Structure and Properties of Lake Ice - Freezing of Lakes and the Evolution of their Ice Cover - page 65

Fig. 3.7 Ice sample from Lake Valkea-kotinen, southern Finland, 19 March 2013. Ice bottom on
the left side. Scale down in centimeters. Total thickness 45 cm with 5 cm of congelation ice shown
by the clear layer. Within 30 - 35 cm from the bottom there was a 2-cm slush layer illustrated by the
cut in the sample. Photograph by the author

produces snow-ice, which may form a thick layer, at extreme 90 % of the ice sheet in
Finland (Fig. 3.7 ). The source slush is a mixture of snow and liquid water available from
fl flooding,

approximately half of it is liquid water and half of it is snow. This is because the snow
layer experiences compression when it is mixed with lake water (Lepp

flooding, liquid precipitation or melting of snow. When the slush has formed by fl

ranta and Kosloff
2000). If the liquid water is from precipitation, the proportions should be about the same
but in the melt water case, the proportion depends on the daytime melt rate; however, at
most the snow accounts for about 50 %.
Snow-ice grows from top of the slush down, and then pockets of slush can be captured
inside the ice sheet (Lepp

ä

fine or medium
size, depending on the size of the snow crystals and voids between, and the orientation of
the c-axes is random. Growth of snow-ice is limited by the presence of snow and
availability of liquid water. Therefore, as has been observed (Lepp

ä ranta 2009a). In frozen slush, the crystals are

ranta 2009a), it is
possible that slush layers remain within the ice sheet and persist for several weeks. Snow-
ice inherits air inclusions from the snow layer and has lower density than congelation ice

ä