The geology of the margin Accreted along the Cascadia subduction zone contain high concentrations of organic matter, which is converted to methane. Where does the organic material come from?

Organic material formed from photosynthesis and other biological activity settles on the sea floor. This material trapped within the thrust complexes within the formed accretionary wedge. Faulting possibly associated with methane emissions

faults

The image above is from McNeill et al (1997) and right image is EM300 swath bathymetry from the WA margin in 2007; showing faults that appear to be associated with methane emission sites on the WA shelf.

McNeill, L.C., K.A. Piper, C. Goldfinger, L.D. Kulm, and R.S. Yeats (1997). Listric normal faulting on the Cascadia continental margin. J. Geophys. Res. 102 (B6): 12,123-12,138. 125° 00' W 124° 00' W 123° 00' W

Vancouver Island Flattening and truncation of the margin sediments during low sea Strait of Juan de Fuca Washington stands during glacial periods has

Juan de Fuca Canyon exposed the folded 48° 00' N

. Hoh layers. Head

Hoh River PACIFIC 3

100 50 Queets 150 River Mid-shelf mud deposit Raft River

Quinault Quinault Canyon River SCALE 1:500,000 Point 1 inch represents 7.89 miles Grenville

10 0 10 Kilometers Moclips 0 10 10 River Miles Projection - UTM 10 Copalis Datum - NAD83 150 River Grays 50 Harbor

47° 00' N

Grays Canyon 10

Willapa OCEAN Bay Guide Canyon

Thickness of Mid-Shelf Holocene Mud Layer (m) Willapa Canyon

rock outcrop

0 - 5

5 - 10 Columbia River 10 - 20 Astoria Canyon 20 - 30

30 - 40 Oregon

46° 00' N

Tillamook Head

9 Nittrouer estimate of sediment 100 50 thickness in meters 150 200

Bathymetric contour (interval = 10 m)

Tillamook Bay

125° 00' W 124° 00' W 123° 00' W Figure 1. Isopach map of the Mid-Shelf Silt Deposit compiled from pre-existing USGS seismic survey data. Bathymetry contours generated by Michael R. Hamer from NOS hydrographic soundings obtained from NOAA

48° 00' N

Site of Interest in relation to the Olympic Marine Sanctuary

Olympic Marine Sanctuary

Grays Canyon reef and methane plume site