d e g l a i i a i i o n , a n d w e c o n c l u d e dp r e v i o u s l y
* P r e s e n t a d d r e s s : S t a t o i l , L a g S r d s v n7 8 , N - 4 0 0 0S t a v a n g e r , N o r w a y .
153
Larsen,
Mangerud:
Ev'osion
rate
of a ciz'que
glacder
h e c o u r s eo f t h e g l a c i a l r i v e r i s
F i q . 2 . T h e c i r q u e , e n dm o r a i n e ,a n d l a k e a t K r 8 k e n e s .T
l 4 C - d a t e dc o r e '
i o i t . a i r i g h t ' s i d e ) . A m o wi n d i c a t e st h e s i t e o f t h e
t h a t d e q l a c i a t i o no c c u m e ds h o r t l y b e f o r e t h i s
M i n g e r ua
d n do t h e r s 1 9 7 9 ) . . . .
d a t e (' A
b e do f g r e y g y t t j a s i l t w i t h i n t h e b r o w n
gyttja sequenceis found throughoutthe
silty
'lake-.-ihe-top
of the silty gyttia is dated
l l l O 0J 8 0 I 4 C a B P , t h a t i s , c l o s e t o t h e
endof the Allerdd Chronozone.
A b o v et h e s i l t y g y t t i a f o l l o w s a t h i c k
b e d o f s t r o n g l y I a m i n a t e ds i 1 t , g e n e r a l l yg r e y
i n c o l o u r , b i f w i t h s o m eb r o w n i s hz o n e s ' T h i s
U e a ' i s t t r i c f e r , a n d m u c hm o r ec o a r s eg r a i n e d
near the glacial river mouththan further out
i n t o t h e b a s i n ( F i g . 4 a n dT a b l eI ) , . a n d c a n ,
without doubt, 6e iomelated with the existence
o f t h e c i r q u e - 9 1 a c i e r . T h et i m e i n t e r v a l
o c c u o i e dU v t n e c i r q u e g l a c i a t i o n i1s4 ct h u s
a BP.
u " " . i " i . a L e t w e e nt t i e t i t o o J 8 0
e;il iffi ihe silty svttia and the l0 060 !
]00 and 10 030 I 90 dates from the gyttia overl v i n q t h e l a m i n a t esdi l t ( F i g . 3 ) ; t h a t i s '
qiaciation took place during the YoungerDryas
laCdatings
d h " o n o z o n eT
. h e ' e n t i r es a m p l e sf o r
are, however,taken respectively belowand above
t h e l a m i n a t e ds e q u e n c e .I n o r d e r t o o b t a i n a
moreprecise age'for the lower boundaryof^the
l a m i n i t e ds i l t l t w o a l t e r n a t i v e s e d i m e n t a t i o n
rate curveswere constructed(Fig.S). Both
curves indicate an age of approximately
iO SOOa BP for the iower boundaryof the lamin a t e ds i l t , a n d t h u s t h e o n s e t o f c i r q u e .g l a c i we have
ation. Abovethe laminatedsequence
date (Fig.3) andthe sedio n l v o n er a d i o c a r b o n
meniationrate could therefore not be determined'
ttowever,by assuminga sedimentationrate similar
t o t h a t i u l t b e l o wt h e l a m i n a t e ds i l t ' t h e u p p e r
b o u' 1n0d a r y - otfh e l a m i n a t e ds i l t c a n b e e s t i m a t e d
2 0 0a B P .
to
hlecan thus demonstratethat for this
p a r t i c u l a r s i t e t h e r e w a sn o g l a c i e r - d u r i n gt h e
b d l t i n g , 0 1 d e rD r y a s ,a n dA l ' l e r d d ^. T h e . c i r q u e
q i a c i e i a p p e a r e dh, a d a l i f e t i m e o f , a n d
i i s a p p e a r b i i n s o m e7 0 0 a d u r i n g t h e Y o u n g e r
'154
DryasChronozone.At the sametime the front
o f t n e S c a n d i n a v i ainc e s h e e tw a ss i t u a t e d s o m e
6 0 k mf u r t h e r i n l a n d ( F i g . l ) .
T h ea g e sa n d t h e d u r a t i o no f t h e e r o s i o n a l
p e r i o d a r e g i v e n i n c o n v e n t i o n arla d i o c a r b o n
and others
years. If the suggestionof Oeschger
( t g g O )i s c o r r e c t , t h e 7 0 0 a d u r i n g t h e
YoungerDryaswould corespond to somemore
s i d e i a l ( c i l e n d a r )y e a r s , a n do u r c a l c u l a t e d
e r o s i o nr a t e w o u l db e c o m e s p o n d ' i n gl1eys s .
