Predicting the effects of climate change on alpine rock slopes: Evaluation of paraglacial and periglacial drivers of rockfall in the European Alps

高山岩壁崩塌是对人类生命和基础设施的危害，也是岩质边坡演化的自然过程。目前存在着两种不同的假说，旨在解释岩坡演化：(1)由于冰川消融和随后的渐近适应能力下降，岩壁的副冰川调整频率增加；(2)以霜冻风化为主的适应能力处于稳定状态。气候变化将通过气温升高、霜冻风化活动和冰川面积减少来影响高山系统。假设(1)表明，由于冰川消融，落石频率增加。相反，假设(2)预计，由于最高的霜裂活动错位到更高的海拔，落石频率会降低。这两个假设都是基于从未在现场进行过测试或验证的假设。因此，岩壁未来对气候变化的适应是未知的。很少有研究集中在不同时间尺度上的冰川消融后的落石。在全新世的时间尺度上，崩塌依赖于冰川后的增加。这些发现是基于对侵蚀速度的测年和推导，没有考虑岩石墙的机械或热学特性。因此，观察到的增加不能追溯到副冰川调整或霜冻风化过程。相反，最近冰川消退区的岩石边坡侵蚀可以综合岩石墙的力学和热学性质。然而，建立频率分布的周期太短，无法就气候变化的潜在演化得出结论。这种方法在一次调查中整合了全新世和现代岩坡侵蚀。这项研究的目的是(1)量化岩壁的热状态，(2)量化力学状态的响应，并建立短期侵蚀速率。此外，该研究还将(3)加深对霜冻风化过程的了解，(4)对岩石边坡的长期侵蚀进行量化。在以空间换时间的方法(5)中，将建立一个岩质边坡侵蚀模型，将短期和长期岩质边坡破坏联系起来。实地考察工作将在瓦莱阿尔卑斯山的亨格利山谷和奥茨塔尔阿尔卑斯山的盖斯贝格山谷进行。将结合最先进的地貌、岩土和地球物理方法，包括折射地震层析成像、电阻率层析成像、陆地激光扫描、实验室霜冻风化模拟和Be-10测年，以解决研究目标。预期成果包括多年冻土和霜冻风化过程的时空分布、岩壁的短期适应、加深对霜冻风化过程的了解、霜冻风化模型、连接短期和长期岩坡侵蚀的岩坡侵蚀模型以及在气候变化和冰川加剧的背景下对岩坡未来演变的预测。

Rockfall from alpine rockwalls represents a hazard to human life and infrastructure but also a natural process of rock slope evolution. Two contrasting hypotheses currently exist which aim to explain rock slope evolution: (1) a paraglacial adjustment of the rockwalls with increasing frequency due to deglaciation and a subsequent asymptotically decline of adaption and (2) a frost-weathering dominant adaption with steady-state rates. Climate change will affect alpine systems by an increase of temperatures and a decrease of frost weathering activity and glaciated area. Hypothesis (1) suggests an increase of rockfall frequency due to deglaciation. On contrary, hypothesis (2) expects a decrease of rockfall frequency due to the dislocation of highest frost cracking activity to higher altitudes. Both hypotheses are based on assumptions which have been never tested or validated in the field. As a consequence, the future adaption of rockwall to climate change is unknown.Very few studies focus on rockfall after deglaciation on different time scales. On the Holocene time scale, rockfall is relied to increase post glaciation. The findings are based on dating and derivation of erosion rates without incorporating mechanical or thermal rockwall properties. As a result, the observed increase cannot be traced back to paraglacial adjustment or frost weathering processes. On the contrary, rock slope erosion in recently deglaciating areas can integrate mechanical and thermal rockwall properties. However, the period to establish frequency-distributions is too short to draw conclusions on potential evolution due to climate change.This approach integrates Holocene and recent rock slope erosion in one investigation. The objectives of the study are (1) to quantify the thermal regime of the rockwalls, (2) to quantify the response of mechanical regime and establish a short-term erosion rate. Furthermore, the study will (3) increase the process understanding of frost weathering and (4) quantify long-term rock slope erosion. In a space-for-time substitution approach (5) a rock slope erosion model will be developed to bridge short-term and long-term rock slope failure. Fieldwork will take place in the Hungerli Valley, Valais Alps, and in the Gaisberg Valley, Ötztal Alps. State-of-the-art geomorphological, geotechnical and geophysical methods including refraction seismic tomography, electric resistivity tomography, terrestrial laserscanning, laboratory frost-weathering simulation and Be-10 dating will be combined to address the research objectives. Expected results include the temporal and spatial distribution of permafrost and frost weathering processes, the short-term adaption of rockwalls, an increase of understanding of frost weathering processes, a frost weathering model, a rock slope erosion model bridging short- and long-term rock slope erosion and the prediction of future rock slope evolution in the context of climate change and increased deglaciation.