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Planetary aeolian geomorphology

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  • Zhibao DONG, Chao LI, Ping LÜ, Guangyin HU
    Advances in Earth Science. 2021, 36(2): 125-138.

    Aeolian landforms are divided into two categories: wind deposition landforms and wind erosion landforms. The former refers to various types of sand dunes with their shapes being determined by the spatio-temporal variation of wind erosion and deposition. Wind erosion may play a significant role in reshaping the cumulated dunes which results in the formation of eroded dunes. This discovery is contrary to traditional understanding, therefore, eroded dunes have been ignored for a long time. However, many Martian dunes with subtle differences from dunes on the earth due to limited sediment supply have been found. We reviewed the description of eroded dunes by French M. Mainguet, and conceptual framework of controlling factors on dune morphology, and then pointed out clearly the necessity of studying eroded dunes. After systematic study on Martian dunes, we found ten types of eroded dunes, and then analyzed the morphology, development environment and possible formation mechanism. The vast saline-alkali land in the arid area of the earth which is similar to the limited sand supply environment on Mars is most likely to develop eroded dunes. Based on this, it can be inferred that eroded dunes are common on the earth, and the study on them is of great significance to the development of aeolian geomorphology theories and the Mars exploration in China.

  • Zhibao Dong,Lü Ping,Chao Li,Guangyin Hu
    Advances in Earth Science. 2020, 35(10): 1006-1015.

    Large Ripples (LRs) on Mars come into the subject of researchers with the acquisition of high resolution image data. LRs are a kind of aeolian bedforms with meter-scale wavelength, and outstanding features of their morphology, bedform patterns, mobility and formation processes. However, due to the limited exploration data, especially the lack of high resolution image data, the research scope and depth are extremely limited, which leads to the long-term neglect of their uniqueness, therefore, researches simply consider them as common sand ripples on Earth. Following the geomorphology law and based on the existing limited research, this paper introduces the morphology, sedimentology and formation mechanism of LRs, and discusses their potential research significance. Compared with ordinary sand ripples, LRs are larger with sinuous and sharp crest lines, asymmetric topographic profiles, the downwind slope angle is much bigger than that of upwind, and slip faces are marked by the presence of grainflows and grainfalls. LRs have strong mobility with obvious longitudinal extension of ridges, and the lateral migration is very small. They have various orientations and network patterns which can be used to inverse the complex wind regimes over a long period of time. Three hierarchical order aeolian bedforms of sand ripples, large ripples, and sand dunes can co-exist. Preliminary explorations show that the sedimentology of LRs is the well sorted fine-to-medium sand. Three formation hypotheses were proposed for LRs: dune hypothesis, impacting hypothesis and fluid-drag hypothesis, with more evidences supporting the fluid-drag hypothesis. LRs are different from normal sand ripples, and their uniqueness is of great significance to comprehend Martian aeolian geomorphology, environmental characteristics, and revolution history, and therefore, they are worth making an intensive study of.

  • Zhibao Dong,Lü Ping,Chao Li,Guangyin Hu
    Advances in Earth Science. 2020, 35(9): 902-911.

    Wind streaks with two-dimensional plane shapes are a collective term for a variety of aeolian features that display distinctive albedo surface patterns and they do not have three-dimensional shape. Wind streaks are widely distributed on Mars, and are good proxy indicators of the surface wind regime, and even of global circulation patterns on Mars. However, the study on wind streaks has been largely ignored for a long time. Based on published studies, this paper summarized the types, morphology and formation mechanism of wind streaks. According to the relationship between albedo and obstacles, wind streaks can be divided into six basic types: bright wind streaks, dark wind streaks, mixed-tone wind streaks, splotches and related wind streaks, dune shadow wind streaks and frost wind streaks, of which the bright and dark streaks are the most common and representative, for they are the most abundant types of variable features on Mars. Wind streaks are primarily distributed in the latitudinal zone between 60°S and 60°N with little difference among different types, and they have many shapes such as tapered, fan, oval and parallel shapes due to the diverse obstacles. Considering the relationship between sediment characteristics and aeolian erosion and deposition, bright wind streaks are generally depositional with a consensus and dark streaks are erosional with a controversy. In the absence of Martian meteorological observation data, the retrieval of surface wind regime based on the orientation of wind streaks has good reliability, which helps to understand the modifications of Martian surfaces by wind in the geological context.

  • Zhibao Dong,Lü Ping,Chao Li,Guangyin Hu
    Advances in Earth Science. 2020, 35(7): 661-677.

    Transverse Aeolian Ridges (TARs) are among the unique aeolian bedforms of Mars, which witnessed a series of investigation for the last two decades thanks to the high-resolution remote sensing data. This paper summarized the understanding with respect to distribution, morphology, sedimentology, formation hypotheses and formation time of TARs. It is suggested that TARs are a kind of aeolian bedforms with meter-scale height and decameter-scale wavelength. TARs are primarily distributed in the equator and low-latitude regions, being rare in high and mid-latitude regions, and more popular in the south hemisphere than in the north hemisphere. Higher albedo and symmetric cross-sections are the most outstanding features of TARs, being analogous to the megaripples and reversing dunes on the Earth. The grain-size distribution of TARs’ sediments is generally bimodal, with granule cover and low thermal inertia. Three formation hypotheses were proposed for TARs: Megaripple hypothesis, reversing dune hypothesis and dust induration hypothesis, with more evidences supporting the megaripple hypothesis. Similar to dunes, TARs are geologically recent morphology on Mars, but generally predate dunes, formed in the last few million years so that most TARs are indurated or lithified and are immobile. However, contemporary mobileTARs are also developed in some regions. The unique features of TARs make them the mostenigmatic aeolian bedforms of Mars. It is proposed that high-resolution information on TARs sedimentology and integrated regional surveying should be listed in the priorities of future Mars exploration with respect to TARs study.

  • Zhibao Dong,Lü Ping
    Advances in Earth Science. 2019, 34(10): 1001-1014.

    The exploration of "Deep Sea, Deep Earth and Deep Space" provides opportunities and challenges for the development of geoscience, and geographical science begins to meet the climax of deep space exploration represented by Mars. In China, Martian exploration will be launched in 2020, which will carry out global and comprehensive surrounding exploration of Mars, patrol detection in some local areas, researchers need to be well prepared for the study of planetary geosciences including aeolian geomorphology based on these coming data. Aeolian geomorphology is divided into three stages based on the development history and trend: classical research focusing on single dune observation, modern research with earth system ideology and future research mainly on extra-terrestrial planets. The characteristics of each developing stage were summarized, and we believe that the planetary aeolian research will come naturally. Then, the development and achievement of planetary aeolian research are summarized, the existing problems and future developing trend were also discussed here. Study shows that there are many types of aeolian landforms on Mars, Venus and Titan, and the aeolian process is the most active modern surface process. Aeolian geomorphology in different planets has good similarity, but the difference is also obvious, which means that they have similar formation mechanism, but different formation and evolution conditions, therefore, the theory of aeolian geomorphology will be improved and enriched gradually through the comparative study on different planets. There are obvious advantages in revealing the formation laws and mechanism of aeolian geomorphology in extraterrestrial planets because of the simple formation conditions, and the research of aeolian geomorphology in the era of deep space exploration is in the ascendant.