Sea stacks represent erosional remnants following sea cliff retreat. Marine terraces, such as those of Palos Verdes, are indications of uplift or lowering of sea level. The greater the angle of waves to shore, the greater the amount of longshore current. Sand accumulated on the north side of a groin indicates that the direction of longshore drift is from the north. Sea cliff retreat occurs by the combined forces of wave erosion and mass wasting.
Plastic is the most abundant solid waste product washed up on beaches.
Although common in the past, incineration is no longer considered a viable alternative to elimination of solid waste. The Fresh Kills landfill forms the highest hill on the east coast from Boston to Florida. A sewer plant that utilizes secondary forms of treatment yields a potable effluent. High nitrogen and phosphorus in streams leads to a bloom of algae which eventually decay robbing the ecosystem of oxygen. Hot springs are example of the hydrothermal environment.