In former times, when the Great Aletsch Glacier was much more powerful, Lake Märjelen, this later tourist gem, was a constant threat: This typical glacier-edge lake was notorious for its frequent and unpredictable outbursts. The water masses caused devastating damage, especially in Naters between 1813 and 1915.
During high glacier levels, the water often overflowed into the neighbouring Fieschertal - mostly during the snow melt or after heavy rainfall. The floods also caused considerable damage there. For this reason, a small channel had already been dug in 1828 under the direction of cantonal engineer Ignaz Venetz, which diverted the torrents flowing from the Strahlhorn into the Märjelensee into the Fieschertal. The people of Fieschertal initially resisted a larger canal because they feared even greater damage. Only when they were promised compensation for damages did they agree. The large canal was completed in 1829.
Between 1889 and 1894, a tunnel was built to defuse the lake. But only once, in 1896, did water flow through the structure; since then, the lake level has never reached the bottom of the tunnel entrance.
Around 1988, the Tälligrat tunnel was blasted out of the rock in connection with the artificially dammed Vordersee. Today, the tunnel serves as a supply road for the "Gletscherstuba" and the reservoir. The illuminated tunnel is also useful for tourists, as they can save quite a bit of time on the way from Fiescheralp to Märjela.
Today, a small lake forms mostly in early summer when the snow melts, but it regularly runs dry. A puny remnant of the once feared and legendary glacier rim lake.
The devastating eruptions also had an impact on the legends of the affected villages. The tale of the "Rollibock" is one of the oldest in Naters, and the tale "Schoch, d'alt Schmidtja spinnt noch" (Schoch, old Schmidtja is still spinning) is also very well known.