Final answer:
During warmer temperatures in summer, the expansion of materials due to thermal stress can cause existing cracks to close as the surrounding material expands. However, uneven expansion or excessive stress might also result in new or further cracking.
Step-by-step explanation:
When temperatures increase during the summer, materials expand due to thermal stress. This phenomenon can cause cracks to close as the material around them expands. For example, the thermal expansion of construction materials like concrete in roadways can lead to buckling if there are not enough expansion joints, while power lines may sag due to the increase in temperatures. However, depending on the material and the condition of the crack, this expansion could also lead to further cracking if the expansion is uneven or if stresses become too great.
In the case of mudcracks or desiccation cracks, which often form in clay-rich sediments, they get wider at the top and narrower at the bottom. These cracks may appear to close as well when the sediment expands with moisture during warmer seasons. However, if the sediment expands unevenly, new cracks can form.