TheRiss glaciation,Riss Glaciation,Riss ice age,Riss Ice Age,Riss glacial orRiss Glacial (German:Riß-Kaltzeit,Riß-Glazial,Riß-Komplex or (obsolete)Riß-Eiszeit) is the second youngestglaciation of thePleistocene epoch in the traditional, quadripartite glacial classification of the Alps. The literature variously dates it to between about 300,000 to 130,000 years ago and 347,000 to 128,000 years ago. It coincides with theSaale glaciation of North Germany. The name goes back toAlbrecht Penck andEduard Brückner who named this cold period after the riverRiss inUpper Swabia in their three-volume workDie Alpen im Eiszeitalter ("The Alps in the Ice Age") published between 1901 and 1909.
The Riss glaciation was defined by Penck and Brückner as the Lower (Niedere) or Younger Old Moraines and Old Terminal Moraines High Terraces (Jüngere Altmoränen und Alt-Endmoränen-Hochterrassen). Thetype locality lies nearBiberach an der Riß where the end of the northeasternRhine Glacier stood. Results gained from over a century of research show that in almost all glacial periods, several ice advances took place. Today it is thought that there were, in all, at least eight[1] to fifteen ice advances.[2] In the Riss stage, too, there were several advances of the ice sheet, so that it can be divided intointerstadials (ice retreats) andstadials (ice advances), and at least one hitherto unnamed warm period.[3]
The present-day division differs from the original Penck classification. The beginning of the Riss ice age, according to the 2002 Stratigraphic Table of Germany, was the end of theHolstein interglacial (known as theMindel-Riss interglacial in the Alpine Foreland and corresponding to theSamerbe,Thalgut,Praclaux andLa Côte). Its end is the start of theEem interglacial (Riss-Würm interglacial). It is thus roughly contemporaneous with theSaale glaciation of the North German glacial sequence. The Riss is paralleled byMIS 6, 8 and 10, which would therefore place it about 350,000 and 120,000 years ago.[4] Excluded from the Riss glaciation is the so-called Old Riss (Ältere Riß),[5] the time of the greatest ice advance in the Alpine region: today it is referred to as theHaslach-Mindel complex (in Bavaria and Austria), Hoßkirch complex (in Baden-Württemberg) or Great Glaciation in Switzerland.
The classification of ice ages in Switzerland varies from that used in the Bavarian and Austrian Alpine Foreland. The glaciation complex between the end of the Holstein and the beginning of the Eem interglacials is referred to as the Penultimate Ice Age and the Great Glaciation.[2] It is divided into two additional interstadials, the so-called Double Holstein Event of Meikirch (doppelte Holstein-Vorkommen von Meikirch), which is not identical, however, with the Holstein interglacial.[6]
During the period of maximum glaciation, ancient man (Homo heidelbergensis – later theNeanderthals) retreated behind the permafrost boundary and, in the warmer periods, spread beyond it to the north and northeast. Not until the Weichsel-Würm ice age did modernCro-Magnon man settle these regions, in about 40,000 BC.
At the beginning of the Riss ice age almost all of today's Alpine river valleys were created. The glaciation of the Alps, even before the Holstein interglacial and towards the end of the major glaciations, resulted in glaciers advancing in several phases far into the Alpine Foreland, further than all other known ice sheet advances,[5] and the main glaciers had established themselves along today's river valleys. During the Riss, glaciers advanced into the Bavarian and Austrian Alpine Foreland probably four times. The first two advances have not been confirmed with certainty because they are overlaid by the two stadials at the end of the Riss glaciation that extended well to the north.[7]
The ice sheet advances of the cold period were mostly well beyond theglacial lake of the previous ice sheet. In most areas, the Rissterminal moraines have formed as low embankments, for example in the area of theInn Glacier, theIsar-Loisach Glacier, theIller Glacier, and in the area of the westernRhine Glacier. In thetype region in Biberach there is a clear, but rather atypical double moraine ridge, also atypical is the double terrace here, which is probably due to heavyerosion as the meltwater runoff moved from theWellheim Dry Valley [de] andAltmühl valley into the present dayDanube valley, a process that took place during the Riss glaciation. The double ridge of the type region (Doppelwallriß, with an outer and inner ridge) is a result of two superimposed sequences of glacial deposits which indicates that the Riss was subdivided into at least two stadials.
In the west theRhône Glacier covered large parts of theSwiss Plateau and reached as far north as the northernFolded Jura and as far south asLyon. To the northeast, it transitioned without any sharp demarcation into theLinth Glacier andReuss -Aare Glacier; only theNapf area remaining ice-free. Further to the northeast, the Reuss-Aare Glacier combined with the Rhine glacier. This extended north beyond the present-dayRiver Danube to the area of theSwabian Jura. In Bavaria, the Riss moraines form a little subdivided countryside without bogs and lakes, where they are not covered by the younger deposits of theWürm glaciation. The gravels associated with the Riss moraines form the present high terraces of the Danube tributaries.[5]
During the Riss, theSalzach[8] andDachstein glaciers were somewhat smaller than during theGünz andMindel glaciations,[9] the latter extending in each case to the Hausruck and Kobernauß Forest ridge (subalpine molasse).
The cold and warm periods of theQuaternary in the Alpine region | ||
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