Location.--Latitude 46°16'35", Longitude
122°09'41", in NE 1/4 NE 1/4 Section 10, Township 9 North,
Range 5 East, in Skamania County, Hydrologic Unit 17080005,
Mount St. Helens National Volcanic Monument, at entrance of Spirit Lake
Outlet Tunnel, 5.6 miles north-northeast of Mount St. Helens volcanic
edifice, and at river mile
undetermined. Drainage
area is 18.0 mi2, at entrance to Spirit Lake Outlet
Tunnel. Prior to the volcanic eruption on May 18, 1980, 14.9
mi2. Datum of
gage is 3,400 feet above NGVD of 1929, data published to NGVD of
1929.
Lake elevation varies from
minimum recorded elevation of 3,437.00 feet on October 28, 1997 to
maximum recorded elevation of 3,460.13 feet on February 5,
1997.
An
additional sensor has been installed and reflects the lake
elevation at the intake gate.
Upper tunnel sensor values less 3,400 feet
indicate no flow through tunnel structure.
This station managed by the Cascades Volcano Observatory (Vancouver).