- The document discusses the impacts of basaltic lava flows on the Owyhee River in Oregon, including morphological, hydrological, ecological, and regional landscape effects. - When lava flows entered the river canyon, it disrupted normal fluvial processes, blocking and diverting the river, forming lava dams and lakes. This thwarted the river's erosion and lowered the landscape more slowly. - Examples from the Owyhee River include the Saddle Butte and West Crater lava dams that formed lakes and deposited thick lacustrine sediments, demonstrating the long-term hydrological changes caused by intra-canyon volcanism.

1. IMPACTS OF BASALTIC VOLCANISM ON INCISED FLUVIAL SYSTEMS DOES THE RIVER GIVE A DAM? Kyle House, Nevada Bureau of Mines and Geology Cooper Brossy, Fugro /WLA, Inc. Liz Safran, Lewis & Clark College Lisa Ely, Central Washington University Jim O’Connor, U.S. Geological Survey Owyhee River Interstate Geological Investigation Network

2. Goal of this talk Describe the characteristics of the response of the Owyhee River, OR to the incursion of voluminous basaltic lava flows. Thanks to input from NinadBondre Kathy Cashman Duane Champion Ryan Crow Natalia Deligne Cassie Fenton Nick Foit Gordon Grant Chris Henry Keith Howard Karl Karlstrom Caitlin Orem Shannon Othus Tabitha Prosser Terry Spell Brent Turrin

3. ‘When lava met valley’ Intracanyon lavas create extreme disruption of ‘normal’ fluvial processes Geomorphic effects Hydrological effects / Ecological effects Regional landscape effects

4. ‘When lava met valley’ Morphological effects Channel and valley re-paving River diversion / realignment Channel Blockage and damming

5. Intracanyon flows: ‘When lava met valley’ Hydrological effects / Ecological effects Hey, there’s a lake! What the…there’s no sediment! Uh-oh, the new dam is leaking! !

6. ‘When lava met valley’ Regional effects Master stream forced to cut lava for 10ks of years ‘Normal’ vertical and lateral erosion thwarted Huge rock and sediment pulse to manage Deceleration of landscape lowering

7. The Owyhee River Tributary to the Snake River Junction of Nevada, Oregon, and Idaho Drainage area 8600 sq. miles Bulk of watershed on volcanic plateau Miocene rhyolite lavas Dispersed lacustrine basins Mio-Pliocene plateau basalt Pliocene river canyon Plio-Pleistocene intra-canyon basalt flows (6-8) Idaho Oregon Nevada

8. Middle Owyhee River: Quaternary lava flows Many late Cenozoic flows on the plateau, but only 6 extensive and well-preserved Quaternary intracanyon flows at surface Greeley lava Qbg: .78 to 1.8 Ma Coffee Pot Qbcp < 7 ka Bogus Rim Qbr: 1.8 Ma Clarks Butte Qbc: 240 ka Rocky Butte Qbrb: 30 ka Saddle Butte Qbs:145 ka West Crater Qbw: 60 ka 10 km

9. Re-Paving courtesy of Bogus Lavas

10. The Bogus Lava paleovalley: upstream view

11. Intracanyon lava flow stratigraphy: flow margins

12. Middle Owyhee River: Quaternary lava dams 6 principal intacanyon lava flows 5 extant lava dams / deltas Greeley Bar Qbg: .78 to 1.8 Ma Iron Point Qbcp < 7 ka Ryegrass Qbr: 1.8 Ma Sand Spring Qbc: 240 ka Granite Ck Qbrb: 30 ka Qbw: 60 ka Qbs:145 ka 10 km

13. Saddle Butte Lava Dam

14. Hello, water? It’s me…lava! Passage zone Subaerial lava 40 m Lava delta ‘foresets’ Saddle Butte lava-water interaction features

15. Saddle Butte lava dam Subaerial lava Lava delta Dam Forebay Fluvio-lacustrine sediments landslide Earlier advance

16. Greeley Bar lava dam Greeley lava flow and lava delta Bogus Rim lava

17. West Crater Lava Dam

18. West Crater lava dam stratigraphy West Crater lava delta Fossil tributary Paleovalley divide Saddle Butte lava

19. West Crater lava delta and fossil tributary

20. Lava dam models: Crow et al., 2008

21. Type section of lava dam failure? Mile 192, Colorado River in Grand Canyon

22. Grand Canyon lava dam failure deposit

23. Grand Canyon lava dam failure deposit

24. Lava dam models: Crow et al., 2008 Owyhee lava dams

25. Spillway gravels on Bogus Lavas

26. Bogus Rim lava spillway gravels human

27. Spillway Gravels, West Crater lava Yep, that’s a fault

28. 1400 sq. km

29. West Crater lava dam lake seds Saddle Butte lava West Crater lava dam (60-80 ka) 47 ka 55 ka 25 m of lacustrine sediments with Cascadian tephra layers. Evidence for long-lived lake

30. Why does the river give a dam?

31. The gift that keeps on giving:The lava-landslide link Lava flows in the Owyhee lead to landslides River diversion Undercutting Lateral Unloading Landslide-rebound Stratigraphic loading

32. West Crater Lava Margin FAIL

34. Undercutting

35. ‘Rebound’

36. Lava UnloadingSediments Valley wall landslide Intracanyon Lava flow undercutting displacement unloading Lava margin landslide The Lava-Landslide Link

37. Owyhee landslide dam breach

38. Fluvial Incision History: river scale Cooper Brossy figure

39. Fluvial incision chronometers 1.8 Ma 1146 m 240 ka 972 m 70 ka 930 m 915 m

40. Lava Flow profiles: Reach-scale Meters Meters

41. The Bogus Lava background rate 80 m 220 m

42. Long term incision rate from Bogus Rim lava 270m in 1.8 Ma 0.15 mm /yr

43. Incision Rates at Dogleg Bend T5 Spillway 38.13 ka 50 T4 34.95 ka Meters above river surface 40 30 1 mm/yr 20 T3 T2 14.77 ka 11.1 ka 10 T3 T4 T5 T2

44. Thwarted Erosion That which may have transpired in absence of intracanyon lava flows What is the tangible influence of extrafluvial processes? What isn’t in the landscape because of this? From Hamblin, 1994