Late Quaternary Variations in the Level of Paleo-Lake Malheur, Eastern Oregon

1998 ◽  
Vol 50 (3) ◽  
pp. 276-282 ◽  
Author(s):  
Daniel P. Dugas
Keyword(s):  
Late Quaternary ◽  
Threshold Elevation ◽  
Lake System ◽  
The Pacific ◽  
Dry Conditions ◽  
Terminal Pleistocene ◽  
The Pacific Ocean ◽  
Lake Floor ◽  
Low Levels ◽  
Barrier Beaches

The highest shoreline features of paleo-Lake Malheur are undated gravelly barrier beaches south of Harney Lake that lie ca. 3.5 m higher than the hydrographic outlet of Harney Basin at Malheur Gap (1254 m). The earliest Quaternary record for Lake Malheur consists of occurrences of water-deposited tephra dated to ca. 70,000–80,000 yr ago. The next identified lake interval is dated by shells with ages of ca. 32,000 and 29,500 yr B.P. No dates are available for the terminal-Pleistocene Lake Malheur. Lake(s) were present between ca. 9600 and 7400 yr B.P., although periodic low levels or desiccation are suggested by a paleosol dated as ca. 8000 yr B.P. The lake system probably dried further after 7400 yr B.P., although dates are lacking for the period between ca. 7400 and 5000 yr B.P. Dune deposits on the lake floor are ca. 5000 yr old and indicate generally dry conditions. Fluctuating shallow lakes have probably characterized the last 2000 years. A date of 1000 yr B.P. gives a maximum age for beach deposits at 1254 m, near the basin threshold elevation. Thus, the Malheur Lake system may have drained to the Pacific Ocean by way of Malheur Gap during the latest Holocene.

scholarly journals Spatial Patterns of Preinstrumental Moisture Variability in the Southern Canadian Cordillera

2005 ◽  
Vol 18 (15) ◽  
pp. 2847-2863 ◽  
Author(s):  
Emma Watson ◽  
Brian H. Luckman
Keyword(s):  
Twentieth Century ◽  
Severity Index ◽  
Drought Severity ◽  
Canadian Cordillera ◽  
Entire Area ◽  
The Pacific ◽  
Dry Conditions ◽  
The Pacific Ocean ◽  
Instrumental Records ◽  
Precipitation Records

Abstract Extreme wet and dry intervals of the last 350 yr in the Canadian Cordillera and adjacent United States are examined using a network of 25 tree-ring-based precipitation and Palmer Drought Severity Index (PDSI) reconstructions. Reconstructed twentieth-century-mapped patterns compare well with patterns based on the instrumental records at both annual and decadal scales. During the most extreme events, dry conditions occurred over the entire area. The longest widespread drought in the last 350 yr occurred from 1917 to 1941. Shorter intervals of more severely dry conditions occurred in the early 1720s, 1750s, 1790s, 1860s–70s, and the 1890s. Many of the driest individual years and most extreme dry periods of <7 yr are reconstructed for the eighteenth century. The longest, wettest periods identified by these reconstructions occurred in the early twentieth century. In agreement with published studies that explore links between instrumental precipitation records from the region and conditions in the Pacific Ocean, the reconstructed records show that drier (wetter)-than-normal conditions are associated with El Niño (La Niña) events and the positive (negative) phase of the Pacific decadal oscillation (PDO).

Late Quaternary sedimentology and geochronology of small playas on the Southern High Plains, Texas and New Mexico, U.S.A.

2008 ◽  
Vol 70 (1) ◽  
pp. 11-25 ◽  
Author(s):  
Vance T. Holliday ◽  
James H. Mayer ◽  
Glen G. Fredlund
Keyword(s):  
New Mexico ◽  
Late Quaternary ◽  
High Plains ◽  
Southern High Plains ◽  
The Holocene ◽  
Eolian Dust ◽  
C Isotopes ◽  
Eolian Sand ◽  
Dry Conditions ◽  
Terminal Pleistocene

AbstractPlayas are small, circular basins forming a ubiquitous component of the southern High Plains landscape. They are filled with carbonaceous mud deposited since the terminal Pleistocene. The stratigraphy and geochronology of 30 playas was investigated to better understand the paleoenvironmental record of basin filling. At the base of the fill in some playas is a well sorted eolian sand dated between ~ 13,000 and ~ 11,000 14C yr BP. The beginning of mud deposition, representing aggradation of eolian dust on a moist, vegetated playa floor was largely between ~ 12,000 and ~ 10,500 14C yr BP. Playa filling slowed ~ 9000 to ~ 4000 14C yr BP, probably due to dry conditions, increased ~ 4000 to ~ 2000 14C yr BP, then slowed again. Eolian sand and loam, likely representing regional aridity, accumulated in some basins episodically just prior to ~ 10,700 14C yr BP, between ~ 8600 and ~ 4700 14C yr BP, and at ~ 1300 14C yr BP. Stable C isotopes from one basin indicate that the playa was inundated only seasonally throughout the record beginning ~ 11,500 14C yr BP. The phytolith record in that basin indicates an abrupt shift toward cooling ~ 11,400 to ~ 11,200 14C yr BP and then increasing importance of xeric-adapted C4 grasses through the Holocene.

On the Pacific Ocean regime shift

2001 ◽  
Vol 28 (19) ◽  
pp. 3721-3724
Author(s):  
Cathy Stephens
Keyword(s):  
Pacific Ocean ◽  
Regime Shift ◽  
The Pacific ◽  
The Pacific Ocean
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