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Ice-Dusting Experiments to Increase the Rate of Melting of Ice
Williams, G. P.
uuuill[ufiu|iuuuuliillil
NATIONAL RESEARCH COUNCIL CANADA
DIVISION Or. BUILDING RESEARCH
ICE.DUSTING EXPERIMENTS TO INCREASE THE RATE O3' MELTING OF ICE
by G. P. Williams
, q l . , l A L Y Z E D
T e c h n i c a l P a p e r No. 239 of the D i v i s i o n of Building Research OTTAWA January 196'lTABLE OF CONTENTS
1952 Dusting E>cperiments at Ottawa
1963 Dusting E>rperiments
1964 Ice-dusting Experiments at Inuvik
1 965 Ice -dusting E>cperiments
General Conclusions Acknowledgernents R e f e r e n c e s 5 7 l l
r 8
z 0
2 LICE-DUSTING EXPERIMENTS TO INCREASE T H E R A T E O F M E L T I N G O F I C E
by
G . P . W i l l i a m s
I n 1 9 6 1 , i n r e s p o n s e t o a r e q u e s t f r o m o r g a n i z a t i o n s i n t e r e s t e d in extending the navigation season, the Snow and I c e Section of the Division of Building Research undertook a s t u d y o f t h e u s e of dust to accelerate the melting of ice
c o v e r s i n various parts of Canada. I n the first part of
t h e study an evaluation of ice dusting was made based on
p u b l i s h e d information. T h e factors that affect the melting
o f i c e a n d t h e r e q u i r e m e n t s o f i c e - d u s t i n g m a t e r i a l s w e r e
i n v e s t i g a t e d ( I ) . I t was concluded that under some conditions
d u s t i n g would accelerate the melting of ice, but that field t r i a l s w e r e r e q u i r e d t o e s t a b l i s h i t s e f f e c t i v e n e s s .
S m a l l - s c a l e d u s t i n g trials were undertaken at Ottawa
i n t h e s p r i n g - m e l t p e r i o d s o f . L 9 6 2 a n d 1 9 6 3 . I n 1 9 6 4 , m o r e
e x t e n s i v e t r i a l s w e r e c o n d u c t e d a t I n u v i k , N . W . T . I n 1 9 5 5 ,
t r i a l s w e r e c o n t i n u e d a t I n u v i k a n d s m a l l - s c a l e t e s t s w e r e
undertaken at Ottawa and at Milne Inlet, Baffin Island.
T h i s p a p e r r e p o r t s t h e r e s u l t s a n d c o n c l u s i o n s f r o m t h e s e f i e l d e x p e r i r n e n t s a n d , b a s e d o n t h e s e s t u d i e s , p r e s e n t s
t h e limitations o f various ice-dusting techniques.
T h e o b j e c t i v e in applying a thin layer of suitable dust i s to reduce the amount of short-wave radiation that is
r e f l e c t e d f r o m t h e s u r f a c e , a n d t h u s i n c r e a s e t h e h e a t a b s o r b e d . T h e percentage of the total incoming short-wave radiation
t h a t i s r e f l e c t e d i s t e r m e d t h e t r a l b e d o r t . F o r n e w s n o w , t h e a l b e d o m a y b e a s h i g h a s B 0 t o 9 0 p e r c e n t . F o r m e l t i n g
s n o w a n d i c e , i t v a r i e s f r o m 4 0 t o 6 0 p e r c e n t . T h e a l b e d o o f a n i c e c o v e r d a r k e n e d b y a s u i t a b l e d u s t r a n g e s f r o m I 0
t o 2 0 p e r c e n t . T h e i n c r e a s e i n s o l a r r a d i a t i o n a b s o r b e d
b e c a u s e of dusting wiII depend on how much the albedo of t h e n a t u r a l s u r f a c e c a n b e r e d u c e d b y d u s t i n g .
T h e amount of incorning short-wave radiation available a t t h e site during favourable dusting periods limits the amount
o f additional ice that can be melted. T h e estimated short-wave
- z
w h e n t h e a v e r a g e a i r t e m p e r a t u r e i s 3 2 " F , a s c a l c u l a t e d b y M a t e e r ( Z ) , i s s h o w n i n F i g u r e l . W i t h i n a r e g i o n , s h o r t - w a v e r a d i a t i o n w i l l v a r y f r o m s e a s o n t o s e a s o n a n d f r o m l o c a t i o n t o l o c a t i o n . I n the south of Canada the average short-wave radiant h e a t available during the early part of the melting period (March)
r a n g e s f r o m 3 0 0 t o 3 5 0 c a L / s q c r n / 2 4 l n r ( 1 1 0 0 t o I 3 0 0 B t u / s q f t / Z 4 i n r ) . I n the Far North, d u r i n g the melting period in June, the heat
a v a i l a b l e f r o r n s o l a r r a d i a t i o n r a n g e s f r o m 5 0 0 t o 7 0 0 c a L / s q e t n / Z + t t r ( Z Z O O to 2 6 0 0 B t u / s q f t / 2 4 t u | . A s s u m i n g t h a t t h e a l b e d o o f a
n a t u r a l i c e c o v e r c a n b e r e d u c e d f r o m 5 0 t o 2 0 p e r c e n t b y d u s t i n g , t h e i n c r e a s e in heat available for melting under favourable conditions i n southern Canada would be 105 caI/sq
" t n / Z + h r and in the F a r N o r t h Z I 0 c a l / s q " t n / Z + t r . T h i s c o r r e s p o n d s t o a n i n c r e a s e i n t h e m e l t i n g r a t e o f a b o u t ] t o t . 0 i n . ( 1 . 5 t o 2 . 5 c m ) o f i c e p e r d a y . S e v e r a l d i f f e r e n t d u s t s w e r e a p p l i e d t o s n o w a n d i c e c o v e r s u n d e r a variety of weather conditions. I n g e n e r a l , the effectiveness o f t h e d u s t s i n i n c r e a s i n g t h e r a t e o f m e l t i n g w a s a s s e s s e d b y
c o m p a r i n g the rnelt rate of dusted ice or snow with that of adjacent u n d i s t u r b e d s n o w o r i c e . T h e s e r e s u l t s w e r e o f t e n q u a l i t a t i v e , a s f l o o d i n g p r o d u c e d by natural melting of snow and ice late in t h e m e l t s e a s o n m a d e a c c u r a t e m e a s u r e m e n t o f m e l t i n g r a t e s
d i f f i c u l t . W h e n e v e r p o s s i b l e the albedo of test and natural s u r f a c e s was r n e a s u r e d w i t h a p o r t a b l e K i p p s h o r t - w a v e r a d i o m e t e r . T h e s e m e a s u r e m e n t s w e r e u s e f u l i n c o m p a r i n g t h e e f f e c t i v e n e s s o f d i f f e r e n t d u s t i n g t e c h n i q u e s . S o m e o f t h e s e t e c h n i q u e s , s u c h a s s i m p l y r e m o v i n g t h e s n o w c o v e r t o e > < p o s e t h e u n d e r l y i n g i c e a n d t h u s d e c r e a s e t h e a l b e d o , a r e n o t s t r i c t l y d u s t i n g t e c h n i q u e s . T h e y h a v e b e e n i n c l u d e d i n t h i s p a p e r , h o w e v e r , a s t h e y w e r e a p a r t o f t h e s e f i e l d e > c p e r i m e n t s , 1 9 5 2 D U S T I N G E X P E R I M E N T S A T O T T A W A
S e v e r a l different dusts \f,rere applied to snow and ice c o v e r t e s t s i t e s i n t h e O t t a w a a r e a d u r i n g t h e s p r i n g - r n e l t p e r i o d o f . L 9 6 2 . T a b l e I i s a s u r n r n a r y o f t h e a r e a s c o v e r e d , t h e t l n p e o f dust applied and the application rates. T h e w e a t h e r c o n d i t i o n s t h a t o c c u r r e d d u r i n g t h e t r i a l s a r e s h o w n i n F i g u r e 2 .
D u s t i n g T e s t s o n S n o w C o v e r
F i n e - p e l l e t c a r b o n black was applied on 7 March at the r a t e of about 0. 04 and 0. 08 lb/sq ft (ZOO to 400 g/"q r") on the s n o w s u r f a c e o f t w o t e s t p l o t s , e a c h 1 0 0 s q f t ( 9 s q m ) i n a n r e a . W i t h i n an hour of application the carbon pellets, absorbing heat f r o r n t h e s u n , h a d m e l t e d t h e i r w a y Z t o 3 i n . ( 5 t o 2 . 5 c m ) i n t o the snow pack.
