Collaborative Research: Determining the role of insolation in the mechanical breakdown of rock

100多年来，地貌学家和土壤科学家一直在争论太阳在压裂岩石中的作用，但没有得到解决。最近的研究表明，白天的加热和冷却在很大程度上导致了暴露岩石的裂缝萌生。在沙漠和更潮湿的气候条件下，裸露的巨石中的大多数裂缝都有以南北为中心的优先方向，与岩石的结构和形状无关。这种普遍存在的优先取向，除了定向太阳能加热之外，很难用任何其他机制来解释。例如，冻融或盐碎裂引起的裂缝应该表现为随机方向。该项目将检查和量化岩石由于反复暴露在阳光下而形成裂缝所需的基本物理和环境条件。方法包括：1)用仪器测量岩石的表面应变和表面温度，并监测声发射（开裂）事件；2)收集沙漠和温带地区岩石裂隙的野外资料；3)利用现场测量和观测资料，利用最先进的数值技术模拟裂纹扩展过程。该项目将由几名本科生参与实地数据和分析，为学习科学研究原理提供坚实的基础。物理风化是指岩石和基岩被机械分解成更小的颗粒。它在岩石循环中起着基本的作用，通过岩石分解成沉积物，并通过随后增加的岩石表面暴露于化学风化。物理风化也决定了山坡上沉积物的产生和沙漠路面的形成。许多研究人员认为，物理风化也与大气粉尘产生、碳循环和气候变化等全球现象有关。此外，自然和人造材料的物理退化对人类文明具有直接和持久的影响；从岩石坠落到混凝土桥梁和考古宝藏的退化，各种现象不断耗费人类的生命、金钱和时间。然而，尽管它在地球的表面过程和社会基础设施中发挥着广泛而重要的作用，但我们对物理风化的理解仍存在重大差距。岩石的机械风化是通过一系列复杂的表面过程进行的，所有这些过程都以某种方式依赖于裂缝的产生和新矿物表面的暴露。在许多环境中，表面裂纹的萌生和扩展将决定随后的破裂和岩屑运移的速度。这项研究将为记录物理风化在塑造地球景观中的作用奠定重要的基础。

The role of the sun in fracturing rocks has been debated by geomorphologists and soil scientists for over 100 years without resolution. Recent work indicates that diurnal heating and cooling are largely responsible for crack initiation in exposed rocks. The majority of cracks in exposed boulders in both deserts and more humid climates have preferential orientations centered on north-south, independent of rock fabric and shape. Such a ubiquitous preferential orientation is difficult to explain by any other mechanism other than directional solar heating. Cracks caused by freeze-thaw or salt shattering, for example, should exhibit random orientations. This project will examine and quantify the fundamental physics and environmental conditions required for cracks to form in rocks due to recurrent exposure to the sun. Methods include: 1) instrumenting a boulder to measure surface strain and surface temperature, and to monitor acoustic emission (cracking) events; 2) collecting field data of rock fractures in desert and temperate sites; and 3) using the field measurements and observations to model the process of crack growth with state-of-the-art numerical techniques. The project will involve several undergraduate students in the field data and analysis to provide a frim foundation for learning principles of scientific research.Physical weathering is the mechanical breakdown of rocks and bedrock into smaller particles. It plays an elemental role in the rock cycle, through the breakdown of rock into sediment and through the subsequent increased exposure of rock surfaces to chemical weathering. Physical weathering also dictates the production of sediment on hillslopes and the formation of desert pavements. Physical weathering has also been linked by many workers to global phenomena such as atmospheric dust production, carbon cycling, and climate change. In addition, the physical degradation of natural and man-made materials has a direct and persistent impact on human civilization; phenomena ranging from rock fall to the deterioration of concrete bridges and archaeological treasures continuously cost humans lives, dollars and time. Despite its broad and significant role in surficial processes and societal infrastructure of our planet, however, there has been a critical gap in our understanding of physical weathering. The mechanical weathering of rock proceeds by a complicated suite of surface processes, all of which depend in some way on the creation of cracks and the exposure of fresh mineral surfaces. Surface crack initiation and propagation will determinethe pace for subsequent fracture and transport of rock debris in numerous environments. This research will build a foundation for significant gains in documenting the role of physical weathering in shaping Earth's landscapes.