VOLUME
THESEDIMENT
Our basic considerationis that the total
amountof erosion causedby the cirque glacier
e q u a l st h e t o t a l v o l u m eo f t h e r e s u l t i n g s e d i the modelcan be expressed
ments. Consequently
as (cf. Fig.6):
Vt= Vb+Ve+Vrb* Vd+VL+rp* rdr '
whereTzis the volumeand subscripts refer to
t o t a l d e p o s i t i o nt 1 = t o t a ' l e r o s i o n ) , b a s a l
t i l l b , e n d m o r a i n ee , s e d i m e n t isn r i v e r b e d
r b , d e l t a d , l a k e s e d i m e n t.s{ , , s e d i m e n t ps a s s i n g
t h e l a k e p , a n d d i s s o l v e dm a t e r i a l d s . T h e
r e s u l t s a r e g i v e n i n T a b l e I I , a n dw i l l b e
d i s c u s s e db e l o w .
T h ee n dm o r a i n e( 7 s )
T h ee n d m o r a i n ei s a w e ll - m a r K e ro' l o g e
( F i q . 2 ) w i t h a m a x i m udm
i s t a l h e i g h to f 1 3 m .
A m6ltlwater drainagechannelcuts throughthe
m o r a i n e . B o u l d e r so c c u r r e l a t i v e l y f r e q u e n t l y
on the surface of the eastern part of the
elsewhere.
moraineridge, but are less conmon
G r a i n - s i z ea n a l y s i sf r o m t w o p a r t s o f t h e r i d g e
s h o wa l m o s t i d e n t i c a l d i s t r i b u t i o n c u r v e s
( F i q . 7 ) . l ' { i t h i nt h e m a i nm o r a i n er i d g e , o n t h e
e a s l e r i rs i d e o f t h e c i r q u e , t h e r e i s a s m a l ' l e r
e n dm o r a i n e( F i g . l ) , n n r k i n ga h a l t o r r e a d v a n c e
a cirque gLaciet
Larsen, Marryerwd:Et'osionrate of
morainemayhavebeenderived from rock fa'lls'
i n i f ' e - p . . i . n t c a l c u l a t i o n sw e w i s h e d ' t o i t o i u i . ' t u u g l a c i a l e r o s i o nf r o m t h e t o t a l
i i t o u . - . t o t i o n . M o s to f t h e r o c k - f a l l m a t e r i a l
" i t ' i . u n t p o " i . d t r p " u - a n de n g l a c i a l l y t o t h e
e n dm o r a i h e ,a n d h a s a n a n g u l a r - . f o l m :O, n e
%o t l n e
r o u n d n e sasn a l y s i ss h o w st h a t 9
'in
itJliiot-o.twe-en 20 and 80 nrn size consists
. However
' ansular-rock
;;-;;;;i.;-;aterial
s u b g l a c i a l l ya n d
i"uo*6ntt are also produced
i;ki;; ih.-qiain-size distribution into consid".'eitimate that 5%of the volumeof
itiiiit,
is derived from r99!-f1'l'"
ih.-"na'to.uine
-"- '
( 1 9 7 8 )a l s o
n . f ' . i i ( t g Z s ) a n dA n d e r s o n
subb
e
tween
t
o
'
d
i
s
t
i
n
g
u
i
s
h
u s e da n q u l a r i i ' y
a l r i " v e a - m a t e r i aai n d m a t e r i a l d e r i v e d
.i..iiiit
Their fisures
-tsothare comparable
iffi ;;;"k i;ii'
assumethat all
io-if,. gl obtainedhere'
i u U q l a c i a f f vd e r i v e dm a t e r i a l sw i l I s h o ws o m e
a . o i . . o f r b u n d n e s sb, u t t h i s i s n o t i n a c c o r basal
i.il..-*ifi' observationson Norwegian
tills.
o f t h e t o t a l a n r o u notf i h e g l a c i a l l y
7B.B%
T-25338
Undissolved
l0 030t90
T-2533A
NAOHdissolved
l0 060r r00
Lominoted
sllT,
o
o
8.5
{)
o)
c
o
T - 2532
ll 100t80
T - 2848
ll730ll
o)
=
Uppersilty
gyttio
Gvttiosilt
Lo'wersiltY
gytTlo
C l o y e ys i l t
r - 2534
12320!l
:d
co
l4Cdated core
F i g . 3 . T h e l o w e s t part of the
from the Krdkenes I a k e .
profile thr0ugh
'F 'ir.l.'u.iin-ii
iq.4. Simplified longitudinal
the stratiriir..n.i' compare
velocitiesin
Seismic
3.
rigure
ii:iptv-"iil
glven'
the delta area are
'oBl[,]o-,
M'H'."
f8E
i30lh?iE"PiilftlP'lliH
OUTLET.
