灾变论（英语：Catastrophism）是一个地质学理论，认为地球曾经遭受许多短暂的灾难，其中有些是世界性的。这一思想可以追溯到圣经中的大洪水故事。直至十九世纪早期，仍有学者主张灾变论，例如法国学者乔治·居维叶。瑞士学者余赫泽曾根据发掘到的“婴儿化石”，认为这是被大洪水所毁灭的上一代人类的证明，但实际上那只是古代蝾螈的化石。

灾变论后来在科学界逐渐被另一派认为地球历史是长远且渐进的均变论（或称渐变论）所取代。不过到了20世纪之后，灾变论中的某些思想，又重新出现在科学当中，例如生物集群灭绝，或是月球形成理论。

Catastrophism is the theory that the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope. This was in contrast to uniformitarianism (sometimes described as gradualism), in which slow incremental changes, such as erosion, created all the Earth's geological features. Uniformitarianism held that the present is the key to the past, and that all things continued as they were from the indefinite past. Since the early disputes, a more inclusive and integrated view of geologic events has developed, in which the scientific consensus accepts that there were some catastrophic events in the geologic past, but these were explicable as extreme examples of natural processes which can occur.