Guam has a tropical marine environment, the weather is generally warm and humid; not like our unpredictable Oregon weather! However, an average of 3 tropical storms and one typhoon will pass within 180 nautical miles of Guam each year! This is a scary thing living on a remote island, but the people have taken precautions by building all their houses out of concrete. A wooden house would be unheard of, Can you imagine?!
The terrain has a volcanic origin, just like all islands, and it is surrounded by coral reefs. Guam straddles the edge of the Philippine Plate with the Pacific Plate thrusting below it -- an area called the subduction zone. The Mariana islands are volcanic products of the magma released at this subduction zone. The melting of rock produces magma containing alot of water at the subduction zone. When this magma reaches the surface, the water expands very rapidly, which is why island-arc volcanoes are so explosive. According to National Geographic, it is the water and sulfur that give these volcanoes their bang.
There is also a relatively flat coralline plateau that is the main source for much of the freshwater consumed by the islanders. Some of th Guam coastlines have been described as similar to that of the Oregon Coast; steep rocky cliffs, with a magnificent ocean below it.
[Click on the map of the volcano chain if you want to see it a bit bigger]