AND
INLET
N e a ri n l e t
Nearout'let
Sand
36%
silt
55%
66%
9 %
33%
Clay
d u r i n g i h e d e g l a c ' i a t i o np e r i o d ' S e v e n - p ar onfdi l e s
i g)''1
w e r ei e v e t t e d - a c r o s tsh e ' m o r a i n e ^ ( Fthese^'l,le was calculated frorn
if'L-t6iii vo'lume
a porosity 9f l0%'
haveassumed
ii:rii.r.
N
o
r
w
e g i at inl l s ( e ' g '
f
r
o
m
il;;d';;-".aults
to obtain the
ordei
in
$ii..:iitiEt"tgit),
ng bedrockvol ume'
corresPondi
i o m e ' o i t h e m a t e r i a l i n c l u d e di n t h e e n d
'F 'iiol ;.;5r .o ; A
' i hl t.e r n a t i v e s e d i m e n t a t i orna t e c u r v e s
to".t siltv svttia, gvttia.silt'
a n du i p e r s i l t y g y t t i a ( c f ' F i g ' 3 ) ' . l n e
c o n t i n i . r o u1si n e , r e p r e s e n t i n ga c o n s l a n l
ied'imentationrate, is cirawnwith'in one tiinJiia a.uiation of the three dates.be.low
i h i " o i l i i . i . c u s t r i n e s e d i m e n t i ' T h ed a s h e d
uaseaon the assumptionthat
iin.'ii-tiiniv
'inlreaseamin6rogeniccontent in the
reflecls an in*eased sedimentation
;;iilia
r a t e ; i i w a sc o n s r r u c t e db y a s s u m i nug l i l g l l '
sedimentatlon
r e c i p r o c a l r e l a t i o n s h i p b e t w=e e n
s
r a t e a n dl o s s o f i g n i t i o n : s c / L ' w n e r e
a
n
d
.z
a
c
o
n
s
t
a
n
t
i
q
c
r
i
t
e
,
it-t.iit.niution
h ed a t e s o f I I / 3 u I
ii toss on ignition. T
r4c a BPare accepted
rbo'*J 11 106 I B0
ai-coriect. Betweenthese two dates' Z is
i l i r i v i o n t t a n t ( F ' i s . 3 )' T h u s , t h e . : e g i T : ! tatio'n rate betweenthe two dates ls consld e r e dc o n s t a n t ,a n d t h e c o n t i n u o u sl i n e . c'
i.t*..n'li'.te dates defines the constant'
n-'iiiuilig iu.rage of Z was used for the construction of the curve'
155
Larsen,
Mangerad:
o
#
Etosion
5oom
rate
of a cirque
glacier
mo' s t
i 9 . 6 . A p r o f i l e t h r o u g h - t h ec i r q u e , e n o
m o r a i n e , a n d l a k e a t K r d k e n e s . F o r e x p la n a tion of symbols,see text.
F i g . 7 . G r a . i n - s i zd
ei s t r i b u t i o n f o r t w o t i I I
s a m o l e sf r o m t h e e n d m o r a i n e .
e r o d e d m a t e r i a l s u b s e q u e n t l yd e p o s i t e d i n t h e
v i c i n i t y o f t h e c i r q u e i s c o n t a i n e di n t h e e n d
rnoraine. The end morainehas been carefully
m e a s u r e d ,a n d i s u n l i k e l y t o i n t r o d u c e m o r e t h a n
small errors into the calculations. Themajor
uncertainties are associatedw'ith the recalcul a t i o n s o f t h i s v o l u m e ,d u e t o t h e p o r o s i t y o f
t h e t i l l a n d t h e a m o u n to f r o c k - f a l l d e r i v e d
marerial. tsothestimates of these oarameters
v a l u e s . H e n c eo o s s i b l e e r r o r s i n
are minimum
t h e e s t i m a t e sw i l l f u r t h e r d e c r e a s et h e t i l l
v o l u m ea n d r e s u l t i n a l o w e r e r o s i o n r a t e . A
subjective estimate indicates a maximum
eror
( d e c r e a s e )o f 2 0 % .
The ri ver bed (i/,n)
F i e l d m a p p i n gs h o w st h a t n o m a t e r i a l w a s
d e p o s i t e da l o n g t h e g l a c i a l r i v e r b e d , d u e t o
its steep slope.
