Subject predicate When? Where? Why? How?
This sentence demonstrates how conjunctions such as and, but, and or are marked.
The earth's surface is constantly changing. Sometimes the changes are sudden. When Mt. St. Helens erupted in 1980, the mountain suddenly became 1300 feet shorter. The volcano spewed out smoke and ash. This ash fell on eastern Washington. It became part of the soil there.
Sudden changes also happened during some huge floods over 10,000 years ago. During the last ice age, the world was much colder. In a canyon in what is now northern Idaho, ice built up. The ice made a natural dam about half a mile high, blocking the Clark Fork River. The water from the river made a huge lake in Idaho and Montana. At last, when the water was about half a mile deep, the ice dam began to float. Then the dam broke into pieces.
The water suddenly rushed out from behind the dam. For several days the water and ice flowed through eastern Washington in a huge flood. In those few days the flood carried away topsoil, rocks, and huge boulders from the region now called the Channeled Scablands. The water eventually made its way to the Columbia River and to the Pacific Ocean.
After about a week, when the lake had drained completely, a new ice dam began to form. Because this happened many times, there were many floods before the last ice age ended. Each time an ice dam formed, water backed up as before until the dam finally broke again. The largest floods flowed with ten times as much water as now flows in all the rivers of the world!