1. 1.中国地震局地质研究所 活动构造与火山实验室，北京 100029
2.华东师范大学 地理科学学院，上海 200241
• 收稿日期:2020-01-28 修回日期:2020-03-13 出版日期:2020-04-10
• 通讯作者: 任治坤 E-mail:rzk@ies.ac.cn
• 基金资助:
中国地震局地质研究所中央级公益性科研院所基本科研业务专项“青藏高原东北缘鄂拉山与日月山断裂的构造意义”(IGCEA1803);第二次青藏高原综合科学考察研究专题“碰撞以来古地理格局与构造地貌过程”(2019QZKK0704)

### Morphology and Dynamics of Alluvial Fan and Its Research Prospects

Dengyun Wu 1( ),Zhikun Ren 1( ),Lü Honghua 2,Jinrui Liu 1,Guanghao Ha 1,Chi Zhang 1,Menghao Zhu 1

1. 1.Key Laboratory of Active Tectonics and Volcanos, Institute of Geology, China Earthquake Administration, Beijing 100029, China
2.School of Geographic Sciences, East China Normal University, Shanghai 200241, China
• Received:2020-01-28 Revised:2020-03-13 Online:2020-04-10 Published:2020-05-08
• Contact: Zhikun Ren E-mail:rzk@ies.ac.cn
• About author:Wu Dengyun (1994-), male, Dingyuan County, Anhui Province, Ph.D student. Research areas include tectonic geomorphology and active tectonics. E-mail: wdyecnu@163.com
• Supported by:
the National Nonprofit Fundamental Research Grant of China, Institute of Geology, China, Earthquake Administration “The tectonic implications of the Elashan and Riyueshan faults in NE margin of Tibetan Plateau”(IGCEA1803);The Second Tibetan Plateau Scientific Expedition and Research Program "Palaeogeographic pattern and tectonic geomorphologic process since the collision"(2019QZKK0704)

Alluvial fans can preserve historical records of sediment transport to middle and lower river systems or piedmont basins, which are considered to be sensitive recorders of climate change and tectonic activity. In this paper, the morphological characteristics, control factors and future development trend of alluvial fan are summarized and described. The main understanding is as follows: $①$ According to the gravity flow and traction flow process, fan can be divided into debris flow alluvial fan and fluvial fan. The former is formed under the action of debris gravity flow deposits, which is related to the occasional flood and burst flow in a short time. The latter is braided tributaries depositions which are gradually shallower and spread radially in the direction of fan toe under the traction water transport. $②$ The erodibility of underlying bedrock can affect the scale of downstream alluvial fan, which depends on the sediment production and store factors in the catchment. The easily eroded bedrock may produce more sediment, making the alluvial fan area larger. In the contrast, the erodibility of rocks in the source area can also affect the slope and hydrological characteristics of the valley so that more sediment is deposited in the upstream basin and the alluvial fan formed in the downstream is smaller. $③$ Tectonic activity is the pre-condition for the development of alluvial fans, which provides a space for alluvial fans depositions. Faulting in the piedmont can change the position and morphology of the ancient alluvial fan, and also cause deformation or distortion of the thick sedimentary sequence to record the regional tectonic activity. The quaternary alluvial fan sequence corresponds well to the climate change during the glacial-interglacial period. However, the influence of the flood events caused by extreme meteorological events on alluvial fan deposition should be focused on. $④$ The application of a series of new techniques and methods will help to carry out deep research on alluvial fan in the future, such as high-resolution observation technique, physical simulation experiment, and precise dating.

Fig.1 Comparison of geomorphology and sedimentology of fans (modified after references[18, 19, 43])

(a)由碎屑重力流形成的扇体，扇面坡度较陡，沉积物分选差，多含粒级较粗的砾石，夹杂砂质透镜体；(b)由高含沙重力流形成的扇体，沉积构造和结构主要由中度分选的砂质、砂砾质透镜体和薄片组成，伴生少量砾石层；(c)由牵引水流形成的河控型扇体，扇面坡度较低，沉积物分选较好，沉积层序相对简单，几乎全部由砂砾层和砂层组成，夹有古土壤和湖泊沉积；从扇顶至扇缘，不同位置的横剖面（编号：1,2,3）显示了河控型冲积扇的沉积结构
Fig.2 Cross-sections through a generalized debris flow alluvial fan, a hyperconcentrated flow alluvial fan and a fluvial fan (modified after reference [ 18 ])
(a)The alluvial fan formed by the debris gravity flow has a steep slope, poor separation of sediments, and contains coarse gravel with sandy lens； (b)The sedimentary structure and structure of the alluvial fan formed by the hyperconcentrated gravity flow are mainly composed of moderately separated sand, sand and gravel lenses and thin sections, accompanied by a small amount of gravel layer； (c)The fluvial fan formed by the traction water flow has a low slope, a good separation of sediments, and a relatively simple sedimentary sequence. It is almost entirely composed of sand and gravel layers, sandwiched by ancient soil and lake deposits. From the fan apex to the toe, cross-sections at different locations (No. 1,2,3) show the sedimentary structure of the fluvial fan

Fig.3 The relationship between the erodibility of bedrock and the area of alluvial fan(modified after reference[ 68 ])

Fig.4 Typical alluvial fans located along a normal fault at a range front(modified after reference [ 75 ])
Sourcing drainage basins are entrenched in the mountainous footwall. Triangular facets indicate the mountain front. The fans prograde towards the axial river in the hanging wall basin

Fig.5 Cross-section showing the influence of tectonic compress on the development of alluvial in the piedmont (modified after reference[ 79 ])
The alluvial fan system records the relationship between tectonic uplift and stratigraphic fold in the basin. The formation wedge into the former growing strata indicates that the tectonic uplift is a syndepositional process and its folding deformation is recorded in the deposition process of alluvial fan

Fig.6 Relationship between climate change and alluvial fan stages in piedmont of the Spartan Mountain, Greece (modified after reference[ 76 ])