The
-Tfiedel ta ( tz6)
voiume of the delta is based on two
seismicrefraction Drofiles and one bore hole
at the intersection of the profiles (Fig.l).
T h e s e i s m i c d a t a s h o w e dt w o l a y e r s a b o v e b e o rock (Fig.4). Thevelocity in the lower layer
c o r r e s p o n d st o s a n d b e l o w g r o u n d - w a t e rl e v e l ,
and is bei ieved to represent the delta. The
bore hole supports the seismic interpretations.
lliehave neither identified a delta of DreY o u n g e rD r y a s a g e n o r t h e c o r r e s p o n d i n gl a c u s t r i n e s e d i m e n t s . T h i s m a y b e b e c a u s et h e
o l d e r s e d i m e n ts e q u e n c ei s v e r y t h i n a n d / o r h a s
156
a s e i s m i cv e l o c i t y s i m i l a r t o t h a t o f t h e d e l t a .
liornrally, the small streamwhich flows from the
c i r q u e o v e r t h e d e l t a a t p r e s e n tc a r r i e s l i t t l e
m a t e n i a l . T a k i n g t h e s e c o n s i d e r a t i o n si n t o
a c c o u n t , t h e t o t a l m e a s u r e dd e l t a v o l u m e h a s
b e e n r e d u c e d6 y 1 0 % . T h e v o l u m eo b t a i n e d f o r
t h e Y o u n g e rD r y a s d e l t a i s c o r r e c t e d f o r p o r e
v o l u m ei n t h e s a m ew a y a s d e s c r i b e d b e l o w f o r
the lake sediments.
T h e l a k e s e d i m e n t s( t z n )
T h e v o l u m eo f g l a c i o l a c u s t r i n e s e d i m e n t s
wascalculatedon the basis of 39 cores (Fig.l).
T h i s v o l u m ei n c l u d e s m i n e r a l s , p o r e w a t e r , a n d
s o m eo r g a n - i cm a t e r i a l . T h e v o l u m ep e r c e n t a g e
o f w a t e r a n d o r g a n i c m a t e r i a l w a s m e a s u r e di n
o n e o f t h e c o r e s . T h e m e a nw a t e r c o n t e n t w a s
6 5 . 2 %a n d t h e m e a nl o s s o n i g n i t i o n w a s 2 . 5 % .
T h e m e a s u r e dv o l u m eo f t h e l a k e s e d . i m e n t w
s as
r e d u c e db y c o r r e s p o n d i n ga m o u n t st o g i v e t h e
e q u i v a l e n t b e d r o c kv o l u m e( T a b 1 eI I ) .
B a s e do n g l a c i a l - r i v e r l o a d m e a s u r e m e n t s
i n f r o n t o f r e c e n t N o r w e g i a ng l a c i e r s , g s t r e m
( 1 9 7 5 ) d e m o n s t r a t e dt h a t b e d - l o a d t r a n s p o r t
u s u a l l y a m o u n t st o 3 0 t o 5 0 %o f t h e t o t a l .
At
K r d k e n e st h e b e d - 1 o a dt r a n s p o r t ( d e l t a ) i s
4 7 , 3 %o f t h e a m o u n to f t o t a l s e d i m e n tt r a n s o o r ted by the glacial river. The sediments
d e p o s i t e d f r o m t h e g l a c i a i r i v e r a m o u n tt o
2 1 . 2 %o f t h e t o t a l a m o u n to f g 1 a c i a 1 1 ye r o d e d
m a t e r i a l . T h e s e s e d i m e n tv o i u m e sa r e m e a s u r e o
accurately. Any errors in thesecalculations
w i I I b e r e l a t i v e l y m i n o ra n dw i l l n o t a f f e c t
t h e f i n a l r e s u lt s .
T h e s e d i m e n t sp a s s i n qt h r o u q h t h e l a k e ( y 6 )
frrSugh
t h e l a k e c a n n o t b e m e a s u r e d . H o w e v e r ,s o m e
d e d u c t i o n s a s t o i t s i m p o r t a n c ec a n b e m a d e .
The laciniate form of the lake indicates that
i t w a s a n e f f e c t i v e s e d i m e n tt r a p , a c o n t e n t i o n
s u p p o r t e db y g r a i n - s i z e a n a l y s i s c o v e r i n g t h e
w h o i e o f t h e g l a c i o l a c u s t r i n e s e q u e n c en e a r t h e
r i v e r i n l e t a n d o u t l e t ( T a b l eI ) . i t i s c l e a r
T A B L EI I . M E A S U R S
EE
DD I M E NVTO L U M EASN D
B IENDGR O CVKO L U M EUSS E DI N T H E
CORRESPOND
D E T E R M I N A TO
I OFNT H EE R O S I OR
NA T E .
