Lake Ala Lombolo

Erodibility of the bottom deposits.

Ala Lombolo is a very small and shallow lake in northern Sweden. Ten sediment cores were sampled in this lake on 10 October 1997 and X-rayed in order to document the sedimentary sequence and to get data for calculating the erodibility of the upper, polluted bottom deposits. Stereoradiographs of one of the cores is shown below.

Stereoradiographs of the upper part of core AL1 from Lake Ala Lombolo. Try to study the stereoradiographs without the help of a stereoscope. Start with your nose close to the monitor, pull your face slowly away from it, and look through the image.

This coring site was situated at a water depth of 2.6 m just in front of the main inlet to the lake. The small, dark, round spots on the radiographs mark the presence of gas in bubble phase. Coarser organic material appear as larger, dark and irregulatr spots, minerogenic particles and aggregates as light spots.

Click here to get a better resolution of the stereoradiographs.

Downcore variation in content of solids in core AL1.

As exemplified by this diagram the softest sediment layers were found at a core depth of 20 - 30 cm

Calculated relationships of critical erosion velocity to void ratio for particles and aggregates with given grain size.

The two large black spots mark median values (X-ray densitometrically calculated) for the hardest and softest layer (disregarding the surface layer) with a thickness of 1 cm in the upper 0.3 m of 10 sediment cores from Lake Ala Lombolo. The hardest, less polluted layer was in 1997 situated at a median sediment depth of only 6 cm, that is above the softest, heavily mercury-polluted layers and gives therefore a certain protection against erosion of the underlying, more easily erodible sediment layers.

A larger file in Swedish.

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