Cryopediments and Cryoplanations as heritages of periglacial periods (Case Study: Eastern slopes of Shirkuh)

Cryopediment and cryoplanation are created in arid and semi-arid regions. In according to studies performed around the world, they formed in the preglacial climatic condition. Cryopediments are very gently concave erosional bench-like landforms that are usually cut into the base of valley sides or marginal slopes of highlands and mountains (Czudek and Demek, 1970; Demek, 1972). Cryopediments developed by cryogenic processes in cold climates of the periglacial climate-morphogenetic zone, mostly with the presence of permafrost (Czudek, 2012). Cryopediments develop due to the activity of a range of cryogenic processes whereby frost action, nivation and other processes and cause to retreat back scarps. Cryoplanation terraces are bedrock steps or terraces on ridge crests and hilltops. The tread or “flat” area is 10 to several hundred meters wide and long and slopes from 1 to 5 degrees parallel to the ridge crests. Cryoplanation terraces exist in many parts of the world in present or past periglacial environments. They occur chiefly in nonglaciated regions and near the general altitude of snowline. Cryoplanation terraces form by scarp retreat as the result of nivation. Surficial debris is removed across the terrace tread by mass-wasting. Terrace morphology depends mainly upon climate, bedrock type, and terrace orientation. The aim of this research is studying of periglacier landforms especially cryopediments and cryoplanation in Tange-Chenar Catchment located in the south of Mehriz city in the Yazd province. The study region is located in the west slopes of Shirkuh mountain with more than 4000 meters high between 31° 18´ to 31° 26´ of northern latitudes and 54° 18´ to 54°29´ of eastern longitudes.
Material and This research has been performed on basis of field studies and direct observation of the basin landforms. Therefore we visited the area in tow time periods involving 13/11/2015 and 30/9/2014. However, we studied topographical and geological maps, and DEM for the study area at first. Therefore, the resulted information of the maps controlled with GPS System in the field. For knowing morphology of landforms and the role of lithology in their formation, we drew geological and geomorphological maps. In addition, for studying effects of climate on the formation and development of the landforms, we evaluated climate data, especially temperature parameters in the past and present time. Thus, we drew isotherm map for cold season using temperatures data of 8 station for 14 years. Also, because of the constituent of the landforms have been created in the Pleistocene, we reconstructed temperature data foe that time using snowline and equilibrium ice-water line and drew isotherm map for that time. The study area from ground morphology and facies point of view is divided into four categories includes mountain, hill, slope terraces and pediments. Finding showed that the pediments in the region are different from warm arid and semiarid region known in the world. Although, both of them have similar morphology with the same slope about less than 12 degrees. But, they have some significant differences. For example, the cryopediments in the study area have created and developed as a result of the side valleys. Besides, deposits that cover the surface of cryopediments are not alluvial. While, pediments covered by alluvial sediment and formed due to surface water and floods. Also, on some slope can be seen one or two and sometimes three terraces which have relatively flat surfaces. The slope of their surfaces are often less than 5 degrees. Thick sediments and sometimes suitable soil have covered their surfaces. So, on some of them have been created gardens and farms. The width of the terraces varies between 10 to 100 meters. Some of them are still in developing. Most of the surfaces has located above 2000 meters. Thus, on any of these landform are not alluvial deposits.
The studying of climatic parameters shows that these landform must currently being developed. According to, we drew an isotherms map for cold season of the year. The map indicate altitudes above 2000 meters have periglacier condition especially in the cold season. Reconstructed temperature of Pleistocene period also showed that periglacial morphoclimatic system has been dominated on the most of the study area. The system has provided favorable context for physical weathering of granites and conglomerate which had formed most of the outcrop stones. Then, periglacial processes such as creep frost, nivation, congelifluction, rill erosion, dell formation and etc. caused the formation of landforms and retreating the slopes. Cryoplanations and Cryopediments are Quaternary landforms developed in the cold periods of the Pleistocene. Processes responsible for carving cryopediments were frost creep, frost heaving, nivation, congelifluction (solifluction over the permafrost table), rill erosion, piping, dell formation (dells acted as main lines of material removal) and backwearing of the back slope (Demek, 1980). Although, the morphology of cryopediment is similar to pediments in arid and semiarid region. Aridity in both environments influences weathering and slope processes, which results in similar landforms. But they create in different condition and different processes. Pediments create by surface water processes especially sheet washes. While, cryopediments and cryoplanations formed with permafrost processes. Therefore, their sediments are not alluvial. However, cryoplanations are the landforms that create in periglacier morphogenetic system with the context of stones outcrope of special. These stones in the region have been granites and conglimerates.