In streams and other turbulent water bodies the water can supercool (i.e. cool below the freezing point). When this occurs, frazil forms in the water column and anchor ice may form on the stream bed. Formation of anchor ice and its subsequent release from the bed results in sediment transport by the released anchor ice (i.e. ice rafting).
This page presents a series of video clips that show the sequence of frazil and anchor ice formation and achor-ice rafting. Each stage is shown in a video clip about 15 seconds long. For information on the underwater video system used, go here.
Please click on the images below to load ~15-second video clips.
After viewing a clip, please use the 'back' button on your browser to return to this navigation page.
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1. UNDERWATER ICE FORMATION
Frazil is the first ice to form in a turbulent, supercooled water column. This clip shows mm- to cm-sized frazil crystals suspended in the water column of a flume. The flume channel is 21 cm wide, with a water depth of 20 cm. This view is through the side of the flume. The water column is lit from above. The disk-shaped frazil crystals become visible when they are oriented in the flow to reflect light towards the camera. The frazil concentration is about 0.1% by volume. |
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2. ANCHOR ICE FORMATION
When frazil sticks to the bed it becomes anchor ice. Individual anchor ice crystals can grow to be several cm in diameter. These crystals adhere to each other, forming a mass of anchor ice that completely covers the riverbed in this video. Note the gravel buoyed above the bed by the anchor ice. |
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3. ANCHOR ICE DISTRIBUTION
This clip shows loaf-shaped anchor ice masses scattered on a cobble/boulder stream bed. Anchor ice masses are made up of agglomerations of individual ice crystals, and have very high porosities. |
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4. ANCHOR ICE BRIDGING
As anchor ice masses grow, their buoyancy increases. Eventually, the buoyancy of the ice is greater than the weight of any 'anchoring' sediment and the anchor ice lifts off the bed. This clip shows the underside of an anchor ice mass that is just lifting from the riverbed. The underside of the ice is littered with entrained gravel. |
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5. ANCHOR ICE RAFTING
Once anchor ice lifts off the bed it drifts away, ice rafting any entrained sediment downstream. |
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6. ICE RAFTED DEBRIS
As released, floating anchor ice drifts downstream entrained sediment drops out and settles back to the riverbed. This clip shows recently ice rafted debris on top of anchor ice that is still attached to the bed. This sediment will be ice rafted further downstream when the anchor ice is released from the bed. |
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7. BIG TIME ICE RAFTING
The previous clips might give the impression that anchor ice rafts only gravel. The cobble pulled from the top of the anchor ice mass in this clip weighs 2.8 kg! |
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8. AN ICE RAFTING EXPERIMENT
To determine the importance of ice rafting, we placed painted rocks in the Laramie River so we could track their movements. This clip shows one of our painted rocks, which weighs 830 grams, buoyed above the bed by a recently-released anchor ice mass. |
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