Sediment Corresponding
vol ume,
b e d r o c k v o 1u m e ,
m3
m3
B a s a lt i I I
E n dm o r a i n e ,
i n c l u d i n gr o c k f a l l
?
t17000
E n dm o r a i n e ,
excludingrock fall
River bed
94 000
89 000
0
D e lt a
35 000
1 13 0 0
L a k e s e di m e n t s
39 000
12600
S e d i m e n t sp a s s i n g
the lake
N e gi lg i b 1e
D i s s o lv e d s e d iments
N e gil g i b 1e
Total volume
1 1 79 0 0
Total volume,
e x cl u d i n g r o c k f a l I
1 1 29 0 0
R o c kf a l I
5 000
Larsen, Mangerud: ErosLan rate of a cirque gLaciex
"
500m
End mgaotne
F i q . 8 . R e c o n s t r u c t i o no f t h e c i r q u e . g l a c i e r
6 a s e do n t h e e n d m o r a i n ea n d t h e c i r q u e
topograPhY.
that practicaily a1l of the sandin the lake
percenwis dbposited there. The increasing
t a q e o i c l a y t o r v a r d st h e o u t l e t o f t h e l a k e - i s
siioirg inoicaLionthat verv litt1e of
;i;;;
i h " - f i n . t p a i s e d t h r o u g ht h e l a k e ' T h i s . s e d t c o n s i d e r e d n e g li g i b l e '
'i""t' t.irtE-ii-ir'etetoie
Thedissolvedsediments^(765)
is a gnelss' ano
ffidkenes
d
issolved in the
m
a
t
e
r
i
a
l
tne amouit-oi .toO.a
i n . r e f o r e u n i m p o r t a n ta n d n e g l e c t e d i n
..i..'ii
the calculations.
T
he basal till (Yn)
-ffirneii
of the basal t'i ll on the
m
e
a
s u r e da t t w o s i t e s o n l y '
w
a
s
ciroue floor
.ra'in. toirt. of the till wasnot calculated'
io".ul", we wantedto calculate the bedrock
ana tneretore till and other sediments
;;;;;;;,
on the cirque floor before the
.-iiti.o
subV o r n o . . " o i v u i g l a c i e r w a s f o r r n e ds h o u l d b e
i t i * t n . s e d i m e n tv o l u m ed e p o s i t e d b v
i;;;ia
- -t g" Tl ahcei e r
t-h a
c i r q u e a t K r d k e n e si s s i t u a t e d o n t h e
(Fig'
n o r t h e r n - s l o p od t a m o u n t a i n4 3 3 m a ' s ' l '
w
as
a
r
e
a
t
h
e
o
v
e
r
m
o
v
e
m
e
n
t
i
c
e
1). Reqional
i6warJs"tne north-west (Larsenand Longva'
same
,nouUiisheal. Glacier-free slopes in ihe
the
u r [ i - a r i i n s ' t h e Y o u n g e rD r y a s , b u t ,w i t h
s a m ep o s i t i o n a s t h e c i r q u e a t K r a K e n e s ' ,
u s u a l i y h a v e a t i l l c o v e r d e p o s l t e dD y l l e . t h e
i i J n a i i ' u v i u n i c e s h e e t ' T h i i s u g g e s t st h a t
c i r q u e a t K r S k e n e sa l r e a d y c o n t a i n e db a s a l t i l l
*r,.i-if'. cirque glacier appeared' In addition'
w e - s u s p e c rt o c k - i a l l a c t i v i t y t o h a v e c o n t r i U u t e d t o t h e p r e - Y o u n g e rD r y a s s e d i m e n t si n t h e
c i r q u e . T h e v o l u m eo f t h e s e p r e - e x l s l l n g
s e d i ' m e n t si s i m p o s s i b l e t o e s t i m a t e , a n d w e
ir'.".io.. postuiate it to be equal to the volume
The two sedio i - t f r e v o u h g e rD r y a s b a s a l t i l l '
m e n t v o l u m e i a r e t h e r e f o r e e x c l u d e df r o m o u r
Caiculations. This is the major uncertainty in
the calculations.
R A T EO F E R O S I O N
The areas of the cirque and the reconstructed glacier are given in Table III.' and
calculatederosion rates in Table IV' Note
that all the erosion rates are calculated
on the basis of the real areas, and not on map
project i on.
