What does the term "sag" refer to in the context of the Caloris Basin?

In the context of the Caloris Basin, the term "sag" refers to the crust straining under the weight of lava. The Caloris Basin is a large impact feature on the surface of Mercury, and its formation involved a significant impact that not only excavated material but also allowed for volcanic activity to occur afterward. As lava filled the basin, the added weight caused the surrounding crust to sag, creating depressions or alterations in the terrain's structure.

This sagging indicates the dynamics of how the crust interacted with the volcanic processes and how it responded to the different stresses applied by the weight of the erupting lava. The weight can lead to downward deformation, reflecting the interplay between impact geology and volcanic activity in that region. Understanding this process is crucial for comprehending planetary geology and the history of Mercury's surface.