Answer: Water erosion
A scientist observes the ocean tides moving large amounts of sand away from the beach is a evidence for natural process which is known as water erosion. Water erosion is a process of removal or detachment of upper soil layers from its's original place due to the effect of water. The rate of erosion may be rapid or slow depending upon the soil, the landscape and weather conditions. The beach exhibit sandy soil whose particles are not connected or aggregated with each other and not with the surface over which it is present. Therefore, sand being loose soil is taken away by oceanic tides due to water erosion.