- 3
W h e n the dust was first applied, the albedo of the dusted s u r f a c e w a s b e l o w l 5 p e r c e n t , c o m p a r e d w i t h a n a l b e d o o f 5 0 t o
6 0 p e r c e n t for the natural snow cover. A f t e r t h e p e l l e t s h a d
p e n e t r a t e d i n t o t h e s n o w c o v e r , t h e s u r f a c e b e c a m e r r g r e y - l i k e r t i n c o l o u r with an albedo of 15 to 20 per cent.
T h e e x c e s s m e l t - w a t e r p r o d u c e d a t t h e d u s t e d s u r f a c e d r a i n e d into the snow cover and collected on the first hard layer
o f snow, A t n i g h t t h i s f r o z e , and produced an ice layer which
g r a d u a l l y enlarged as melting continued. F i g u r e 3 , showing
r e p r e s e n t a t i v e s n o w p r o f i l e s o f the natural and dusted siteso
i l l u s t r a t e s t h e g r o w t h o f this ice layer after 2 ar'd 6 days.
A l t h o u g h there was a marked decrease in the depth of the snow a t t h e dusted site, the total water equivalent of the snow cover d i d n o t decrease appreciably when compared with the undusted
a r e a . B e c a u s e t h e s n o w c o v e r w a s l a y e r e d a n d c o n t a i n e d i c e
l e n s e s of varying thickness, h o w e v e r , t h e t o t a L w a t e r e q u i v a l e n t
c o u l d n o t b e m e a s u r e d a c c u r a t e l y .
O n 1 2 M a r c h a s n o w f a l l o f I 0 t o 1 2 i n " ( 2 5 t o 3 0 c m )
o c c u r r e d . T h e albedo of both the dusted and control snow
s u r f a c e s i n c r e a s e d t o o v e r 6 0 p e r c e n t . W i t h t h e w e a t h e r
c o n d i t i o n s that prevailed, i t w a s 6 to 7 days after the new
s n o w f a l l before the albedo of the dusted site was again lower
t h a n the undusted site. D u r i n g the last few days of the melt
p e r i o d t h e s n o w c o v e r a t t h e t w o d u s t e d p l o t s m e l t e d m o r e
r a p i d l y than the adjoining cover. T h e d u s t e d c o v e r melted
c o m p l e t e l y by ?Z Marcn., about 3 days earlier than the adjacent u n d i s t u r b e d s n o w c o v e r .
D u s t i n g T e s t s o n I c e C o v e r
F i g u r e 4 illustrates t h e sequence of ice melting on
t h e d u s t e d i c e c o v e r s . I n t h e f i r s t s t a g e , a n i n c r e a s e d r a t e
o f melting was quite evident at all test sites, and after 5 to
6 d a y s the depth of melt-water a t t h e t e s t s i t e s v a r i e d f r o m
a rnaximurn of 8 in. (20 cm) (test area No. 1) to a minirnurn o f 4 i n . ( 1 0 c m ) a t t h e t e s t a r e a w i t h j u s t t h e s n o w r e m o v e d . T h e i c e surface under the water was quite honeycombed,
w i t h t h e d u s t p a r t i c l e s e m b e d d e d i n t h i s s u r f a c e . T e s t a r e a
N o . 4 (with just the snow removed) a n d t e s t a r e a N o . 6
( c a r b o n b l a c k ) d i d n o t d e v e l o p t h i s h o n e y c o m b e d s u r f a c e . I n t h e s e t w o c a s e s t h e w a t e r - i c e i n t e r f a c e w a s s r n o o t h . A f t e r about 12 days of melt, the water depth of aII test sites
r e a c h e d B in. (20 cm) and remained at approximately t h a t
- 4
I n the early stages of melting the albedo of the dusted t e s t p l o t s r a n g e d f r o m I 0 t o 2 0 p e r c e n t c o m p a r e d w i t h a n a l b e d o o f 50 to 55 per cent for the natural ice cover. A s the n a t u r a l i c e c o v e r c o n t i n u e d t o m e l t i t s a l b e d o d e c r e a s e d t o 2 0 t o 30 per cent" E a r l y in April the albedo of both the dusted a n d n a t u r a l surfaces increased to about 40 per cent because of n e w snowfall" O n 7 April spring rain resulted in a
water-c o v e r e d i water-c e s u r f a water-c e w i t h a n e s t i m a t e d a l b e d o o f 1 0 t o 1 5 p e r water-c e n t . I t was estimated that both the dusted and natural surfaces
r e t a i n e d this 1ow albedo for the remainder o f t h e melt period. A f t e r the water depth had reached 8 in. the rate of m e l t i n g o f t h e i c e c o v e r at the dusted sites equalled that of t h e n a t u r a l ice cover. T h e test sites that had a slower rnelting r a t e to begin with (test site No. 4 with just the snow removed) t r c a u g h t upt! with the test sites which at first had a faster rate o f melting. A l t h o u g h the increased rate of melting was limited t o the early stages of meltr the ice cover at all the test plots c o m p l e t e l y melted by 6 April, a b o u t l 0 days before the sur-r o u n d i n g ice"
D i s c u s s i o n o f 1 9 6 2 d u s t i n g t e s t s
T J a e 1962 ice-dusting e x p e r i m e n t s i n d i c a t e d that the t y p e of material, s i z e o f particle, a n d r a t e o f application w e r e not very critical, a n d t h a t almost any dark material, u n d e r favourable weather conditions, c o u l d initiate melting. O n c e a layer of water had formed on the ice surface the m e l t i n g p r o c e s s a p p e a r e d t o b e t h e s a m e f o r a l l s i t e s , t h e r a d i a t i o n characteristics o f the surface being deterrnined b y the water. I n c o m i n g short-wave radiation absorbed at t h e w a t e r surface raised the temperature o f the water and i n c r e a s e d the rate of melting of the underlying ice by c o n v e c t i o n . A c e r t a i n percentage of the short-wave r a d i a t i o n would penetrate the water and be absorbed by t h e dusted ice surface under the water.
T h e 1962 experiments also indicated that the ease w i t h which the excess melt water produced by dusting can b e d r a i n e d f r o m a s i t e i s o f i m p o r t a n c e i n a s s e s s i n g t h e p o t e n t i a l value of dusting. I f i t had been possible to drain
o f f the melt water that accumulated at the dusted snow cover ( f o r example, if the snow cover was on sloping pavernent) t h e s n o w c o v e r w o u l d h a v e m e l t e d s o o n e r . T h e d u s t e d i c e c o v e r s w o u l d h a v e m e l t e d m o r e r a p i d l y i f i t h a d b e e n p o s s i b l e t o drain the rnelt holes so that the dusted surface was
- 5
DUSTING EXPERIMENTS
I n 1 9 6 3 l a r g e r s c a l e t r i a l s w e r e c o n d u c t e d . T h e p u r p o s e o f these additional e>cperiments was to:
( a ) investigate whether sirnply rernoving the snow cover was a s e f f e c t i v e a s d u s t i n g ;
(b) find out if applying the dust on top of the snow was a s e f f e c t i v e a s a p p l y i n g t h e dust on the ice surface w i t h t h e s n o w r e r n o v e d , and
( . ) d e t e r m i n e s o m e o f t h e p r o b l e m s a s s o c i a t e d w i t h d u s t i n g a l a r g e r a t e a .
T h e t r i a l s w e r e c o n d u c t e d d u r i n g t h e s p r i n g o f I 9 6 3 i n c o - o p e r a t i o n w i t h M a r i n e S e r v i c e s , D e p a r t m e n t o f T r a n s p o r t , o n a section of the Rideau Canal at Burrittrs R a p i d s , a b o u t 3 0 m i l e s s o u t h o f O t t a w a . T h r e e t e s t s i t e s w e r e e s t a b l i s h e d , e a c h 1 0 0 b y 1 0 0 f t ( 3 0 x 3 0 r n . ) . O n e s i t e w a s d u s t e d a f t e r t h e snow was rernoved frorn it; another had the snow removed f r o r n i t b u t n o dust was applied; and at the third site the dust w a s applied directly to the surface of the snow. T h e material u s e d w a s a f i n e - g r a i n w a s h e d s a n d a v a i l a b l e l o c a l l y , a n d w a s a p p l i e d b y s h o v e l a t a n e s t i m a t e d density of 8 lb / tOO sq ft ( 4 0 k i l o g r n /tO sq m. ). When the dust was first applied on 5 M a r c h t h e f o l l o w i n g a l b e d o s w e r e m e a s u r e d : n a t u r a l s n o w c o v e r , 7 2 p e t c e n t ; s n o w r e r n o v e d a n d e x p o s e d i c e s a n d e d , l 5 p e r c e n t ; s n o w r e m o v e d b u t n o d u s t a p p l i e d t o t h e i c e s u r f a c e , 4 5 t o 6 0 p e r c e n t .
