Dilation. Real-world example from Mid-Ocean Ridges: Dynamics of Processes Associated with the Creation of New Oceanic Crust (emphasis is mine):
The tidal dilation of continental aquifers also acts to displace the water level within the aquifer.
According to Oxford Living Dictionaries, dilate is:
Make or become wider, larger, or more open.
1 Cann, J.R., Cann, J.R., Elderfield, H., Elderfield, H. & Laughton, A.S. (1999). Mid-Ocean Ridges: Dynamics of Processes Associated with the Creation of New Oceanic Crust. Cambridge University Press
2 "Dilate | Definition of Dilate in English by Oxford Dictionaries." Oxford Dictionaries | English. Accessed April 20, 2018. https://en.oxforddictionaries.com/definition/dilate.