B a s e do n g l a c i a l r i v e r t r a n s p o r t , e r o s l o n
rates over periods of 2 to ll a have been
o. lb9t7a5i n, e d f o r s e v e r a l N o r w e g i a ng l a c i e r s ( 0 s t r e m
K i e l d s e n 1 9 7 9 ) . T h e a v e r a g ee r o s i o n r a t e s
v a r v - f r o m 0 ' 0 7 t o l . O m ma - 1 , w i t h t h e m a j o r i t y
i y i n g b e t w e e n0 . 2 a n d 0 ' 6 m ma - l '
.i'ir.til"i
H o w 6 v e r ,t h e L r o i i o n r a t e s w e r e c a l c u l a t e d
relative to the horizontal projection area of
t h e g l a c i e r s . I f w e c a l c u l a t e i n t h e s a m ew a y '
" u - o 6 t i i n a n e r o s i o n r a t e o f I ' O m ma - 1 ' T h e
b e d r o c ka t K r S k e n e si s a m i c a - r i c h g n e i s s w i t h
w e a t h e r e dz o n e s . T h e b e d r o c k b e n e a t h t h e
glaciers investigated by Kjeldsen and pstrem
c o n s is t s o f c r y s t a l I i n e r o c k s, o f t e n g n e is s e s'
and the resistance to erosion should therefore
b e o f t h e s a m eo r d e r o f m a g n i t u d e . O u r r e s u l t
c o m p a r e sr e m a r k a b l yw e l l w i t h t h e e r o s i o n r a t e s
f o r p r e s e n t N o r v l e g i a ng l a c i e r s .
T h e h e a d - w a l lr e t r e a t i s c a l c u l a t e d
a c c o r d i n gt o o u r e s t i m a t e o f r o c k - f a l l m a t e r i a l .
A s o o i n t e d o u t e a r ' l i e r , t h e r o c k - f a l l v o l u m ei s
value. Nevertheless'
a s s u m e tdo b e a m i n i m u m
t h e q r e a t d i f f e r e n c e b e t w e e nh e a d - w a l l r e t r e a t
( 0 . 1 - m ma - 1 ) s t r o n g l y s u g g e s t st h a t s u b g l a c i a l
erosion was the most important process. Over a
p e r i o d o f 9 a R a p p( ) 9 6 0 ) f o u n d a r e c e n t m e a n
r e t r e a t o f 0 . 0 6 m ma - l f o r a r o c k f a l l i n
northern Sweden. For the head-wall of a
c i r q u e g l a c i e r i n T h o r N i e l s e n R a n g e ,A n t a r c t i c a '
G o l d t h w ; i t ( o r a 1 c o r n r n u n i c a t i o1n9 8 0 ) . e s t i m a t e d
a r e t r e a t o i a p p r o x i n n t e l y 0 . 3 n r na - l . T h e s e
results indicate that our estimate is reasonably
q- o o d .
A n d r e w s( 1 9 7 1, 1 9 7 2 ) , A n d r e w sa n d
L e M a s u r i e r( . l 9 7 3 ) , R e h e i s ( 1 9 7 5 ) , a n d A n d e r s o n
( 1 9 7 8 ) h a v ec a l c u l a t e d e r o s i o n r a t e s f o r c i r q u e
VALUES
O F 1 : 5 O O O ' T H EL A S TT H R E E
I T HP L A N I M E T E R .MOANP SW I T HA S C A L E
M E A S U RW
ED
AREAS
B
TO
T A B L EI I I .
ACCORDIN
GF I G U R E
A
R
E
H
E
A
D
W
A
L
L
A
N
D
R
E
C
O
N
I
T
R
U
b
i
E
6
E
L
N
C
T
T
N
A R EC O R R E C TFEODRS L 6 ' P ;N I i E L T S . T H E
210 000 m'?
cirque
Area of horizontal projection of the ent'ire
170000m'?
glacier
Area of horizontal projection of the reconstructed
320 000 m'?
Real area of the cirque floor andwalls
250 000 m'?
glacier
Real area of the base of the reconstructed
70 000 m'?
