Liquefaction at Finley Quarry, WA?

Two reports by two different teams of geologists describe the same outcrop, sediments, and structural features at Finley Quarry near Pasco, WA (Coppersmith et al., 2014; Sherrod et al., 2016). Why there were two teams, who knows? On most things, everyone agreed. Opinions differed regarding liquefaction.

I'm not going to lie, publication of the Sherrod article raised an eyebrow. My spidey sense began tingling with their unit descriptions and the tingle only intensified when I reached their interpretations. Upon completion, I reached for my own field notes and I emailed three short questions to the lead author, a federal civil service employee with an office at the University of Washington. Receiving no response from Mr. Sherrod, I contacted a more senior geologist at USGS to ask if he might deliver my questions. He did, but again, no response. That doesn't happen very often.

Now any mention of liquefaction in Washington gets my attention and Finley Quarry is my stomping ground. I have visited the site several times and have spent many hours investigating the local geology surrounding it. And I'm not alone. In fact, many geologists have published papers on the quarry and its surroundings (Laval, 1956; Jones and Deacon, 1966; Jahns, 1967; Brown, 1968; Bingham et al., 1970; Jones and Landon, 1978 + Appendix; Rockwell, 1979; Farooqui, 1977; Farooqui and Thoms, 1980; Kienle/Foundation Sciences, 1980; Reidel et al., 2021).

The most conspicuous features there are the breccia-filled fractures that lace the basalt high wall of the quarry. Similar steep, rubble- and sediment-filled fractures are present in other basalt quarries around the region (Horse Heaven Hills, Frenchman Hills, Rattlesnake Hills, etc.), but the ones at Finley are particularly cool. They were correctly interpreted decades ago in a report by Bingham et al. (1970),

The large "clastic dikes" in the Finley Quarry reported by Jones and Deacon (1966, Plate 13, photograph 5), Jahns (1967, Fig. 11), and R.E. Brown (1968, p. 26) are not Touchet-age clastic dikes, but instead are older sedimentary fillings of joints and fissures that opened up as the blocks tipped slightly northward, probably toward an unsupported fault scarp. The sediments that have filled them appear to be well weathered and stained and cemented with caliche, suggesting that the material is part of the Ringold Formation, and that the fault movement began in Ringold time or earlier.

But Sherrod wasn't talking about the rubble-filled fractures. He was talking about dike- and sill-like "liquefaction" features enclosed by "loess" which he had attributed to seismic shaking.

Oblique aerial photo of Finley Quarry from Google Earth. View to the east.

My field sketch of the basic geology at Finley Quarry, made from the sagebrush slope across the road. The area of concern lies at the far left.

Photo by Jones and Landon (1978, Fig. 14) captioned "Finley Quarry-The Butte: Caliche-cemented fault breccia". The old photo lacks detail, but shows a large, intact outcrop with a good thickness of undisturbed sediment remaining.

Rubble-filled cracks in the basalt high wall at Finley Quarry. There is no offset associated with these fractures. They are joints associated with the incipient topple of large blocks toward the river. According to U-series work on the cemented rubble by Paces (2014), the last movement on faults at Finley Quarry was during the middle Pleistocene, "Carbonate‐rich gouge present along the fault exposed at Finley quarry shows complex layering and cementation paralleling the attitude of the fault...ages range from 700 +270/‐160 ka to 224 ±36 ka...These ages are consistent with repeated faulting over a several hundred thousand year time frame in the middle Pleistocene. If younger fracturing and cementation events are present (for instance, the event that formed the colluvial fault wedge dated at 17 ka), they were not sampled in this block of gouge."

Nearly identical rubble-filled fractures are known in other basalt quarries, like this one near the crest of the Frenchman Hills anticline.

Another example of a large, steeply-dipping, sediment-filled fracture in basalt on the south flank of Rattlesnake Hills.

But the Sherrod team had it wrong. They misinterpreted both the "liquefaction" feature (Unit 19) and the nature of the enclosing sediments (Units 13 and 16). The feature is a branching, ,Pleistocene-age Touchet-type clastic dike and the enclosing sediment is a silty Missoula flood deposit - a silt-pebble diamict, not loess. The dike is deformed, which is not unusual in colluvial settings such as this. Its fine grained fill makes it a bit more ambiguous, but deciphering its origin poses no big challenge to folks familiar with these dikes. The dike is certainly older than Holocene as it does not cut the modern soil (Holocene Humic-stained L1 loess). Evidence of Holocene liquefaction is nonexistent in Eastern Washington despite the region's copious amount of unconsolidated sediment lying in close proximity to mapped Quaternary faults. If the feature at Finley Quarry was produced by liquefaction, similar features should be found nearly everywhere in the region. The Sherrod team was overenthusiastic in attributing a single ambiguous feature to earthquake-caused liquefaction. Angster seems to have made a similar mistake in his own trench across the river (Angster et al., 2023), though the features there look nothing like the features here.

Finley Quarry trench log (Sherrod et al., 2016, Fig. 9).

Detail of Unit 19, the "liquefaction" feature. Units 13 and 16 are silty flood deposits, not loess. Unit 19 is a Touchet-type clastic dike intruding flood sediments, like hundreds of thousands of other such dikes in the region. The sketch implies the feature cuts Unit 17 (a Holocene loess). If Unit 17 is in fact Holocene-age loess, then the crosscutting interpretation is dubious. If its L1 loess, which is Pleistocene unit, then its fine.