F i g u r e 5 g i v e s d a i l y a v e r a g e a i r t e m p e r a t u r e s , p r e c i p i t a t i o n , a n d short-wave radiation for Marc}n 1963 a t O t t a w a . T h e s e w e a t h e r r e c o r d s , t a k e n a b o u t 3 0 m i l e s n o r t h o f t h e d u s t i n g s i t e , a r e c o n s i d e r e d t o b e r e a s o n a b l y r e p r e s e n t a t i v e o f w e a t h e r c o n d i t i o n s t h a t p r e v a i l e d d u r i n g t h e t r i a l s .
U n f a v o u r a b l e w e a t h e r conditions for dusting prevailed t h r o u g h o u t March. O n 6 March, the day after dusting,
2 j i n c h e s o f h e a v y , w e t s n o w f e l l . E x c e p t for 3 days, 8, L3, a r ' d Zl March, t h e daily air ternperature r e m a i n e d w e l l b e l o w 3 0 ' I ' u n t i l 24 Marc]:,.
- 6
D u r i n g t h i s p e r i o d t h e t e s t s i t e s w e r e c o v e r e d s e v e r a l t i r n e s by varying amounts of new snow. The snow cover was r e m o v e d f r o m t h e t e s t s i t e s o n l 5 M a r c h b u t b e c a u s e o f d i f f i c u l t i e s i n getting the necessary equipment on to the ice t h e 2 in. (5 crn) of snow that felI on 20 March was not removed. T h i s new snow cover did not melt fromthe test plots until 2 4 Marc}n, and even then portions of the dusted areas remained p a r t i a l l y c o v e r e d . F o r a s h o r t p e r i o d ( 2 4 t o 2 7 M a r d n ) t h e i c e a t b o t h d u s t e d p l o t s m e l t e d a t a n i n c r e a s e d r a t e . T h e t e s t p l o t w i t h j u s t the snow removed however melted at about the sarne r a t e a s the undisturbed ice cover. R e m o v i n g the snow cover w a s not very beneficial at this site because the underlying ice w a s white, with a relatively h i g h a l b e d o ( 5 5 p e r c e n t ) .
R a p i d melting of all plots and the natural cover occurred f r o m 2 9 M a r c h t o 2 A p r i l . T h e i c e c o v e r a t t h e s i t e w a s f l o o d e d b y water draining from nearby fields" B y 4 A p r i l there was o p e n water along the edge of the canal and the ice cover at all s i t e s w a s either water -covered or in an advanced stage of rnelting.
D i s c u s s i o n o f 1 9 6 3 I c e - d u s t i n g T e s t s
A l t h o u g h 1963 was an example of a trpoortt year for a d v a n c i n g the melting of ice by dustingr much useful information w a s o b t a i n e d , particularly f r o m an operational point of view.
I n an area where there is frequent snowfall during the m e l t p e r i o d , i t will be difficult to keep the dusted surface free o f snow. E v e n an inch or less of snow can effectively cover t h e dusted surface and reduce the amount of solar radiation a b s o r b e d . ( F o r e x a m p l e , o n 5 M a r c h r e m o v a l o f * in. of snow f r o m t h e w h i t e i c e d e c r e a s e d t h e a l b e d o f r o m 6 3 . 5 t o 4 6 p e r c e n t . ) I t was also noted that small amounts of new snow can drift onto t h e dusted area and effectively cover the surface.
A n o t h e r problem is to know when first to apply the dust. I f i t i s s t a r t e d t o o e a r l y m u c h n e e d l e s s s n o w c l e a r i n g o r r e -d u s t i n g will be require-d" I f the operation is started too late, f a v o u r a b l e weather conditions might be missed.
B e f o r e a d e c i s i o n i s m a d e t o d u s t , r e d u s t , o r r e r r l o v e s n o w , i t would be desirable to know future weather conditions. T h e r e would be no point in dustingif. a large snowfall or if
s e v e r a l days of unfavourable cold weather were e>cpected. T h e 1963 triaLs demonstrated that to plan dusting operations e f f e c t i v e l y r e l i a b l e w e a t h e r f o r e c a s t s a r e r e q u i r e d .
- 7
D u r i n g t h e 1 9 6 2 a n d I 9 6 3 e x p e r i m e n t s , i t w a s o b s e r v e d
t h a t i f night-time t e m p e r a t u r e s w e n t much below freezing, t , l n e
m e l t w a t e r o n t h e dusted surface froze and on the following day t h e a v a i l a b l e s o l a r e n e r g y w a s u s e d t o m e l t t h i s n e w i c e . I n M a r c h 1 9 6 3 t h e r e w e r e s e v e r a l p e r i o d s w h e n t h e i n c o m i n g s o l a r radiation was well above average (f igure 5) but it was t o o cold for dusting to be effective.
1 9 6 4 I C E - D U S T I N G E X P E R I M E N T S A T I N U V I K
I n 1964 ice-dusting trials were undertaken at Inuvik, N. W. T. T h e p u r p o s e o f t h e s e t r i a l s w a s t o :
( a ) corrrpare several different dusting techniques at a northern s i t e w h e r e weather conditions are favourable for ice dusting; ( b ) determine the maximurn depth of penetration of different dusts
a n d t h e minirnum air temperature a t w h i c h dusting is effective"
I n u v i k was chosen as the site for these experiments
b e c a u s e during the spring melt period fresh snowfalls are usually
i n f r e q u e n t and inconring solar radiation is high. I n addition,
f a c i l i t i e s w e r e available to the Division at the Northern Research
L a b o r a t o r y , D e p a r t m e n t o f N o r t h e r n A f f a i r s a n d N a t i o n a l R e s o u r c e s ,
Inuvik"
Long Lake, situated about half way between the Inuvik
t o w n s i t e and Inuvik airport, w a s c h o s e n f o r the e>cperiments.
T h e lake is approxirnately l j miles long and one-third of a
m i l e w i d e , w i t h a n o u t l e t at the western end of the lake" F o u r t e s t a r e a s , e a c h a b o u t 5 0 f t w i d e ( 1 5 m . ) a n d s e v e r a l h u n d r e d f e e t l o n g , w e r e c l e a r e d o f s n o w o n ? 5 A p r i l b y a b u l l d o z e r . O n e a r e a , l o c a t e d n e a r t h e c e n t r e o f t h e l a k e , w a s u s e d t o c o m p a r e t h e d e p t h o f p e n e t r a t i o n o f d i f f e r e n t - s i z e p a r t i c l e s . A t t h i s s i t e d u s t s o f v a r i o u s s i z e s w e r e a p p l i e d t o p l o t s 1 0 s q f e e t i n a r e a . T h e t h r e e o t h e r t e s t a r e a s , l o c a t e d a t t h e w e s t e r n e n d o f t h e l a k e , w e r e u s e d t o d e t e r r n i n e t h e i n c r e a s e d r a t e o f m e l t i n g t h a t r e s u l t e d f r o m t h r e e d i f f e r e n t d u s t i n g t e c h n i q u e s . A t o n e t e s t a r e a t h e s n o w c o v e r w a s r e m o v e d a n d f i n e c r u s h e d r o c k s p r e a d o n t h e i c e a t a n e s t i m a t e d d e n s i t y o f 8 1 b / 1 0 0 s q f t ( 4 0 0 ern/sq,m"); at a s e c o n d a r e a t h e s n o w c o v e r o n l y w a s r e m o v e d ; a n d a t t h e t h i r d t h e s n o w w a s r e m o v e d a n d a t h i n l a y e r o f r n u d w a s p u r n p e d from the lake bottom onto the ice surface.
- 8
F i g u r e 5 a i s a g e n e r a l a e r i a l v i e w o f t h e t e s t a r e a i n t h e c e n t r e o f t h e l a k e , t a k e n o n 2 0 M a y a f t e r c o n s i d e r a b l e m e l t i n g h a d o c c u r r e d . F i g u r e 6 b , t a k e n a t t h e s a r n e t i r n e ,
s h o w s the three other test sites located rlear the lake outlet. T h e l o n g s t r i p s p a r a l l e l t o t h e c e n t r a l a r e a w e r e c l e a r e d b y t h e bulldozer to act as traps for drifting snow. The narrow t r a c k s j o i n i n g t h e c e n t r e t e s t s i t e t o t h e o t h e r t e s t s i t e s w e r e m a d e b y t h e b u l l d o z e r a s i t m o v e d f r o m o n e a r e a t o a n o t h e r .
S o r n e c r u s h e d r o c k d u s t w a s a p p l i e d t o a n e > q ) o s e d s n o w -b a n k at one of the sites, near the outlet to Long Lake, and ihe r n e l t i n g o f t h i s s n o w w a s o b s e r v e d d u r i n g t h e s p r i n g - m e l t p e r i o d .
