Morphodynamics of small high-mountain wadis in arid zones (on the examples of the tributaries of the upper Dades River, High Atlas Mountains, Morocco)

The paper reports on a study of the impact of morphology and lithology of small catchments on episodic river channel development in the southern High Atlas Mountains in Morocco. A detailed analysis focused on three catchments of small wadis featuring different relief and lithology along the upper, middle and lower course of the Dades River. The fieldwork combined with an analysis of topographic and geological maps and of satellite images concluded that the development of the river valley and channel structures was related to the main stages in the development of the landform in this part of the High Atlas. The channel dynamics were found to be typical of arid mountains, which was particularly apparent within a denudational-and-fluvial zone that reached up to 3,000 m a.s.l. The dominant morphodynamic system of this zone was pluvio-gravitational where episodic heavy rainfall events triggered fast displacement of stone mantle covers down the slopes and into the river channels. An analysis of the deposition zones in the lower channel reaches and on alluvial fans at the confluence of the side valleys and the main valley leads to the conclusion that the main factor, which determines the channel morphology is the impact of debris flows and heavily loaded streams and rivers. The deposited material is then transported outside the mountain zone and deposited within broad river channels. The development of the river channels in the three catchments depends on their order, morphometric property, slope lithology and the amount of material received from the slopes

Simultaneous growth releases and reductions among Populus alba as an indicator for floods in dry mountains (Morocco)

We studied the growth reaction of silver poplar trees (Populus alba) to a large flood in November 2014 in the semi-arid High Atlas Mountains, Morocco. The flood resulted in half of the studied trees developing wider tree rings in 2015 and the other half developing narrower rings in 2015, next year after the flood. For 57.1% of trees which released growth in 2015, this was the most significant increase of ring width during their whole lives (in whole tree-ring chronologies), and for 23.8% of trees which reduced growth in 2015, this was the most significant decrease of ring width. Tree-ring reductions in next year after the 2014 flood resulted from environmental stress related to burying stems with alluvia deposited during the flood. Fresh sediments cut off air access from the root system, and for some of the sampled trees, this stress was strong enough to control their radial growth. Growth releases that follow the 2014 flood are a record of trees benefitting from a sudden supply of water, a rare opportunity in dry study area, where water is usually scarce. The study demonstrates that floods in high mountains of arid zone can cause dual, opposite growth reaction of affected trees. Such dual record is characteristic for environmental impulses, which exert stress on trees, but, at the same time, improve other conditions of tree growth. Environmental events that cause simultaneous positive and negative reactions among a population of trees, like studied flood, can easily be overlooked in chronologies based on average widths of tree rings each year. For trees affected during studied flood arithmetical mean of ring widths in 2015 is average and does not stand out from arithmetical means for other years. However, when analysed in detail, the year 2015 is significantly different from other years, as is demonstrated by high values of dispersion indicators (standard deviation and coefficient of variation) calculated for all sampled trees. This study demonstrates that following the standard procedure (developing tree-ring chronology from average ring widths) is not a reliable solution for reconstructions of environmental impulses which cause dual, opposite reaction among sampled trees. Even strong events of this type will not be emphasised in standard chronologies, which can lead to underestimating frequency and magnitude of processes and, in the case of floods, to underestimating hazard and risk

Seasonal and spatial variability of morphodynamic of slopes within snow avalanche starting zones in the Tatra Mountains

Abstract. The paper aims to examine morphodynamic of slopes within the snow avalanche starting zones in the Tatras. The analysis of mophodynamic is based on results of four years monitoring of slope surface changes at 8 study sites. It is focused on comparison of slopes activity in the winter and summer seasons. The results of the study were examined taking in the consideration meteorological conditions during the study period and the relief. It was found that relief in the Tatras favours snow avalanche occurring. In the period without snow avalanches secular morphogenetic processes modified slopes within the snow avalanche starting zones. As a result, the material of the slope covers were triggered and moved in a chaotic and random manner, as well as accumulated. The sites of erosion and accumulation of material are varied in time and space within the snow avalanche starting zones. Generally, erosion is the main effect of secular morphogenetic processes

Surge-type Uisu glacier and its undisturbed forefield relief, Eastern Pamir, Tajikistan

The surge-type Uisu glacier and its forefield in the Tajik part of Eastern Pamir are described. To this end, 1977–2019 Landsat satellite imagery, the DEM, and a high-resolution orthophotomap were used, and detailed geomorphological mapping was carried out. The results show that the present-day position of the terminus of the studied glacier results from a surge that occurred before 1947. Currently, the glacier is losing mass. However, despite the visible characteristics of its thawing, the extent of the terminal zone has remained stable for several decades. Outside the glacier, there are no glacial landforms. This indicates that advances of surging glaciers may not create any surge-diagnostic features in their forefields. On the other hand, the genesis and interactions of landforms can reveal glacier surge, even in the absence of terminal and lateral glacial landforms