Drift block
A drift block is a large piece of rock that, embedded in large clods of drift ice , has often been transported over great distances. When it comes to glacier transport, one speaks of boulder .
River transport
On the mainland , when the river freezes through in winter , blocks trapped in the ground ice that floated up with the ice when the river thawed in spring, drifted fluviatilely and were deposited in gravel areas . These blocks are too heavy for transport as towed cargo ( bed load ). The seasonally thick ice cover necessary for freezing and transport turns drift blocks into paleoclimate witnesses of cold periods . In the middle latitudes they are characteristic companions of cold-age river deposits, the formation of which is placed in a periglacial climate with widespread permafrost .
These blocks are particularly conspicuous in the lignite mining areas, such as in the Rhenish lignite mining area in the Lower Rhine Bay as part of the Rhine-Maas Delta , where they close in the open-cast mines that reach up to 400 m below the soil horizon with the clearing of the quaternary cover layers overlying the lignite Days to be promoted.
The rocks transported from different mountain ranges in the river system make it possible to create a geological nature trail at the place of their deposition with information on their various areas of origin.
Marine transport
Drift blocks can also have been transported by marine drift ice. They now appear on the shore zones near the sea, which are now dry after the post-glacial uplift and the fall in sea level. Drift blocks can weigh several tons. They will be happy as a natural memorials, art material, markings and eye-catching but also used as fences and boundary stones, such as in the restoration of Pulheim creek .
Delimitation and special features
Drift blocks are often indiscriminately referred to as boulders . Boulders are boulders that are transported through glaciers and are usually deposited near the surface. A specialty are the tertiary quartzites , some of which are still found in situ as quartz sandstone layers, but which were also easily broken up and then drifted through water and (ground) ice.
A special feature are the dropstones , which were also transported by the glacier / sea ice and loosened from this by thawing , which hit the sediments and clearly disrupted the layers.
Individual evidence
- ↑ Geo-Lehrpfad Nettetal (accessed January 2012)
- ↑ ( online in the Google book search) Hans Murawski, Wilhelm Meyer: Geological Dictionary , Spectrum, Heidelberg 2004, ISBN 978-3-8274-1445-8 . P. 63
- ↑ Drift blocks near Meerbusch ( Memento of the original from December 13, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (Accessed Jan. 2012)