F i g u r e 7 is a plot of precipitation, i n c o m i n g solar r a d i a t i o n , a n d maximum a n d minimum a i r t e m p e r a t u r e s r e c o r d e d at Inuvik airport, 2 0 A p r i l t o 9 June 1964. During p a r t o f t h i s p e r i o d a i r t e r n p e r a t u r e s w e r e m e a s u r e d i n a S t e v e n s o n s c r e e n l o c a t e d 4 f t ( 1 . 2 m . ) above the ice cover a t L o n g L a k e . A i r ternperatures m e a s u r e d a t t h e l a k e w e r e e s s e n t i a l l y t h e s a m e a s t h o s e r e c o r d e d a t t h e a i r p o r t .
G e n e r a l Melting Pattern I964
D u r i n g t h e p e r i o d 2 0 A p r i l t o I M a y , t h e r e w a s s o r n e r n e l t i n g o f snow where the rock dust had been applied to the s n o w b a n k " M e l t i n g w o u l d o c c u r during mid-day on a clear day w h e n t h e m a x i m u m a i r t e m p e r a t u r e w a s a s l o w a s * 5 t o * 1 0 " F ( - I 5 t o - l Z " C j ; h o w e v e r , t h i s m e l t w a t e r q u i c k l y f r o z e a t n i g h t .
T h e f i r s t r e a l l y e f f e c t i v e d a y o f m e l t a t t h e t e s t s i t e s o c c u r r e d on 2 May, with a maxirnum air ternperature of 37"F ( 3 ' C ) a n d a m i n i r n u r n a i r t e m p e r a t u r e o f l 6 ' F ( - 9 ' C ) . T h e
f o l l o w i n g day, however, with a maximum air temperature o f
3 6 " F ( 2 ' C ) a n d a m i n i m u m o f l 9 ' F ( - Z " C ) , t h e r e w a s n o m e l t i n g b e c a u s e a t r a c e o f n e w s n o w h a d f a l l e n .
D u r i n g t h e p e r i o d 3 t o l 0 M a y t h e w e a t h e r w a s u n s e a s o n -a b l y c o l d -and no melting took pl-ace -at the sites. A n analysis of a i r t e m p e r a t u r e s r e c o r d e d d u r i n g t h e w e e k o f 3 t o 9 M a y 1 9 6 4 , s h o w e d t h a t t h e 7 - d a y a v e r a g e t e m p e r a t u r e ( ! . 5 o F , - 1 3 ' C ) w a s t h e l o w e s t i n t h e p a s t l 2 y e a r s , a b o u t 1 1 F d e g r e e s b e l o w t h e l 2 - y e a r a v e r a g e . D u r i n g t h i s p e r i o d t h e c r u s h e d r o c k a n d r n u d s p r e a d o n t h e i c e p e n e t r a t e d i n t o t h e c o v e r ( F i g u r e s 8 a , 8 b ) . T h e rnelting of the dusted snowbank can be observed in Figure 8a.
- 9
E f f e c t i v e melting did not start until LZ May when the m a x i m u m a i r t e m p e r a t u r e w a s 3 9 ' F ( 4 ' C ) a n d t h e n i g h t - t i m e m i n i m u m 1 7 " t r ' ( - 9 " C ) . F i g u r e s 9 a a n d 9 b s h o w t w o o f t h e t e s t p l o t s o n ZZ May, after l0 days of rnelting. M e l t i n g o f t h e i c e cover at the test plots and the undistrubed ice cover c o n t i n u e d from 22 May through to 6 to 7 June when the ice c o m p l e t e l y c l e a r e d from the lake. A high wind aided the f i n a l clearing of ice from the lake.
C o m p a r i s o n o f Ice-melting R a t e s
T a b l e I I gives inforrnation o u the ice thickness at the d i f f e r e n t t e s t plots and for the undisturbed cover during the p e r i o d I1 May to 6 June. By 22 May it was difficult to make
i c e thickness observations o n some of the plots because the
i c e c o v e r was unsafe to walk upon. The area dusted with sand a n d t h e area flooded with mud were covered with water several i n c h e s deep, and the ice cover under the water was rotten in p l a c e s . W i t h c a r e , o b s e r v e r s w e r e a b l e t o w a l k o n p a r t s o f t h e test area that had only snow cleared from it.
B y 2 Z M a y t h e i c e c o v e r a t a l l t e s t a r e a s w a s i n a n a d v a n c e d s t a g e o f m e l t , w h e r e a s t h e r e w a s a l m o s t 3 f t ( 1 m . ) o f solid ice under the surrounding undisturbed snow cover. B y 28 May the ice had almost completely melted from the test a r e a s l o c a t e d near the outlet to the lake. B e c a u s e of surface f l o o d i n g it was difficult to colspare melting rates, but the ice c o v e r at the area dusted with crushed rock and the area flooded w i t h mud appeared to melt more rapidly than at the site where o n l y the snow cover had been removed.
T a b l e III presents information o n the depth of water
a t t h e small test areas dusted with carbon black or with c r u s h e d r o c k o f v a r i o u s s i z e s . T h e d e p t h o f m e l t w a s
i n d e p e n d e n t of the size of the crushed rock or type of material.
T h e maximum d e p t h o f water observed on Z8 May of I6 in.
( 4 0 cm) was about twice the depth observed at Ottawa in the I 9 6 2 e x p e r i r n e n t s .
C l e a r i n g the snow from the test area at the centre of t h e l a k e p r o d u c e d s o m e u n e x p e c t e d r e s u l t s . T h e w e i g h t o f t h e s n o w o n t h e e d g e o f t h e c l e a r e d a r e a a p p e a r e d t o c a u s e t h e ice to deform, r e s u l t i n g in the widening and deepening
o f t h e r m a l c r a c k s . B y 2 ? M a y t h e s e c r a c k s a t t h e e d g e e x t e n d e d t h r o u g h t h e i c e c o v e r . T h e a s s u m e d s e q u e n c e o f
i c e deformation r e s u l t i n g from the snow clearing is shown
- l 0 D i s c u s s i o n o f 1 9 6 4 O b s e r v a t i o n s
B e c a u s e o f t h e p r o b l e m s o f r e c o r d i n g i c e t h i c k n e s s a n d a s s e s s i n g t h e d e g r e e o f i l r o t t e n n e s s t r o f m e l t i n g i c e i t w a s d i f f i c u l t t o c o l r r p a r e the effectiveness of the different techniques. I t would a p p e a r , however, that removing the snow cover and dusting or f l o o d i n g the e>cposed ice with mud was more effective than just r e m o v i n g t h e s n o w c o v e r . T h e i n c r e a s e d m e l t i n g r a t e t h a t r e s u l t e d from ice dusting was considerably gr eater at this n o r t h e r n s i t e t h a n i n southern Canada"
T h e c o n d i t i o n s most favourable for ice dusting were f o u n d to be when minimum a i r t e m p e r a t u r e w a s between 25 to 3 2 " E ( - 4 t o 0 ' C ) a n d m a x i m u m a i r t e m p e r a t u r e b e t w e e n 3 9 t o 4 8 ' F ( 4 t o 9 ' C ) " I f t h e n i g h t - t i m e t e m p e r a t u r e w e n t b e l o w 2 5 " E ( - 4 " C ) , f r e e z i n g at night offset the increased rnelting during
t h e day" If the maxis1r1111 a i r t e m p e r a t u r e s w e n t above 45 to 50"F ( 7 t o I 0 " C ) t h e n o r m a l melting of the snow and ice cover produced f l o o d i n g along the shores of the lakes. I t was noted, however, t h a t dusting was beneficial as well during the period when active m e l t i n g o f t h e u n d i s t u r b e d s n o w and ice was taking place. D u r i n g t h i s period the albedo of the undisturbed surfaces was still higher t h a n the albedo of a dusted surface.
U s i n g t h e e x p e r i e n c e g a i n e d i n t h e s e e > r p e r i m e n t s , p a s t w e a t h e r records at Inuvik were examined to obtain the dates w h e n ice dusting would have first been effective. I c e dusting w a s a s s u m e d t o c a u s e a c c e l e r a t e d m e l t i n g i f t h e m e a n d a i l y a i r t e m p e r a t u r e w a s b e t w e e n 3 0 t o 3 5 " F ( - l t o Z " C l , a n d r a p i d r n e l t i n g w a s assumed to take place if the rnean daily air t e m p e r a t u r e w a s a b o v e 3 5 " t r ' . T h e p l o t o f a i r t e m p e r a t u r e d u r i n g spring break-up for Inuvik (1958 -L9631 and Aklavik ( 1 9 5 4 - 1 9 5 7 , w h e n r e c o r d s were not available at Inuvik) i s s h o w n i n F i g u r e 1 1 .