g
l
a
c
i
e
r
R e a l a r e a o f t h e h e a d - w a l l a b o v et h e r e c o n s t r u c t e d
AND AREASGIVEN
ER
DO S I ORNA T E S . T H EVOLUMES
TABLE I V . C A L C U L A TE
A N DI I ]
a)
T o t a l c i r q u e e r o s i o n ( 1 1 7 9 0 0 n 3 / 3 2 00 0 0 m ' z 1 7 0 0
Subglaciae
l rosion
H e a d - w a l lr e t r e a t
( 1 1 2 9 0 0 n 3 / 2 5 0 0 0 0 m ' ? 1 7 0a0)
( 5 0 0 0 m 3 / 7 0 0 0 0 m r l 7 0 0a )
T A B L EI I
AE
RS
EF R O M
IN PARENTHES
0 . 5 m ma - l
0 , 6 m ma - l
0 . 1 m ma - ]
157
a cirque glacier
Larsen, Mangerud: Erosion tate of
qlaciers in various parts of the wor1d,and
iornO tftut the erosion rate is low in polar
( B a f f i n I s i a n d ) a n d m u c hh i g h e l i n
oiili"tt
l e m p e r a t e ' g l a c i e r s( R o c k yM o u n t a i n s' ) G e n e r a l l y , o u r r e s u l t s - s u p p o r tt h a t c o n cl u sl o n '
t h e e r o s i o n r a t e a t K r d k e n e sb e i n g b e t w e e nt n a t
r o u n t ani s - g l a . c i - e r' s
o f t s a f f i n I s l a n d a n d R o c k )M
H o w e v e rw
, ith the uncertainties involved ln tne
d i f f e r e n t e s t i m a t e s , a n d t h e l a r g e n u m b e ro f
factors influencing the cirque erosion, a
r i q- o r o u s a n a l y s i s i s n o t p o s s i b l e a t p r e s e n t '
The pre-cirque bedrocksurface is unknown'
B v a s s u m i n bt h i s t o b e a s m o o t h e dc o n t i n u a t i o n
of tilu adiicent slopes, this surface is recons t r u c t e d . - F r o ma p r o f i l e t h r o u g h t h e c e n t r a l
iiii 6i the cirque (Fig.9), it can be deduced
t h a t a d e e p e n i n go f f r o m 5 0 t o 7 5 m o f t h e
s u r f a c e - h a s t a k e n p l a c e o v e r m u c ho f
Uearoct<
the cirque.
q--
--- liom
G-crque bedrock surroce
F i q . 9 . A p r o f i l e t h r o u g ht h e c i r q u e s h o w i n g
6 r e s e n t a n d a s s u m e dp r e - c i r q u e D e o r o c K
surface. No vertical exaggeratl0n'
It is unlikely that the erosion rate was
c o n s t a n td u r i n g t h e w h o l e p e r i o d o f c i r q u e
formation, but-a cirque glacier with a constant
e r o s i o n r a t e o f 0 . 6 m ma - ] w o u l d r e q u l r e - T r o m
m'
e:-to f25 000 a in order to erode 50 to 75
Fr"ih."tot., the cirque glaciation has been
interrupted by ice-sheet glaciatl0n' an0
assume
certainiy alsb ny ice-free periods'- we
i h a t t h e " i c e - s h e e te r o s i o n w a s n o t l a r g e r
"iit'i. in. cirque than on both sides,-and thus
glaciers
ihii il'. ii"que is formedby cirque
d u r i n g t h e M i d d l e a n d U p p e rP l e i s t o c e n e '
AC
- KNOI^iLEDGEMENTS
in
a ; ; d . r e a l . 0 d d v a r L o n g v ap a r t i c i p a t e d
t0
most oi the field work, and also contributed
discussions. cand.mag' Erik Sde,
iirittrf
i ; ; k ; . ; h e l p e dw i t h t h e s e i s m i c i n t e r p r e t a t i o n s '
a;;;:-;.;:
b i u i n a K i r k h u s a n d l u l rH a r r v I s a c h s e n
1 4 Cd a t e s w e r e
uilitt.a"ln the field. All
ii..iea out by Dr Reidar Nydal and siv' ing'
i i l i n i r G u l l i - k s e na i t h e T r o n d h e i mR a d i o l o g i c a l
by
D;ii;; Liboratorv. The figures were drawn
M i s s E l l e n l r g e n s a n d l " 1 rJ a n E ' L i e n ' l n e
wai read criticaltv 9v gr Bidrn G'
;;;;t;tiat
n n l u i t u n ' a n d D r B r i a n R o b i n s ' R o b i n sa l s o .
