Most geologic events happened very slowly. Name two geologic events- one land building and one erosional- that happen fast enough for people to see.
Volcanoes may serve as land building events. The Hawaiian islands were formed as lava from volcanoes from deep under the ocean's surface erupted and the magma cooled and increased the height of the volcanic cone. Lava from the Kilauea volcano is currently adding to the surface area of the island of Hawai'i. Surtsey Island rose above water level of the North Atlantic Ocean on Nov. 15, 1963 and continued to grow until June 5, 1967.
In the aftermath of earthquakes under the ocean, tsunamis may cause extensive erosional damage along shorelines. Scientists who compared the coastline of some of the Kuril Islands, first surveyed and measured in 2006 and revisited after tsunamis in Nov., 2006 and Jan., 2007, found that "in some places the amount of sand and soil removed by tsunami erosion was nearly 50 times greater than the amount deposited."