T h e s e graphs show that advancing the melting by dusting w o u l d not usually be possible much before l5 May, and that the d a t e when dusting could be expected to be effective coincides w i t h the date when normal rnelting begins. F f o w e v e r the date w h e n dusting would first be effective varies from year to year, r n 1954, dusting would not have been effective before about I June. I n 1 9 5 6 i c e d u s t i n g m i g h t h a v e b e e n b e n e f i c i a l b y 3 0 A p r i l . T h e s e v a r i a t i o n s a r e i r 6 p o r t a n t not only in planning when to dust but also i n a s s e s s i n g t h e p o s s i b l e b e n e f i t s o f i c e d u s t i n g ,
- I l
I 9 6 5 I C E - D U S T I N G E X P E R I M E N T S
I n 1 9 6 5 i c e - d u s t i n g t r i a l s w e r e c a r r i e d o u t a t t h r e e l o c a t i o n s : O t t a w a , Inuvik, and Sheardown Lake near Milne I n l e t , B a f f i n Island (Figure 1). Because the spring rnelt period o c c u r s at a different tirne at each of these latitudes it was possible f o r the author to observe the effect of ice dusting under three d i f f e r e n t c l i m a t i c c o n d i t i o n s in one season. F i g u r e 12 is a plot o f t h e a i r t e m p e r a t u r e r e c o r d s d u r i n g t h e t r i a l s f o r t h e t h r e e s i t e s .
Ottawa
T h e p u r p o s e o f the Ottawa trials was to evaluate the t e c h n i q u e of applying comrrrercial ice-dusting powders before a t t e m p t i n g trials with them later in the spring at the northern s i t e s . T h e t w o p o w d e r s t e s t e d w e r e c o l l o i d a l g r a p h i t e a n d c a r b o n powder, both suspended in water and applied as sprays.
O n 8 March carbon dust was sprayed on a test plot of a b o u t 2 0 0 s q f t ( 1 8 s q m . ) . O n 1 5 M a r c h i t w a s a p p l i e d t o a s e c o n d t e s t p l o t o f t h e s a m e s i z e . T h e s e c o n d t e s t p l o t w a s s p r a y e d again on 5 ApriI. C o l l o i d a l graphite solution was s p r a y e d on a third plot of about I0 sq yd on the same date. T h e s e s p r a y s w e r e a p p l i e d a t a r a t e o f . O . 4 I b / I 0 O s q f t ( Z O g r n / s q m e t e r ) , m i x e d a t a r a t i o o f o n e p a r t b y w e i g h t o f p o w d e r to three parts water. I f t h e density of application w a s less than this, the surface was not cornpletely blackened b u t had a rtgrey-Iikeil a p p e a r a n c e . T h i s density is about
o n e - t e n t h of the mini6s6 u s e d w h e n a p p l y i n g f i n e c r u s h e d r o c k ( T a b l e I ) .
E x c e p t f o r t h e f i r s t w e e k , a i r t e m p e r a t u r e s w e r e t o o c o l d during March for ice dusting to be eff ective (Figur e l2l. I t was not until 5 April that air temperatures w e r e h i g h e n o u g h t o i n c r e a s e t h e r a t e o f m e l t i n g . F r o m 5 t o l 5 A p r i l t h e r e w a s a p e r i o d o f r a p i d rnelting"
B y 1 5 A p r i l t h e r e w a s o p e n w a t e r o n a l l o f t h e d u s t e d p l o t s . T h e surrounding i c e c o v e r had also melted appreciably a n d o n l y t 0 i n . ( 2 5 c r n ) o f r o t t e n i c e r e m a i n e d c o m p a r e d w i t h a n i n i t i a l t h i c k n e s s o f . Z0 to 23 iln" (50-60 cm) at the beginning o f the tests. T h e melting at the plot sprayed only once, on 8 March, w a s n o t i n a s advanced a stage of melting as the o t h e r p l o t s .
- t z
T h e s e tests indicated some of the limitations o f applying
a f i n e material a s a s p r a y t o an ice cover to advance its melting. W i t h i n a f e w h o u r s t h e s p r a y w o u l d p e n e t r a t e 5 t o 8 i n . ( I 5 - 2 0 c m . ) i n t o the cover leaving an ice surface only slightly darker than t h e surrounding s u r f a c e . I m m e d i a t e l y a f t e r t h e s p r a y i n g the a l b e d o o f t h e s u r f a c e o n a l l t e s t s r a n g e d f r o m l 0 t o l 5 p e r c e n t . W i t h i n a few hours the albedo of the dusted surface was 25 to 3 0 p e r cent, compared with an albedo of 35 to 40 per cent for t h e u n d i s t u r b e d c o v e r ( F i g u r e l 3 ) . A m e l t i n g s p e l l e a r l y i n
M a r c h h a d s o f t e n e d t h e u p p e r l a y e r s of the cover and, presumably, t h i s i s o n e r e a s o n t h e s p r a y p e n e t r a t e d i n t o t h e i c e s o r e a d i l y .
N o t m u c h d i f f e r e n c e w a s o b s e r v e d b e t w e e n t h e c a r b o n p o w d e r spray and the colloidal graphite spray, both in the rate
of penetration of the spray into the cover and in tbe albedo that
r e s u l t e d .
T h e trials illustrated t h e i m p o r t a n c e o f t i m i n g o f spraying. T h e f i r s t and second sprayings, f o l l o w e d by relatively c o o l air t e m p e r a t u r e s , w e r e n o t a s effective as the sprayings on 5 ApriI, j u s t b e f o r e t h e a c t i v e i c e - m e l t p e r i o d b e g a n .
Inuvik
T h e 1965 trials at Inuvik were carried out to check the
r e s u l t s obtained in the previous year, particularly t h e effect
o n melting of only removing the snow. T h e p r e p a r a t i o n o f t h e s i t e , dusting, and snow removal were carried out with the c o - o p e r a t i o n o f M r . D i c k H i l l , M a n a g e r , N o r t h e r n R e s e a r c h
Laboratory, lnuvik.
T h e site chosen was a small lake, about one-half way
between the Long Lake site and the townsite of Inuvik. Long
L a k e was not suitable because the snow cover had been d i s t u r b e d b y s e v e r a l h u n d r e d r e i n d e e r o n l r r e i n d e e r d a y t t .
T h r e e d u s t i n g t e c h n i q u e s w e r e t e s t e d : r e r n o v i n g s n o w o n 1 y , rernoving the snow cover and applying a carbon spray, a n d a p p l y i n g the carbon spray onto the sltow cover on the ice
s u r f a c e . A t two test sites the snow cover was removed from
a n a r e a a b o u t 5 0 b y 2 0 0 f e e t ( 1 5 x 6 0 m . ) " C a r b o n s p r a y w a s a p p l i e d t o p a r t o f o n e o f t h e s e s i t e s ( 4 0 0 s q f t ) ( 3 5 s q m . ).
A t the third test site carbon was sprayed directly onto 400 sq ft ( 3 6 s q r n . ) of undisturbed snow cover. The test areas were
s e p a r a t e d by windrows of snow to protect them from drifting s n o w . F i g u r e l 4 i s a n a e r i a l v i e w o f t h e t h r e e p l o t s a f t e r m e l t i n g h a d t a k e n p l a c e .
- 1 3
S n o w w a s f i r s t c l e a r e d f r o m t h e a r e a s o n I 4 A p r i l . B e c a u s e o f n e w s n o w f a l l i t h a d t o b e r e m o v e d f r o m t h e a r e a s a g a i n o n 29 April. C a r b o n dust was first applied on I May. O n I 0 t o 1 2 M a y , 6 i n . ( 1 5 c m ) o f n e w s n o w f e l l . T h e t e s t a r e a s w e r e c l e a r e d a n d r e d u s t e d a g a i n o n l 7 M a y . B e f o r e l 7 M a y , t h e r e w e r e o n l y two days, I and Z May (Figure L?l w h e n w e a t h e r c o n d i t i o n s were reasonably favourable for melting. A f t e r I7 May the weather was quite warm and melting of the u n d i s t u r b e d s n o w a n d i c e c o v e r s c o m m e n c e d . R u n o f f f r o m t h e surrounding land caused the water level of the lake to rise a b o u t Z f t ( . 6 m . ) a n d f t o o d t h e s h o r e i c e t h a t w a s f r o z e n t o t h e b o t t o m . B y 26 May there was an open lead around the
s h o r e l i n e o f t h e l a k e a n d t h e main body of ice, containing t h e t e s t a r e a s , f l o a t e d f r e e l y "
L a r g e d r a i n h o l e s , u p t o I 5 i n . ( 4 0 c m ) i n d i a m e t e r , w e r e c r e a t e d w h e n t h e s u r f a c e w a t e r d r a i n e d f r o r n t h e s u r -r o u n d i n g t a n d ( F i g u -r e 15). MeIt wate-r in each of the test a-reas f o r m e d s i m i l a r h o l e s . D r a i n a g e t o t h e s e h o l e s t o o k p l a c e b e c a u s e t h e melting ice surface extended above the water level b y about one-tenth of its thickness (average initial ice thickness w a s 40 in. (100 cm) at all sites). D r a i n a g e c o n t i n u e d i n t o t h e h o l e s a t t h e t e s t a r e a s u n t i l t h e i c e s u r f a c e m e l t e d d o w n t o l a k e w a t e r l e v e l . B y t h i s t i m e d r a i n a g e h o l e s 6 i n . ( 1 5 c m ) i n
d i a m e t e r h a d f o r m e d a t t h e *-in. holes drilled earlier to r n e a s u r e i c e t h i c k n e s s .
