Puget Sound
Puget Sound is a complex estuarine system of interconnected marine waterways and basins located on the northwest coast of the U.S. state of Washington. As a part of the Salish Sea, the sound has one major and two minor connections to the Strait of Juan de Fuca, which in turn connects to the open Pacific Ocean. The major connection is Admiralty Inlet; the minor connections are Deception Pass and the Swinomish Channel.
Puget Sound extends approximately from Deception Pass in the north to Olympia in the south. Its average depth is and its maximum depth, off Jefferson Point between Indianola and Kingston, is. The depth of the main basin, between the southern tip of Whidbey Island and Tacoma, is approximately.
In 2009, the term Salish Sea was established by the United States Board on Geographic Names as the collective waters of Puget Sound, the Strait of Juan de Fuca, and the Strait of Georgia. Sometimes the terms "Puget Sound" and "Puget Sound and adjacent waters" are used for not only Puget Sound proper but also for waters to the north, such as Bellingham Bay and the San Juan Islands region.
The term "Puget Sound" is used not just for the body of water but also the Puget Sound region centered on the sound. Major cities on the sound include Seattle, Tacoma, Olympia, and Everett. Puget Sound is also the second-largest estuary in the United States, after Chesapeake Bay in Maryland and Virginia.
Names
In 1792, George Vancouver gave the name "Puget's Sound" to the waters south of the Tacoma Narrows, in honor of Peter Puget, a Huguenot lieutenant accompanying him on the Vancouver Expedition. This name later came to be used for the waters north of Tacoma Narrows as well.An alternative term for Puget Sound, used by a number of Native Americans and environmental groups, is Whulge, an anglicization of the Lushootseed name for Puget Sound,, which literally means "sea, salt water, ocean, or sound". The name for the Lushootseed language,, is derived from the root word, an alternative name for Puget Sound.
Definitions
The USGS defines Puget Sound as all the waters south of three entrances from the Strait of Juan de Fuca. The main entrance at Admiralty Inlet is defined as a line between Point Wilson on the Olympic Peninsula, and Point Partridge on Whidbey Island. The second entrance is at Deception Pass along a line from West Point on Whidbey Island, to Deception Island, then to Rosario Head on Fidalgo Island. The third entrance is at the south end of the Swinomish Channel, which connects Skagit Bay and Padilla Bay. Under this definition, Puget Sound includes the waters of Hood Canal, Admiralty Inlet, Possession Sound, Saratoga Passage, and others. It does not include Bellingham Bay, Padilla Bay, the waters of the San Juan Islands or anything farther north.Another definition, given by NOAA, subdivides Puget Sound into five basins or regions. Four of these correspond to areas within the USGS definition, but the fifth, called "Northern Puget Sound" includes a large additional region. It is defined as bounded to the north by the international boundary with Canada, and to the west by a line running north from the mouth of the Sekiu River on the Olympic Peninsula. Under this definition, significant parts of the Strait of Juan de Fuca and the Strait of Georgia are included in Puget Sound, with the international boundary marking an abrupt and hydrologically arbitrary limit.
According to Arthur Kruckeberg, the term "Puget Sound" is sometimes used for waters north of Admiralty Inlet and Deception Pass, especially for areas along the north coast of Washington and the San Juan Islands, essentially equivalent to NOAA's "Northern Puget Sound" subdivision described above. Kruckeberg uses the term "Puget Sound and adjacent waters". Kruckeberg's 1991 text, however, does not reflect the 2009 decision of the United States Board on Geographic Names to use the term Salish Sea to refer to the greater maritime environment.
Geology
Continental ice sheets have repeatedly advanced and retreated from the Puget Sound region. The most recent glacial period, called the Fraser Glaciation, had three phases, or stades. During the third, or Vashon Glaciation, a lobe of the Cordilleran Ice Sheet, called the Puget Lobe, spread south about 15,000 years ago, covering the Puget Sound region with an ice sheet about thick near Seattle, and nearly at the present Canada-U.S. border. Since each new advance and retreat of ice erodes away much of the evidence of previous ice ages, the most recent Vashon phase has left the clearest imprint on the land. At its maximum extent the Vashon ice sheet extended south of Olympia to near Tenino, and covered the lowlands between the Olympic and Cascade mountain ranges. About 14,000 years ago the ice began to retreat. By 11,000 years ago it survived only north of the Canada–US border.The melting retreat of the Vashon Glaciation eroded the land, creating a drumlin field of hundreds of aligned drumlin hills. Lake Washington and Lake Sammamish, Hood Canal, and the main Puget Sound basin were altered by glacial forces. These glacial forces are not specifically "carving", as in cutting into the landscape via the mechanics of ice/glaciers, but rather eroding the landscape from melt water of the Vashon Glacier creating the drumlin field. As the ice retreated, vast amounts of glacial till were deposited throughout the Puget Sound region. The soils of the region, less than ten thousand years old, are still characterized as immature.
