Coastal erosion at the mouth of the Ma River in Thanh Hoa, Vietnam is a big problem. Building hard structures to protect the coast makes it worse because we don't fully understand why erosion is happening. By looking at satellite images from 1987 to 2023, we found that the shape of the river mouth has changed a lot over the years. The river brings about 350,000 cubic meters of sand every year, with most of it going to the northern beach. This uneven sand distribution is causing the delta to move in different directions, leading to severe erosion. The sand moves along the shore at a rate of 90 square meters per day. This study helps us understand how cuspate deltas change over time, especially when we don't have a lot of field data.