T h e p a r t o f t h e i c e c o v e r i n t h e t e s t a r e a w h e r e d r a i n a g e h o l e s had developed was covered with a shallow layer of water; t h e r e m a i n i n g p o r t i o n w a s c o v e r e d w i t h p o r o u s s l u s h i c e . I n F i g u r e 1 4 t h e w a t e r - c o v e r e d p o r t i o n a p p e a r s d a r k , t h e s l u s h i c e i s l i g h t e r c o l o u r e d . T h e w a t e r - c o v e r e d s u r f a c e w i t h a l o w e r a l b e d o m e l t e d m o r e r a p i d l y t h a n t h e i c e - c o v e r e d s l u s h . T h e a l b e d o o v e r t h e w a t e r - c o v e r e d i c e v a r i e d f r o m 7 t o I l p e r c e n t . T h e albedo over the slush-covered i c e w a s q u i t e v a r i a b l e w i t h a maximum value of about 40 to 50 per cent -- close to that o f t h e s u r r o u n d i n g , u n d i s t u r b e d i c e c o v e r .
T h e ice melted at all test areas more rapidly than the u n d i s t u r b e d i c e . B y 7 June the test area cleared of snow was
3 0 p e r c e n t o p e n w a t e r , w i t h t h e r e m a i n d e r c a n d l e d i c e . T h e a r e a c l e a r e d o f snow and sprayed with dust was 50 per cent o e p n w a t e r a n d t h e r e m a i n d e r c a n d l e d i c e . T h e p l o t , w h e r e t h e spray had been applied directly to the snow cover, was
c o m p l e t e l y open. At this time the surrounding ice cover was 3 l to 33 in" thick, and the surface still had a high albedo. I t w a s n o t u n t i l l8 June that the undisturbed ice cover completely m e l t e d f r o m t h e l a k e .
- t 4
T h e f o l l o w i n g c o n c l u s i o n s c a n b e m a d e f r o m t h e I 9 6 5 I n u v i k trials:
( l ) R e m o v i n g t h e s n o w c o v e r a n d s p r a y i n g t h e e x p o s e d s u r f a c e a p p e a r e d to be a more effective method than removing the s n o w c o v e r o n l y . S p r a y i n g o n top of the snow cover also a p p e a r e d to be more effective than simply removing the s n o w c o v e r . A I I t h r e e i c e - d u s t i n g t e c h n i q u e s w e r e s u c c e s s f u l , h o w e v e r , a s p o r t i o n s o f t h e p l o t s c o m p l e t e l y m e l t e d m o r e t h a n t h r e e w e e k s b e f o r e t h e n a t u r a l i c e c o v e r m e l t e d f r o m t h e l a k e . ( 2 I T h e p a r t o f t h e t e s t a r e a w h i c h b e c a m e c o v e r e d w i t h w a t e r d e c a y e d m o r e r a p i d l y t h a n p a r t s w h e r e d r a i n a g e w a t e r d i d n o t accumulate. T h i s result might be of practical s i g n i f i c a n c e i n the application of these techniques, i. e. , parts of a dusted n a v i g a t i o n channel would be expected to decay more rapidly t h a n other parts.
( 3 ) There was no buckling or deformation of the ice cover in t h e a r e a c l e a r e d o f s n o w a s h a d b e e n o b s e r v e d i n t h e 1 9 6 4 t e s t s ( F i g u r e 1 0 ) . P o s s i b l y t h e w e i g h t o f t h e s n o w o n t h e
e d g e o f t h e t e s t a r e a w a s l e s s , w i t h l e s s t h e r m a l c r a c k i n g o f the e>cposed ice. ( L i g h t snowfalls were much rnore f r e q u e n t d u r i n g t h e 1 9 5 4 t e s t s , w h i c h w o u l d t e n d t o p r o t e c t t h e i c e c o v e r f r o r n t h e r m a l s t r e s s e s . )
( 4 I The effectiveness of a late spring snowstorm in covering t r e a t e d areas was well demonstrated. W h e n t h e d u s t i n g t e c h n i q u e i s u s e d , i t w o u l d b e n e c e s s a r y t o p l a n f o r s u c h
e v e n t s by having extra rnaterial on hand. B a f f i n Island
I n 1 9 6 5 s r n a l l - s c a l e t r i a l s a n d o b s e r v a t i o n s o n t h e m e l t i n g o f natural ice covers were made at Milne Inlet, Iocated at the n o r t h e r n e n d o f B a f f i n I s l a n d ( F i g u r e l ) . T h e s e o b s e r v a t i o n s w e r e rnade on sea ice and under different climatic conditions than the observations at Ottawa and Inuvik.
T h r o u g h the co-operation o f Mr. R. Sheardown, Baffinland I r o n Mines Ltd. , the same type of carbon dust used in the Ottawa t r i a l s was sprayed on two test plots approxirnately 2 5 0 0 s q f t ( 2 0 s q m . ) . O n o n e t e s t p l o t t h e s n o w c o v e r w a s r e m o v e d a n d t h e dust applied to the ice surface; at the second the dust was
- 1 5
I n t h e middle of June, after the active ice melt had started, t h e author visited Milne Inlet to observe the results of these trials. D u r i n g this visit limited observations o f natural ice melting were m a d e o n a s m a l l f r e s h - w a t e r l a k e l o c a t e d about 50 miles (80 kilo-r n e t kilo-r e s ) i n l a n d f kilo-r o m Milne Inlet. I n addition, s o r n e o b s e r v a t i o n s o n the melting of sea ice were made at Pond Inlet, which is about 1 0 0 miles (I60 kilometres) c l o s e r to Baffin Straits than Milne Inlet.
B y l8 June the ice cover at Milne Inlet was in an advanced s t a g e of melting. M u c h o f t h e i c e surface was covered with water w h i c h i n s o m e p l a c e s w a s s e v e r a l i n c h e s d e e p . A t t h e s p r a y e d s i t e s w a t e r o n t h e s u r f a c e w a s u p t o 2 ? i n . ( 5 5 c r n ) d e e p ( F i g u r e l 7 ) . T h e r e was no apparent difference in rate of melting at the sites a n d both were unsafe to walk upon.
I n several places on the undisturbed ice cover at Milne I n l e t sand blown from the shore had formed melt holes about 4 in. ( 1 0 c m ) i n d i a m e t e r a n d a s m u c h a s 1 5 i n . ( 4 0 c m ) d e e p . B y 2 0 J u n e t h e u n d i s t u r b e d ice at Milne Inlet was quite treacherous t o w a l k upon, with holes extending completely through the 5-ft-( 1 . 5 m . ) t U i c t i c e c o v e r "
S i m i l a r a d v a n c e d melting was observed at Pond Inlet" M u c h o f t h e s u r f a c e i c e was covered with water and the ice i r n m e d i a t e l y b e n e a t h the water was soft and porous. I n some p l a c e s s a n d h a d b e e n t r a c k e d o n t o t h e i c e b y a b o m b a r d i e r
u s e d t o b r i n g f r e s h w a t e r t o t h e c a m p f r o m a n i c e b e r g o f f s h o r e . T h e b o m b a r d i e r t r a c k s w e r e c o v e r e d w i t h w a t e r s e v e r a l i n c h e s d e e p . I n s o m e p l a c e s w h e r e t h e s a n d h a d b e e n d e p o s i t e d , m e l t h o l e s u p t o 2 f t ( . 6 * . ) d e e p h a d f o r m e d ( F i g u r e l 8 ) .
