Granule Ripples in the Kumtagh Desert, China: Morphological and Sedimentary Characteristics, and Development Processes. Issue 5 (16th May 2022)

• Record Type: Journal Article
• Authors: Han, Qingjie; Qu, Jianjun; Zu, Ruiping; Zhang, Kecun; Liu, Benli; Xie, Shengbo; Niu, Qinghe; Tan, Lihai
• Is Part Of: Journal of geophysical research. Volume 127:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-16
• Subjects: Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2021JF006448
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: Granule ripples are widespread on Earth and are a fundamental component of dryland sedimentary systems, but the relationship between their wavelength and surface particle size is unclear; in addition, their sedimentary bedding and granule ripple development are incompletely understood. In this study, we examined the relationship between granule ripple development, morphology, and the surface grain‐size distribution. We measured the morphology and particle‐size distribution of granule ripples in China's Kumtagh Desert, and found an exponential relationship between ripple wavelength and average crest particle size, which contradicts previous results. We hypothesize the ripples resulted from creep of coarse particles caused by saltation impacts, accompanied by decreasing bed elevation, leading to crest migration and increased crest height. The size composition and wind regime determined the movement mode of particles, which controlled ripple development and size, but dry–wet and freeze–thaw cycles also contributed. We established a new conceptual model for the development of large granule ripples. Sand ripples and small granule ripples develop similarly, but large ripples did not form from merger of smaller ripples. We report for the first time that particles between 2.3 and 4.7 mm in diameter were missing in the ripple crests (confirmed in wind tunnel experiments). This gap affects the particle movement mode. Since the threshold wind speed for particle saltation at 4.7 mm approaches the regional maximum wind speed, quantifying the missing particles may permit prediction of regional maximum wind speeds, and has practical significance for identifying wind conditions elsewhere, including the surface of Mars. Plain Language Summary: Granule ripple landforms develop under strong winds. Understanding their dynamics and characteristics better would reveal how near‐surface wind and sediment characteristics control sediment transport and the development and evolution of Aeolian landforms. We investigated granule ripple morphological characteristics and their range of particle sizes in China's Kumtagh Desert. We found a new relationship between particle size and ripple wavelength, and demonstrated that the largest ripples didn't form from merger of smaller ripples. Our results reveal a new conceptual model for large granule ripple development. We report for the first time that particle sizes from 2.3 to 4.7 mm were missing in the ripple crests (confirmed in a wind tunnel). The particles larger than 4.7 mm can only roll along the surface, whereas particles smaller than 2.3 mm can both roll and jump. The size gap represents a transition between the two movement modes. The particle movement mode is determined by the particle size and wind regime, which control granule ripple development and size, but dry–wet and freeze–thaw cycles also contributed. This phenomenon was missed in previous research, but may let us predict regional maximum wind speeds without needing to monitor these speeds in the field. Key Points: We found a new quantitative relationship between granule‐ripple wavelength and crest particle size Our results represent a new conceptual model for large granule ripple development Particles of a certain size were missing from the ripple crests, and this provides a new method for quantifying maximum wind speeds