نتایج جستجو برای: sand dunes

تعداد نتایج: 29226  

2015
Jiachen Zhang Yuqing Zhang Dongqing Fan Shugao Qin Xin Jia Bin Wu Dong Chen Hao Gao Linfeng Zhu Christopher J. Lortie

Vegetation patterns are strongly influenced by sand mobility in desert ecosystems. However, little is known about the spatial patterns of Artemisia ordosica, a dominant shrub in the Mu Us desert of Northwest China, in relation to sand fixation. The aim of this study was to investigate and contrast the effects of sand dune stabilization on the population and spatial distribution of this desert s...

Journal: Desert 2016

In the present study, in order to calculate the movement of sand dunes in the period between 2001 and 2010, the ASTER (Advanced Space-borne Thermal Emission and Reflection Radiometer) images were used. The training samples were obtained from the field, and the images of the years 2001 and 2010 were classified using maximum likelihood algorithm and decision making tree. The study area was classi...

2004
H. Tsoar

Sand dunes form an important and unique system that can be mobile or fixed by vegetation. The common mobility indices of sand dunes, which are related to the wind and the amount of precipitation and potential evaporation, do not work in many dune fields around the world. The reasons for that lie in the singular physical characteristics of the sandy soil. Sand has high hydraulic conductivity cau...

Journal: :Science 2006
Venkataramana Sridhar David B Loope James B Swinehart Joseph A Mason Robert J Oglesby Clinton M Rowe

Spring-summer winds from the south move moist air from the Gulf of Mexico to the Great Plains. Rainfall in the growing season sustains prairie grasses that keep large dunes in the Nebraska Sand Hills immobile. Longitudinal dunes built during the Medieval Warm Period (800 to 1000 years before the present) record the last major period of sand mobility. These dunes are oriented NW-SE and are compo...

2006
A. C. Fowler

Dunes and drumlins are examples of bedforms, geomorphological patterns in which the surface of the Earth is shaped by the erosive power of wind, water or ice. Aeolian dunes (i.e., desert dunes) are the most familiar such feature. Coastal sand dunes are a feature of common experience, and we are also familiar with the existence of dunes in deserts. Dunes are formed by the erosive power of the wi...

Journal: :Remote Sensing 2011
Doris K. Lam Tarmo K. Remmel Taly D. Drezner

Most remote sensing studies in deserts focus solely on vegetation monitoring to assess the extent of desertification. However, the application of sand dune encroachment into such studies would greatly improve the accuracy in the prediction criteria of risk-prone areas. This study applies the latter methodology for tracking desertification using sand dunes in the Kelso Dunes (in Newberry-Baker, ...

Journal: :The Geographical Journal 1898

ژورنال: کواترنری ایران 2018
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Introduction: At present, about 36% of the land surface is covered by arid and semi-arid areas, with 19% of these levels completely dry and no plant life. In Iran, between one third and one-fourth of Iran's dry surfaces are covered with Sand and Sand Dunes. The arid and semi-arid conditions of Iran have caused about 80 million hectares of Iran to be covered by desert areas, sand dunes and insi...

2011
Melany L. Hunt Nathalie M. Vriend

Booming” sand dunes have a remarkable capacity to produce sounds that are comparable with those from a stringed instrument. This phenomenon, in which sound is generated after an avalanching of sand along the slip face of a dune, has been known for centuries and occurs in at least 40 sites around the world. A spectral analysis of the sound shows a dominant frequency between 70 and 110 Hz, as wel...

2005
Klaus Kroy Benedikt Obermayer

Barchans are crescent-shaped sand dunes forming in aride regions with unidirectional wind and limited sand supply. We report analytical and numerical results for dune shapes under different environmental conditions as obtained from the so-called ‘minimal model’ of aeolian sand dunes. The profiles of longitudinal vertical slices (i.e. along the wind direction) are analyzed as a function of wind ...

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