S i m i l a r t r a c k i n g o f sand onto the ice by a bombardier w a s n o t e d a t t h e s m a l l f r e s h - w a t e r l a k e ( F i g u r e l 9 a ) . B y 2 0 J u n e it was estimated that this accidental dusting had caused a b o u t l 2 i n . ( 3 0 c r n ) o f i n c r e a s e d m e l t . M e l t w a t e r p r o d u c e d b y t h i s d u s t i n g w a s a b s o r b e d i n t o t h e i c e c o v e r . T h e i c e c o v e r w a s 6 t o 6 ! f t ( 1 . 8 - Z m . ) t f r i c k a n d w a t e r d i d n o t a p p e a r i n t h e m until the bottom was at lake-water l e v e l " ( F o r this ice t h i c k n e s s , l a k e - w a t e r l e v e l w a s s e v e r a l i n c h e s b e l o w t h e n a t u r a l i c e s u r f a c e . )
A t a few places on the lake, fuel oil spilled on the ice h a d c a u s e d i n c r e a s e d m e l t i n g ( F i g u r e l 9 b ) . T h e f u e l o i l t e n d e d t o rnelt through at a uniform rate, producing a smooth, level s u r f a c e , i n contrast to sand which rnelted into the ice to varying d e p t h s , producing a pitted, uneven surface.
- 1 6 T h e r e w a s n o a p p r e c i a b l e d i f f e r e n c e o n a c l e a r d a y b e t w e e n a l b e d o m e a s u r e d o v e r a s a n d - d u s t e d s u r f a c e , a n o i l s u r f a c e , o r a w a t e r - c o v e r e d i c e s u r f a c e . T h e a l b e d o o f t h e f u e l o i l s u r f a c e w a s l 0 t o 1 2 p e r c e n t , f o r a d r y , s a n d s u r f a c e B t o I 0 p e r c e n t , a n d f o r w a t e r 6 i n . ( I 5 c m ) d e e p a b o u t I 0 p e r c e n t . T h e albedo of the natural lake ice cover varied between 5 0 t o 5 5 p e r c e n t .
O n 19 June, light sand was sprinkled on a square yard o f ice surface and the colloidal graphite was sprayed on another t e s t p l o t o f the same size. W i t h i n 4 8 h r , u n d e r c l e a r sky
c o n d i t i o n s , t h e s a n d h a d m e l t e d a h o l e 5 t o 6 i n . ( L Z - 1 5 c m ) d e e p . I n c o n t r a s t , t h e r e w a s essentially no melting on the s p r a y e d p l o t . T h e spray had rapidly penetrated the ice cover, l e a v i n g the surface with an albedo the same as the surrounding l a k e i c e . ( T h e graphite had been mixed with watet at 32" f'(0"C) a n d a p p l i e d at this temperature. ) F i g u r e 2 0 a s h o w s a v i e w o f t h e two dusted plots. T h e d u s t e d p l o t i s visible in the background; t h e sprayed plot, marked by the ruler in the foreground, p r e s e n t s a surface similar to the surrounding ice cover. F i g u r e 20b shows a r a d i o m e t e r o v e r t h e u n d i s t u r b e d i c e . P r e s u m a b l y t h e spray w o u l d h a v e i n c r e a s e d t h e m e l t r a t e a s t h e s e a s o n p r o g r e s s e d , b u t i n the earlier stages, under the prevailing c o n d i t i o n s , i t was not as effective as dusting with sand.
I n c r e a s e d rate of rnelting occurred at dusted sites on t h e f r e s h - w a t e r l a k e only when the minimum a i r t e m p e r a t u r e s w e r e c l o s e t o 3 2 ' F . I f t h e m i n i m u m a i r t e m p e r a t u r e w e n t b e l o w 2 5 " F ( - 4 ' C ) , f r e e z i n g w o u l d o c c u r and, even at this high latitude w i t h continuous 24-hr sunshine, melting because of dusting was s h a r p l y r e d u c e d .
A study of available weather records for Pond Inlet and A r c t i c Bay showed that the maximum daily air temperature d o e s n o t g o m u c h a b o v e 4 5 t o 5 0 ' F ( 7 t o I 0 " C ) d u r i n g t h e i c e -m e l t i n g p e r i o d . T h u s the heat gained by convection is usually n o t l a r g e during this period, particularly i n c o m p a r i s o n w i t h s i t e s i n the Ottawa area where air temperature c a n g o to 60 t o 7 0 ' . F ( I 6 t o 2 t ' C ) d u r i n g t h e s p r i n g - t h a w p e r i o d . A t I n u v i k , a i r t e m p e r a t u r e s f r e q u e n t l y g o o v e r 6 0 ' F l a t e i n t h e i c e - m e l t s e a s o n . T h u s , on the northern part of Baffinland, m e l t i n g d u e t o radiation from the sun is of greater importance, a n d d u s t i n g , w h i c h i n c r e a s e s the amount of radiation absorbed, will have a more significant influence on the rate of melting.
- t 7
T h e technique of clearing the snow cover frorn ice to i n c r e a s e the rate of melting would probably not be practical
i n this region. A c c o r d i n g to limited weather observations,
r e c o r d e d at a construction c a m p near the fresh-water l a k e ,
light snow and blowing snow occur quite frequently during May
a n d e a r l y June. I f these conditions are typical, i t w o u l d be d i f f i c u l t to keep e>cposed sites clear of snow. The 1965 o b s e r v a t i o n s a l s o i n d i c a t e d that the underlying ice cover had a r e l a t i v e l y h i g h albedo and clearing snow from the ice would p r o b a b l y have not appreciably increased the melting rate.
T h e raising and Iowering of the sea ice cover by the tide at Pond Inlet and Milne Inlet may affect the melting p r o c e s s by opening and enlarging cracks in the ice cover
c l o s e t o s h o r e " F i e l d o b s e r v a t i o n s a r e r e q u i r e d t o d e t e r m i n e t h e effect, if any, of tidal movement on the melting of dusted ice.
T h e following conclusions were obtained from the 1955 B a f f i n Island observations :
( 1 ) At high latitudes, under favourable weather conditions,
i c e dusting greatly increases the rate of rnelting. F o r
e x a m p l e , in 1965, if a navigation channel had been dusted w i t h a suitable dust, the ice cover at Milne or Pond Inlets c o u l d p r o b a b l y have been reduced from a thickness of 5 ft ( 1 . 5 r n " ) t o I t o 3 l t t l g - I . 0 m . ) b y z 0 J u n e .
( Z ) Even at high latitudes, with long hours of sunshine, if. m i n i 1 n s 6 a i r t e m p e r a t u r e s g o m u c h b e l o w 3 2 ' F , t h e e f f e c t i v e n e s s of dusting is significantly r e d u c e d because o f f r e e z i n g at night.
( 3 ) The observations confirmed that applying a fine dust as a s p r a y t o i c e c o v e r s t h a t a r e p o r o u s i s n o t a s e f f e c t i v e , i n t h e early stages of melt, as applying sand or similar c o a r s e r n a t e r i a l .
( 4 ) F u l l - s c a l e f i e t d t r i a l s w i l l b e n e c e s s a r y t o d e t e r m i n e t h e f e a s i b i l i t y o f extending the navigation season at this l o c a t i o n . T h e e f f e c t o f t i d e s o n t h e i c e - m e l t i n g p r o c e s s , t h e most efficient dusting pattern and technique to use for I o n g navigation channels, the effectiveness of ice dusting u n d e r a d v e r s e s p r i n g b r e a k - u p w e a t h e r c o n d i t i o n s , a r e q u e s t i o n s w h i c h c a n o n l y b e a n s w e r e d b y s u c h t r i a l s .
- 1 8 GENERAL CONCLUSIONS I n a s s e s s i n g t h e p o s s i b l e v a l u e o f d u s t i n g , t h r e e m a i n f a c t o r s m u s t b e c o n s i d e r e d : ( 1 ) w e a t h e r c o n d i t i o n s t h a t o c c u r d u r i n g t h e m e l t p e r i o d , ( Z ) s n o w a n d i c e c o n d i t i o n s , a n d ( 3 ) t h e d u s t i n g t e c h n i q u e . T h e g e n e r a l c o n c l u s i o n s , b a s e d o n t h e experience gained from the observations made during four m e l t s e a s o n s , a r e b r o k e n d o w n i n t o t h e s e t h r e e c a t e g o r i e s . B e c a u s e t h e e f f e c t i v e n e s s o f i c e d u s t i n g d e p e n d s o n w e a t h e r , t h e c o n c l u s i o n s w i l l n o t n e c e s s a r i l y b e v a l i d f o r a l l c l i r n a t i c a n d s i t e c o n d i t i o n s .
