Weathering processes prepare and trigger rockfall, which is a key agent of alpine landscape evolution and a hazardous process. The relative importance of different weathering processes is hard to decipher; nevertheless, current knowledge assumes a dominant role of frost cracking in eroding alpine rockwalls. This study uses a laboratory approach to simulate volumetric expansion and ice segregation in four alpine rock samples, monitors crack deformation, and quantifies frost weathering efficacy. Our results show that short‐term volumetric expansion in cracks provides stresses up to 10 MPa over hours, while long‐term ice segregation causes stresses of 1 MPa over days. While volumetric expansion in fall can reach critical fracture levels, volumetric expansion in early summer and ice segregation rather approaches subcritical fracture propagation levels. We conclude that subcritical crack propagation is the dominant antecedent process of rockfall initiation, which can be amplified by rare critical cracking due to volumetric expansion. Plain Language Summary Weathering processes reduce the strength of alpine rockwalls over time and can cause rockfall events. It is widely assumed that the freezing of water to ice is the dominant weathering process. Theoretical stresses exerted by frost weathering processes are higher than the strengths of the strongest rocks. Unfortunately, freezing in nature occurs often in combination with wetting and drying or cooling and the effects of freezing are hard to decipher from these processes. Therefore, we simulate the freezing of rock samples in the laboratory, where we can control conditions and try to isolate the freezing effects. For our simulations, we cut an artificial crack into a rock sample, fill this crack up with water, and cool the rock to freeze the water infill to ice. Frost weathering works by short‐term volumetric expansion during freezing of water or long‐term ice segregation. Both processes produce stresses that result in crack widening which we record. Our results show that the ice stresses are far below the strength of rocks. To crack the rock, you need repetitive freezing that with time increases the length of the crack rather than one big freezing event breaking the rock at once. Key Points Short‐term volumetric expansion and long‐term ice segregation mostly produce ice pressures below intact rock strength Generated ice stresses are below intact fracture toughness of rocks and frost weathering proceeds by subcritical cracking Frost weathering processes in conjunction with thermomechanical stresses will respond to climate change