Geologists in the 1980s noted unfaulted post-flood colluvium and loess overlying older faulted materials at Finley Quarry, but found no evidence of liquefaction (Foundation Sciences, 1980, Figure 4). Considerable bedrock has been removed from the quarry in the intervening decades, which means investigators probably observed somewhat different exposures.

Others agree with me. Pertinent comments in a table buried near the end of the Coppersmith report (Coppersmith et al., 2014, Table 7.2) suggest there were disagreements in the field,

The postulated liquefaction feature (dike and sill d) that appears to post-date the deposition of [~11,000 year old Glacier Peak G] tephra is the strongest evidence for a strong shaking earthquake in the general vicinity of Finley quarry (which may or may not be on the RAW-Rattles fault source). The best expressed part of the mapped feature cross cuts Unit 13. The USGS log interprets Unit 13 as L1 loess. However, this unit shares characteristics similar to massive to poorly bedded slackwater deposits observed elsewhere (e.g., at the MCBONEs locality) (i.e., it contains scattered clasts and irregular blocks of pre-flood ice-rafted or ripped up material). Although the mapped extent of the feature up into the modern soil suggests a post-flooding event, additional work or review is needed to preclude a flood-related liquefaction phenomenon.

Liquefaction is pushed pretty hard by the Sherrod team, which is concerning given the huge effort geologists at the Hanford Site and the hydroelectric dams have made over the past 80 years to locate some evidence of it. To date, no liquefaction has been observed in more than a dozen trenches excavated across young scarps in the Yakima Fold Belt. This includes trenches opened by USGS, Washington Geological Survey, and DOGAMI at Ahtanum Ridge (Bennett et al., 2016), Boylston Mountains (Barnett et al., 2013), Toppenish Ridge (Campbell and Repasky, 1995), Wenas Valley (Sherrod et al., 2013), Smyrna Bench (Bingham et al., 1970), Walla Walla (Farooqui and Thoms, 1980), Lind Coulee (West and Shaffer, 1988), Gable Mountain (Bingham et al., 1970), Spencer Canyon (Sherrod et al., 2015), Wallula (Angster et al., 2023), Kittitas Valley (Huddleston, 2022), Gate Creek (Bennet et al., 2021), and Gales Creek (Horst et al., 2021). Likewise, I am unaware of any reports - or even rumors - of Holocene liquefaction in young sediments east of the Cascade divide.

The Finley Quarry site is a highly disturbed exposure and a far cry from anything resembling a type section for surficial units, much less a classic liquefaction locality. Sherrod et al. (2016) smacks of ambition. Its a Seattle-based team, bent on making a new discovery in some remote canyon that finds themselves struggling to comprehend the local geology. I wonder why the team didn't instead focus their efforts on the huge roadcuts that beautifully expose the same strata just 5 minutes west of Finley Quarry. The cuts along Hwy 397 are continuous over a hundred meters and are twenty meters high. They are safe and hikeable with large pullouts to accommodate vehicles. There, dozens of sheeted Pleistocene-age clastic dikes cut a spectacular section. None are liquefaction features.

Large, accessible exposures along Hwy 397 just west of Finley Quarry display all of the important units and relationships. If you come to Finley Quarry, you should come here too. These cuts will provide context, a wider perspective, and will help sort out tricky stratigraphic and structural relationships. The outcrop lies right on the Wallula Fault Zone.

Pro tip: When doing field geology in a place you don't know well, ask a field geologist to check your work. Better yet, invite one to join you at the outcrop. We will save you a lot of time. Here's a hasty sketch of the strata exposed in Hwy 397 roadcut that I made while on the phone with someone named Kara. I think she was from the government and en route to the Finley area to check out the geology.

Refs

Bingham et al., 1970, Geologic investigation of faulting in the Hanford region, Washington with a section on the occurrence of microearthquakes, U.S. Atomic Energy Commission, Division of Reactor Development and Technology Report No. 90-27, 126 pgs.

Camp et al., 2017, Field-Trip Guide to the vents, dikes, stratigraphy, and structure of the Columbia River Basalt Group, eastern Oregon and southeastern Washington, USGS/DOI Scientific Investigations Report 2017–5022–N, p. 65-66

Cooley, S.W., 2020, Sheeted clastic dikes in the megaflood region, MT-WA-OR-ID, Northwest Geology (Tobacco Root Geological Society), v. 49

Coppersmith et al., 2014, Appendix E: Structural analysis and Quaternary investigations in support of the Hanford PSHA in Hanford Sitewide Probabilistic Seismic Hazard Analysis, Pacific Northwest National Lab Report No. 23361

Foundation Sciences, Inc., 1980, Geologic reconnaissance of parts of the Walla Walla and Pullman, Washington, and Pendleton, Oregon 1 degree x 2 degree AMS quadrangles, a consultant's report to U.S. Army Corps of Engineers-Seattle District, Contract DACW67-80-C-0125, 144 pgs.

Jenkins, O.P., 1925, Clastic dikes of eastern Washington and their geologic significance, American Journal of Science, 5th Series, v. 10

Paces, J.B., 2014, 230Th/U ages supporting Hanford site-wide Probabilistic Seismic Hazard Analysis, AMEC/PNNL/USDOE Office of Environmental Management/USGS Report, 28 pgs.

Sherrod et al., 2016, Active Faulting on the Wallula Fault within the Olympic-Wallowa Lineament, Washington State, USA, Geological Society of America Bulletin v. 128