W e a t h e r C o n d i t i o n s
D u s t i n g snow or ice covers to increase the rate of m e l t i n g o f i c e i s n o t v e r y e f f e c t i v e i f t h e m i n i m u m d a i l y a i r t e m p e r a t u r e f a l l s rnuch below 32"F. T h i s c o n c l u s i o n a p p l i e s t o all latitudes. I c e dusting is thus most effective during the n o r m a l melting period" D u s t i n g rnuch before natural melting b e g i n s i s u s u a l l y n o t w o r t h w h i l e b e c a u s e t h e d u s t i n g p e r i o d i s u s u a l l y f o l l o w e d b y p e r i o d s o f f r e e z i n g w e a t h e r w h i c h w i l l f r e e z e t h e rnelt water produced" D u s t i n g c a n b e e f f e c t i v e u n d e r t h e s e c i r c u r n s t a n c e s i f t h e m e l t w a t e r i s d r a i n e d f r o m t h e a r e a . T h e o p e n i n g o f drainage ditches by dusting(3) may be an example of a s i t u a t i o n w h e r e a d e q u a t e d r a i n a g e i s a v a i l a b l e .
S m a l l a m o u n t s o f n e w s n o w , w h i c h m i g h t i n w e a t h e r r e c o r d s b e c l a s s i f i e d a s a t r a c e , c a n e f f e c t i v e l y c o v e r d u s t e d a r e a s a n d p r e v e n t i n c r e a s e d m e l t i n g b y d u s t i n g . T h i s m a y l i m i t the application of the dusting technique in regions subject t o f r e q u e n t l i g h t s n o w f a l l d u r i n g t h e s p r i n g - r n e l t p e r i o d "
A s air temperature, s n o w f a l l , a n d s o l a r r a d i a t i o n a t a s i t e v a r y g t e a t l y f r o m y e a r t o y e a r , s o w i l l t h e s u c c e s s o f d u s t i n g . V a r i a b l e w e a t h e r c o n d i t i o n s might be the factor that w i L l d i s c o u r a g e r e g u l a r , l a r g e - s c a l e , i c e - d u s t i n g o p e r a t i o n s . I n t h e U . S . S . R , , l a r g e - s c a l e d u s t i n g o p e r a t i o n s w e r e r e p o r t e d t o b e s u c c e s s f u l o n a n A r c t i c B a y i n 1 9 5 9 ( 4 ) , b u t t h e n e x t y e a r , a t t h e s a r n e s i t e , t h e o p e r a t i o n w a s o n l y p a r t i a l l y s u c c e s s f u l b e c a u s e o f d r i f t i n g s n o w a n d l o w a i r t e r n p e r a t u r e s w i t h c l o u d y c o n d i t i o n s .
_ l g
S n o w a n d I c e C o n d i t i o n s
T h e w a y i n w h i c h n a t u r a l i c e m e l t s m u s t b e c o n s i d e r e d w h e n a s s e s s i n g t h e u s e f u l n e s s o f d u s t i n g t o i n c r e a s e t h e r a t e o f s n o w - o r i c e - m e l t . F o r e x a m p l e , f r e s h - w a t e r l a k e i c e h a s a r e l a t i v e l y h i g h albedo for much of the ice-melt s e a s o n .
D u s t i n g t h e s u r f a c e , t h e r e f o r e , c a n d e c r e a s e t h e a l b e d o a n d h e n c e s i g n i f i c a n t l y i n c r e a s e the rnelting rate.
T h e depth of water that accumulates in the dusted plots can lirnit the effectiveness of dusting. The rnaximum de1>th in t h e s e e r c p e r i r n e n t s w a s I in. (20 cm) at Ottawa and about l8 to
2 4 i n . ( 4 5 - 6 0 c m ) in the Arctic. T h e r n a x i m u m d e p t h s a r e c o m p a r a b l e t o d e p t h s r e p o r t e d f o r c r y o c o n i t e s i n g l a c i e r i c e i n Greenland(5). T h e depth appears to be a function of the d u r a t i o n a n d i n t e n s i t y o f s o l a r r a d i a t i o a a b s o r b e d a t t h e w a t e r s u r f a c e .
Drainage holes can develop and extend through the i c e c o v e r a t d u s t e d s i t e s . M e l t w a t e r w i l l t h e n d r a i n t h r o u g h t h e h o l e s a n d melting will be faster than at sites where drainage w a t e r a c c u m u l a t e s . U n d e r t h e s e c o n d i t i o n s , p a r t o f a d u s t e d a r e a w i l l c l e a r o f i c e r n o r e r a p i d l y t h a n o t h e r p a r t s . T h i s r e s u l t m i g h t b e o f p r a c t i c a l s i g n i f i c a n c e i n l a r g e s c a l e i c e -d u s t i n g o p e r a t i o n s " D u s t i n g T e c h n i q u e s C l e a r i n g t h e s n o w f r o r n a n i c e c o v e r c a n i n c r e a s e t h e r a t e o f melt effectively if the snow cover is deep enough to d e l a y n a t u r a l melting and if the underlying ice cover has a n a t u r a l l y l o w albedo (black ice). U n d e r some conditions t h e w e i g h t o f snowbanks at the edge of the cleared area will
c a u s e t h e i c e t o d e f o r m a n d a c c e l e r a t e i t s d e c a y d u e t o f l o o d i n g . T h e s n o w - c l e a r i n g t e c h n i q u e s h o u l d b e l i m i t e d t o r e g i o n s w h e r e l a t e spring snowstorms a r e i n f r e q u e n t , a n d t h e s n o w c o v e r c a n b e e a s i l y r e m o v e d .
A l r n o s t any dark rnaterial applied to an ice surface will a b s o r b r a d i a t i o n a n d i n c r e a s e t h e r a t e o f melt under favourable w e a t h e r c o n d i t i o n s . T h e r n o s t s u i t a b l e p a r t i c l e s i z e r a n g e s f r o r n I t o 2 . 5 m m ( 1 ) ( . O + - . 1 0 i n . ) . T h e d e n s i t y o f a p p l i c a t i o n w i l l depend on the particle s i z e a n d h o w e v e n l y t h e d u s t c a n b e a p p l i e d . I n p r a c t i c e t h e density of application will range from 0 . 0 4 t o 0 . 0 8 l b / s q f t ( 2 0 0 - 4 0 0 g r n s / s q m . ) .
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D y e s and powders applied in the form of sprays to ice c o v e r s t h a t a r e p o r o u s a r e n o t a s e f f e c t i v e i n t h e e a r l y s t a g e s o f melt as sands or similar d u s t s because they penetrate the i c e leaving a surface with a high albedo. A s the melt season p r o g r e s s e s , h o w e v e r , s o l a r r a d i a t i o n i s a b s o r b e d b y t h e s p r a y b e n e a t h the ice surface and thus increases the melt rate. A t
s i t e s w h e r e the cost of transporting a n d a p p l y i n g d u s t i s h i g h , s p r a y s have an advantage over dusts because much less material i s r e q u i r e d .
P u m p i n g a thin layer of bottom mud onto the ice cover o f shallow lakes or rivers is an effective nreans of increasing t h e m e l t r a t e o f i c e .
T h e choice of technique will depend on cost and local s i t e conditions" L a r g e amounts of materials s u c h a s s a n d o r c o a l would be required for extensive dusting and so would have t o b e a v a i l a b l e locally to justify their use. T h e choice of t e c h n i q u e will also depend on the problem that is to be solved,
e . g . , increasing snow or glacier runoff, extending the navigation s e a s o n , o r p r e v e n t i n g i c e j a m s o n r i v e r s . P a s t w e a t h e r r e c o r d s a n d i n f o r m a t i o n a v a i l a b l e o n the problem (such as past break-up r e c o r d s , s i t e c o n d i t i o n s , e t c . ) need to be studied to determine i f possible benefits warrant the estimated expenditure. I f p o t e n t i a l b e n e f i t s d o e x c e e d a n t i c i p a t e d e x p e n d i t u r e , l a r g e - s c a l e t r i a l s m a y h a v e t o b e c a r r i e d o u t a t a s i t e , p o s s i b l y f o r m o r e t h a n one year, before the most effective technique is developed, a n d a t r u e a s s e s s m e n t o f i t s v a l u e r n a d e .
A C K N O W L E D G E M E N T S
T h e author acknowledges with gratitude the help and c o - o p e r a t i o n h e r e c e i v e d from rrrany different people and o r g a n i z a t i o n s " T h e co-operation o f p e r s o n n e l o f the Marine
S e r v i c e s , D e p a r t m e n t o f T r a n s p o r t , p a r t i c u l a r l y M r . U . J . L o r t i e , i s gratefully acknowledged" V a l u a b l e assistance was given
b y Mr. D. HilI and staff, Departrnent of Northern Affairs, I n u v i k , and Mr" R. Sheardown, Baffinland Iron Mines Limited. T h e author also wishes to thank his colleagues in the Division o f B u i l d i n g R e s e a r c h , M e s s r s . L . W . G o l d a n d G . H . J o h n s t o n f o r their advice and help in this project.