. . r t L i i " o t h e E n g l i s h l a n g u a g e '. M r s S o i v e i g
H e l l a n dt y p e d t h e m a n u s c r i p t ' F i n a n c r a l s u p p o r r
for
w i s q i v e n " b v t h e N o r w e g i a nR e s e a r c hC o u n c i l
; ; ; . ; ; ; - ; " a " -H u m a n i t i e s ( N A V F a) n d t h e U n i v e r s i t v
To al l these perionsand institutions
;;';;;;";.
we proifer our sincere thanks'
REFERENCES
t- W 1978 Cirqueglacier erosion rates
nnOerson
and characteristics of neoglacial tills'
P a n g n i r t u n gf i o r d a r e a , B a f f i n I s l a n d '
N . t l . T . , C a n a d aA. r c t i c a n d A L P i n e
R e s e a r c h1 0 ( 4 ) : 7 4 9 - 7 6 0
'A n-d r-e w sJ T 1 9 7 1 E s t i m a t e s o f v a r i a t i o n s i n
g l a c i a l e r o s i o n f r o m t h e v o l u m eo f c o r r i e s
a n d m o r a r n e s . G e o l o g i ' a ' S o c t e t Ao ^ f
Ameri'ca. Abstracts uith Ptograms 3(7):
493
l58
A n d r e w sJ T 1 9 7 2 G l a c i e r p o w e r ' m a s sb a l a n c e s '
v e l o c i t i e s , a n d e r o s i o n a l p o t e n t i a l'
e,
Zeits chrif t f'u-r' GeomotphoLogi
13: 1-17
SuncLementband
A n d r e w sJ ' T , L e M a s u r i e rW E 1 9 7 3 R a t e s o f
Q u a t e r n a r yg l a c i a l e r o s i o n a n d c o r r i e
formation, Marie Byrd Land, Antarctica'
G e o t-o\ eq du1)( ? ) : 7 5 - 8 0
1979 MaterialtransportunderKjeldsen0
sdkelseri norske bre-elver 1978' Norges
Vassdrags- og Elektrisitetsoesen'
HydroLogisk
Vassdragsdirektoratet.
3-79
Audeling' RaPPott
L a r s e n E , L o n g v a0 U n p u b l i s h e d . J o r d a r t s k a r t iegging, glasialgeologi og kvarter
s t r a t i q r a f i p 3 S t a d o g V 6 9 s d Y ,Y t r e
N o r d f j 6 r d . ( C a n d .r e a l ' t h e s i s '
U n i v e r s i t Y o f B e r g e n' 1 9 7 9 )
M a n- g e r u dJ , A n d e r s e nS T , B e r g i u n d B E . ' D o n n e r
J J 1 9 7 4 Q u a t e r n a r ys t r a t i g r a p h y o f
Norden,a proposal for terminology ald
c l a s s i f i c a t i o n . B o r e a s3 ( 3 ) : 1 0 9 - 1 2 7
M a n- q e r u dJ , L a r s e n E , L o n g v a0 , S d n s t e g a a r dE
1979 Glacial history of western Noruay
1 5 , 0 0 0 - 1 0 , 0 0B0. P . a c r era+ sC8 ( ? ) : 1 7 9 - 1 8 7
and other
O e s c h g e rH a n d 6 o t h e r s 1 9 8 0
p a r a m e t e r sd u r i n g t h e Y o u n g e rD r y a s c o l d
phase. Radiocarbon 22: 299-310
g s t r e m G 1 9 7 5 S e d i m e n tt r a n s p o r t i n - g l . a c i a 1
m e l t w a t e rs t r e a m s . I n J o p l i n g A V a n d
McDonaldB C (eds) GLaciofluuial and
gLaciolacustrine sedimentation' Tulsa, 0K'
c aleontologists.and
5ociety of EconomiP
M ' i n e r a i o g i s t s1:0 1 - 1 2 2( S p e c i a l P u b li c a t i o n
23)
P e n n i n g t o nW 1 9 4 7 L a k e s e d i m e n t s : p o 1 1 e nd i a north
lram from the bottomdeposits of-the
6 a s i n o f W i n d e r m e r ien n o r t h e r n E n g l a n d '
PhilosophicaL Transact'i'ons of the .Rogal
s o c i e t y o f L o n d o n2 3 3 ( 5 9 6 ) : 1 3 7 - 1 7 5
t f mountain
R a o oA 1 9 6 0 - R L c e n td e v e l o p m e n o
s l o p e s i n K l i r k e v a g gaen d s u r r o u n d i n g' s
norihern Scandinavia. Geografiska
A n -nJa' L- iegrz4' s? '( 2 - 3 ) : 6 5 - 2 0 0
source, transportationand
Reheis-'l'i
d e p o s i t i o n o f d e b r i s o n A r a p a h oG l a c i e r '
F r o n t R a n g e ,C o l o r a d o , U ' S ' A ' J o u r m a l
o f c t a c i o l o s U 1 4 ( 7 2 ) :. 4 0 7 - 4 2 0
s e l m e r - b l s e n R 1 - 9 i 7r n g e n L / r g e o l o g i ' d e l l s e
j o x d l a g . D e L 2 . T r o n d h e i m ,T a P i r