Astrocytes are an essential part of the brain active milieu and generate complex spatiotemporal patterns of calcium activity during animal behavior. The properties, mechanisms, and physiological relevance of these patterns are still poorly understood. Here, we performed two-photon calcium imaging in cortical astrocytes expressing cyto-GCaMP6f in head-fixed mice running on a rotating platform. In each imaging frame, suprathreshold calcium activity regions (segments of spatiotemporal calcium events) were detected. We analyzed ΔF/F, total active area, mean segment area, and segment density during episodes of animal locomotion. The density of segments increased at the beginning of the episodes. Then, the segments started to grow, eventually merging before splitting apart after the locomotion ended. The spatial pattern of population calcium dynamics largely reproduced from one locomotion episode to another. Within this pattern, some regions tended to activate earlier than others. Such temporal heterogeneity may reflect specific temporal properties of calcium dynamics in individual astrocytes. In individual cells, calcium activity first appeared in the distal processes. Then, if it reached a threshold, it triggered a calcium surge in proximal astrocytic branches that integrated to somata, where it was further amplified (somatic surge). Notably, the somatic surge threshold was not reached during each locomotion episode, adding complexity to the population calcium response. The work is supported by the Russian Science Foundation (grant 20-14-00241).