Bent glacier tongues: A new look at Lliboutry's model of the evolution of the crooked Jatunraju Glacier (Parón Valley, Cordillera Blanca, Perú)

The article tackles the issue of which factors may influence the flow direction and morphological shape of glacier tongues terminating at tributary junctions to the main valley in high mountain landscapes. A very particular morphological form of a glacier tongue shows the Jatunraju Glacier in the Cordillera Blanca (Perú). It terminates in the superior Parón Valley with a prominent crooked form, embedded in a 250 m-high moraine pedestal. Lliboutry (1977) has explained the deviation of the Jatunraju Glacier tongue as a result of a proglacial lake outburst. Alternative hypothetical models on a general scale have been developed for the causes determining the morphological characteristics of glacier tongues. These are based on empirical field evidence from the Parón Valley and from glaciers located in other high mountain areas, in particular in the Himalaya Region, where glacier tongues in confluence settings are abundant. The comparative investigations demonstrate that the pronounced crooked form of the Jatunraju Glacier may not be the result of a single extreme event, but may have been produced as well by gradual processes. In a general context, the study shows that crooked glacier tongues are common landforms in other mountain regions and mainly intrinsic to debris-covered glaciers. The morphological evolution of glacier tongues may involve a polygenetic process pattern over a longer geological time period. Apart from the steepness of the valley gradient of the main valley, the former confluence from the source glacier with the main glacier during times of a more extensive glaciation is regarded as one of the dominating factors controlling the later evolution of glacier tongues in general (“inherited confluence model”).