Skull of the Danube

Skull on the Danube (16 November 2018. image by: Kaszás Gergő) 

Gergő Kaszás shared some particularly beautiful drone images of this year's and last autumn's Danubian low waters. One of the most interesting had the shape of a skull of an ancient reptile. It could have been a riddle where the picture was taken, but surely few would have guessed, because this river regulation structure made of stone is not even found in Hungary. It is part of a curved guide bank built on the left side of the island of Süttő, in Slovakia, which directs the shipping route to the coast of Süttő. In this post we will examine it not only the shape, but also for the way it was formed. .

Below Dunamocs (Moča), the stone revetment starts from the bank, then continues in the river bed with a break where the smaller branch receives some water from the main branch, until it reaches the southern side of the Süttő island. This structure has existed for at least a hundred years and partially closes off a branch of the river. It was connected to the bank by a cross dam until recently. Between 2006 and 2010, this cross dam, which used to close the tributary, was cut through. The excavated crop stones were not taken far, but were piled up in gullies on both sides, thus forming these two strange parallel stone scatters next to the "skull's" eye. 

View of the "skull" half century ago (Fentrol.hu 12. November 1969.)

Both the construction of the curved guide bank and the dismantling of the cross barrier have profoundly altered the Danube's sediment regime. The Slovakian tributary was extensively silted up, but gravel and sand bar formation also occurred on the main branch. Over time, a gap appeared in the guide bank, and a current finding its way through such a gap formed the cavity of the skull's eye. A further 'pit', a much larger cauldron, was also formed, presumably by the disruption of the cross dam. The left-hand side of the picture shows how the increased water flow 'sucked' off the sediment deposited in the foreground of the curved guide bank. This is a particularly striking phenomenon at low tide, showing that the Danube bed is constantly changing, albeit under human influence.

Translated with www.DeepL.com/Translator (free version)