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

太阳在岩石破裂中的作用已经被地貌学家和土壤科学家争论了100多年，没有解决方案。 最近的工作表明，昼夜加热和冷却是暴露岩石裂纹萌生的主要原因。 在沙漠和更潮湿的气候中，暴露的巨石中的大多数裂缝具有以南北为中心的优先取向，与岩石结构和形状无关。这种普遍存在的择优取向很难用定向太阳能加热以外的任何其他机制来解释。例如，由冻融或盐裂引起的裂缝应表现出随机取向。 该项目将研究和量化由于经常暴露在阳光下而在岩石中形成裂缝所需的基本物理和环境条件。方法包括：1）测量巨石表面应变和表面温度，并监测声发射（破裂）事件; 2）在沙漠和温带地区收集岩石破裂的现场数据; 3）使用现场测量和观察，用最先进的数值技术模拟裂纹扩展过程。该项目将涉及几个本科生在现场的数据和分析，提供一个坚实的基础，学习科学研究的原则。物理风化是岩石和基岩成更小的颗粒的机械破裂。它在岩石循环中起着基本的作用，通过岩石分解成沉积物，并通过随后增加岩石表面的化学风化作用。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。物理风化也被许多工作者与全球现象联系起来，如大气粉尘产生，碳循环和气候变化。此外，自然和人造材料的物理退化对人类文明产生了直接和持久的影响;从岩石坠落到混凝土桥梁和考古宝藏的退化等现象不断使人类付出生命、金钱和时间的代价。尽管它在我们星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，但是，我们对物理风化的理解存在着严重的差距。岩石的机械风化是通过一系列复杂的表面过程进行的，所有这些过程在某种程度上都取决于裂缝的产生和新鲜矿物表面的暴露。 表面裂纹的萌生和扩展将决定许多环境中岩石碎片后续断裂和迁移的速度。这项研究将为记录物理风化在塑造地球景观中的作用方面取得重大进展奠定基础。

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.