v.

become steeper

"The mountain side has steepened"

make steeper

"The landslides have steepened the mountain sides"

Patent watch: the patent cliff steepens.
The patent cliff steepens
Exploring Broadband GRB Behavior During gamma-ray Emission
Using Radio Halos and Minihalos to Measure the Distributions of Magnetic Fields and Cosmic-Rays in Galaxy Clusters
Investigation of a ‘transonic resonance’ with convergent–divergent nozzles
Ten Caveats in Keratorefractive Surgery
The radio-ultraviolet spectral energy distribution of the jet in 3C 273. A&A 431, 477-502
Dependence of the outer density profiles of halos on their mass accretion rate
Simple mathematical models with very complicated dynamics
Bifurcations and Dynamic Complexity in Simple Ecological Models