Ocean AreasOregon ocean areas stretch approximately 360 miles from the mouth of the Columbia River to the California border and extend some 14 to 40 miles into the ocean.

The state's ocean jurisdiction [the Territorial Sea] extends three nautical miles from shore [Mean Low Water], although offshore rocks and islands can extend this area seaward, such as at Orford Reef near Cape Blanco.

o.cean (o'shen) n. 1. The entire body of salt water that covers approx. 72% of the earth's surface. 2. A great amount or expanse.

(Webster's New College Dictionary, 1995) 

About Ocean Areas in Oregon

Oregon ocean areas stretch approximately 360 miles from the mouth of the Columbia River to the California border and extend some 14 to 40 miles into the ocean.

The state's ocean jurisdiction [the Territorial Sea] extends three nautical miles from shore [Mean Low Water], although offshore rocks and islands can extend this area seaward, such as at Orford Reef near Cape Blanco.

Oregon's interests in ocean resource policy and management are not limited to state waters. Because the ocean is a fluid, dynamic environment and is part of a much larger regional marine ecosystem, ocean uses and activities that occur in federal waters farther to the west, such as fishing or, potentially, oil or gas drilling, can affect Oregon's coastal environment and communities.

So, Oregon has designated an Ocean Stewardship Area that extends from shore seaward across the relatively shallow continental shelf then down to the toe of the continental slope at about 2500 to 3000 meters deep, some 15 to 40 miles offshore. This area is the most biologically productive, where human uses and effects are most intense, and where the need for management and protection is greatest. The Ocean Stewardship Area was first expressed as a recommended policy in the Oregon Ocean Resources Management Plan, adopted in 1990, and was incorporated into Statewide Planning Goal 19, Ocean Resources, in 2000.

Features of Oregon's Continental Margin Oregon's continental margin is composed of three major features: the continental shelf, the continental slope, and the submarine canyons dissecting both.

Continental Shelf

Oregon's continental shelf is a relatively flat, gently sloping terrace. It is narrow in comparison with worldwide averages and ranges from about 17 kilometers (10 miles) off Cape Blanco to 74 kilometers (46 miles) off the central coast. In general, the shelf is steepest where it is most narrow. The depth of the shelf varies but is usually taken to be 200 meters, at which point the shelf merges with the steeper continental slope.

The shelf has several prominent, rocky, submarine banks of varying size. Four major banks create locally shallow areas amidst the otherwise deeper water of the shelf: Nehalem Bank, Stonewall Bank, Heceta Bank, and Coquille Bank. The rock blocks which form these banks have been uplifted by the underthrusting process at the base of the continental slope.

Rocky outcrops, erosional remnants of shoreward rock formations, are also found on the inner shelf, especially between Coos Bay and the Rogue River. Nearshore, sea stacks and other rocky islands provide nesting sites for sea birds. Many of these features are part of the Oregon Islands National Wildlife Refuge system.

Continental Slope

Like the continental shelf, Oregon's continental slope is also relatively narrow, from 20 kilometers (12 miles) at Cape Blanco to 96 kilometers (60 miles) off the Columbia River. Here the ocean floor drops rapidly to meet the Cascadia Basin some 2,000 meters below.

The upper slope is characterized by gently sloping benches and low-relief hills. Blocks of rocky material, probably hard mudstone , have been rapidly uplifted by the underthrusting oceanic plate and the building of an accretionary wedge at the bottom of the slope. Sediments have ponded behind these blocks to form the Cascade Bench off the north coast and the Klamath Bench off the south coast and northern California. The lower slope below 2,000 meters is quite steep and intersects the deep-sea bed of the Cascadia Basin at 2,200 meters off the north coast and 3,000 meters off the central and south coast.

Submarine Canyons

The outer edge of the continental shelf and continental slope is breached by two prominent submarine canyons and numerous smaller ones. The Astoria Canyon cuts into the outer shelf about 16 kilometers (10 miles) west of the Columbia River. During periods of lowered sea level, the Columbia and Rogue Rivers drained across what is now the continental shelf. The Astoria Fan, a large depositional feature on the eastern Cascadia Basin, lies at the base of the canyon. The Rogue Canyon is much smaller than the Astoria Canyon. It begins near the edge of the shelf offshore of the Rogue River and feeds directly down the continental slope onto the deep ocean floor.


This text abridged from The Oregon Ocean Book and other materials provided by Bob Bailey, OCMP
 

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