The answer to 'retaining wall erosion' is that common causes include poor drainage, soil erosion, freeze-thaw cycles, and improper construction. Symptoms include cracks, leaning, or bulging of the wall. Solutions may involve improving drainage, reinforcing the wall, or rebuilding it entirely. In many cases, it's best to call a professional landscaping contractor to assess the issue and recommend the appropriate repairs.
Retaining walls are essential for controlling soil erosion and stabilizing slopes, but they require proper installation and ongoing maintenance to prevent problems like erosion. Trying to DIY a major retaining wall repair can be risky if you don't have the right expertise, so it's generally advisable to work with a qualified professional landscaper for anything beyond minor touch-ups.