Oregon

Oregon (ⁱ/ˈɔːrᵻɡən/ AWR-ə-gən) is a state in the Pacific Northwest region of the United States. Oregon is bordered on the west by the Pacific Ocean, on the north by Washington, on the south by California, on the east by Idaho, and on the southeast by Nevada. The Columbia River delineates much of Oregon's northern boundary, and the Snake River delineates much of the eastern boundary. The parallel 42° north delineates the southern boundary with California and Nevada. It is one of only three states of the contiguous United States to have a coastline on the Pacific Ocean, and the proximity to the ocean heavily influences the state's mild winter climate, despite the latitude.

Oregon was inhabited by many indigenous tribes before Western traders, explorers, and settlers arrived. An autonomous government was formed in the Oregon Country in 1843, the Oregon Territory was created in 1848, and Oregon became the 33rd state on February 14, 1859. Today, at 98,000 square miles, Oregon is the ninth largest and, with a population of 4 million, 26th most populous U.S. state. The capital of Oregon is Salem, the second most populous of its cities, with 160,614 residents (2013 estimate). With 609,456 residents (2013 estimate), Portland is the largest city in Oregon and ranks 29th in the U.S. Its metro population of 2,314,554 (2013 estimate) is 24th. The Willamette Valley in western Oregon is the state's most densely populated area, home to eight of the ten most populous cities.

Crater lake

A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite, or in an artificial explosion caused by humans. Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not made. Crater lakes covering active (fumarolic) volcanic vents are sometimes known as volcanic lakes, and the water within them is often acidic, saturated with volcanic gases, and cloudy with a strong greenish color. For example, the crater lake of Kawah Ijen in Indonesia has a pH of under 0.5. Lakes located in dormant or extinct volcanoes tend to have fresh water, and the water clarity in such lakes can be exceptional due to the lack of inflowing streams and sediment.

Formation

Volcanic crater lakes

Crater lakes form as the created depression, within the crater rim, is filled by water. The water may come from precipitation, groundwater circulation (often hydrothermal fluids in the case of volcanic craters) or melted ice. Its level rises until an equilibrium is reached between the rates of incoming and outgoing water. Sources of water loss singly or together may include evaporation, subsurface seepage, and, in places, surface leakage or overflow when the lake level reaches the lowest point on its rim. At such a saddle location, the upper portion of the lake is contained only by its adjacent natural volcanic dam; continued leakage through or surface outflow across the dam can erode its included material, thus lowering lake level until a new equilibrium of water flow, erosion, and rock resistance is established. If the volcanic dam portion erodes rapidly or fails catastrophically, the occurrence produces a breakout or outburst flood. With changes in environmental conditions over time, the occurrence of such floods is common to all natural dam types.