As the Vashon glacier receded a series of proglacial lakes formed, filling the main trough of Puget Sound and inundating the southern lowlands. Glacial Lake Russell was the first such large recessional lake. From the vicinity of Seattle in the north the lake extended south to the Black Hills, where it drained south into the Chehalis River. Sediments from Lake Russell form the blue-gray clay identified as the Lawton Clay. The second major recessional lake was Glacial Lake Bretz. It also drained to the Chehalis River until the, in the northeast Olympic Peninsula, melted, allowing the lake's water to rapidly drain north into the marine waters of the Strait of Juan de Fuca, which was rising as the ice sheet retreated.
As icebergs calved off the toe of the glacier, their embedded gravels and boulders were deposited in the chaotic mix of unsorted till geologists call glaciomarine drift. Many beaches about the Sound display glacial erratics, rendered more prominent than those in coastal woodland solely by their exposed position; submerged glacial erratics sometimes cause hazards to navigation. The sheer weight of glacial-age ice depressed the landforms, which experienced post-glacial rebound after the ice sheets had retreated. Because the rate of rebound was not synchronous with the post-ice age rise in sea levels, the bed of what is now Puget Sound filled alternately with fresh and with sea water. The upper level of the lake-sediment Lawton Clay now lies about above sea level.
File:Seattle seen from Ferry on Puget Sound.jpg|thumb|The Downtown Seattle skyline, seen from a state ferry on Elliott Bay
The Puget Sound system consists of four deep basins connected by shallower sills. The four basins are Hood Canal, west of the Kitsap Peninsula, Whidbey Basin, east of Whidbey Island, South Sound, south of the Tacoma Narrows, and the Main Basin, which is further subdivided into Admiralty Inlet and the Central Basin. Puget Sound's sills, a kind of submarine terminal moraine, separate the basins from one another, and Puget Sound from the Strait of Juan de Fuca. Three sills are particularly significant—the one at Admiralty Inlet which checks the flow of water between the Strait of Juan de Fuca and Puget Sound, the one at the entrance to Hood Canal, and the one at the Tacoma Narrows. Other sills that present less of a barrier include the ones at Blake Island, Agate Pass, Rich Passage, and Hammersley Inlet.
The depth of the basins is a result of the Sound being part of the Cascadia subduction zone, where the terranes accreted at the edge of the Juan de Fuca Plate are being subducted under the North American Plate. There has not been a major subduction zone earthquake here since the magnitude nine Cascadia earthquake; according to Japanese records, it occurred on January 26, 1700. Lesser Puget Sound earthquakes with shallow epicenters, caused by the fracturing of stressed oceanic rocks as they are subducted, still cause great damage. The Seattle Fault cuts across Puget Sound, crossing the southern tip of Bainbridge Island and under Elliott Bay. To the south, the existence of a second fault, the Tacoma Fault, has buckled the intervening strata in the Seattle Uplift.
Typical Puget Sound profiles of dense glacial till overlying permeable glacial outwash of gravels above an impermeable bed of silty clay may become unstable after periods of unusually wet weather and slump in landslides.
Hydrology
The United States Geological Survey defines Puget Sound as a bay with numerous channels and branches; more specifically, it is a fjord system of flooded glacial valleys. Puget Sound is part of a larger physiographic structure termed the Puget Trough, which is a physiographic section of the larger Pacific Border province, which in turn is part of the larger Pacific Mountain System.Puget Sound is a large salt water estuary, or system of many estuaries, fed by highly seasonal freshwater from the Olympic and Cascade Mountain watersheds. The mean annual river discharge into Puget Sound is, with a monthly average maximum of about and minimum of about. Puget Sound's shoreline is long, encompassing a water area of and a total volume of at mean high water. The average volume of water flowing in and out of Puget Sound during each tide is. The maximum tidal currents, in the range of 9 to 10 knots, occurs at Deception Pass. Water flow through Deception Pass is approximately equal to 2% of the total tidal exchange between Puget Sound and the Strait of Juan de Fuca.Image:Edward S. Curtis Collection People 047.jpg|thumb|left|Evening on Puget Sound by Edward S. Curtis, 1913
The size of Puget Sound's watershed is. "Northern Puget Sound" is frequently considered part of the Puget Sound watershed, which enlarges its size to. The USGS uses the name "Puget Sound" for its hydrologic unit subregion 1711, which includes areas draining to Puget Sound proper as well as the Strait of Juan de Fuca, the Strait of Georgia, and the Fraser River. Significant rivers that drain to "Northern Puget Sound" include the Nooksack, Dungeness, and Elwha Rivers. The Nooksack empties into Bellingham Bay, the Dungeness and Elwha into the Strait of Juan de Fuca. The Chilliwack River flows north to the Fraser River in Canada.
Tides in Puget Sound are of the mixed type with two high and two low tides each tidal day. These are called Higher High Water, Lower Low Water, Lower High Water, and Higher Low Water. The configuration of basins, sills, and interconnections cause the tidal range to increase within Puget Sound. The difference in height between the Higher High Water and the Lower Low Water averages about at Port Townsend on Admiralty Inlet, but increases to about at Olympia, the southern end of Puget Sound.
Puget Sound is generally accepted as the start of the Inside Passage.