Science Plan: Details

This page contains some documents that were draft science plans. Below is the science plan that was scoped for the current LCC funded phase of this project. Other phases of the project, as they become funded, will get updated science plans. The draft science plans are at the bottom of this page.

Project Title: Tectonic land level changes and their contribution to sea level rise, Humboldt Bay region, Northern California

    Project Summary

  • This project will evaluate and quantify the two primary factors driving observed sea level changes in Northern California: eustatic sea level rise (ESLR) and tectonic land level changes. Local sea level changes will be mapped by incorporating land and sea level observations through deployment of temporary tide gages (at historic locations previously observed) and analysis of existing historic (1931-198Smilie: 8) level line surveys. The new sea level observations (6-9 months) will facilitate development of a 34-year trend (1978–2012) in sea level change in the vicinity of Humboldt Bay, as well as provide information about potential tectonic land level changes that will be verified through analysis of the land-based level surveys. Trends in land and sea level change in north coastal California determined from this study, when integrated with the work of Dr. Ray Weldon and colleagues at University of Oregon, fills an important data gap regarding coastal uplift and subsidence in the southern Cascadia subduction zone. In addition to helping complete the coastal uplift & subsidence distribution along the Cascadia margin, the results of this study will provide necessary baseline information that can be used by land managers and planners in northern California to anticipate and plan for changes in sea level over the next century. Because ongoing land-level changes exceed ESLR in some locations, determining these spatial and temporal trends are crucial to determining the local sea-level trends in northern California.
  • Background and Need

  • Recent advancements in the understanding of global environmental change have motivated coastal communities and land managers to better understand and initiate planning for future sea- level rise. Sea-level rise poses threats to local infrastructure, as well as species and ecosystems dependent on occupying a specific elevation range relative to sea-level. Reasonable estimates of future sea level change, although increasingly necessary to inform land and resource management in the coastal zone, are lacking in the Humboldt Bay region.
  • Vertical land changes must be considered when estimating local sea level changes and the potential effects at any given location. Local sea level is the combined measured effects of eustatic sea level change and vertical land movement, which can either amplify or reduce the observed rate of sea level change. Active tectonic processes associated along the Pacific margin from northern California to Vancouver Island cause ongoing vertical land level change, which can be observed along the coast in both the geologic record as well as in ongoing modern day deformation (Mitchell et al., 1994; Nelson et al., 1996; Atwater and Hemphill-Haley, 1997; Fluck et al., 1997; Burgette et al., 2009). Tectonically-driven vertical land level changes in the Humboldt Bay region are within the same order of magnitude as ESLR. Therefore, both variables are critical in examining local sea level changes over typical planning horizons.
  • Humboldt Bay is at the southern end of the Cascadia subduction zone where the offshore oceanic plate is descending below the onshore continental plate. The land and seafloor within this interface is subject to continuous vertical land- level changes throughout the seismic cycle, which can be characterized by examining both the long term strain accumulation and short term energy release. The earth’s crust flexes vertically on a time scale of hundreds of years as strain accumulates during interseismic time intervals. The resulting energy release during an earthquake typically results in land movement in the opposite sense of motion to the observed interseismic vertical land level changes. This seismogenic process repeats itself on a time scale of hundreds of years. Modern analogues of this tectonic phenomena have been well documented over the last half century in Alaska in 1964 (Plafker, 1969), Chile in 1960 (Atwater, 1992), and Northern California (Carver, 1992). More recently this phenomena has been observed in Japan after the 2011 Tohoku earthquake. Observing the slow steady interseismic vertical motion will not only allow a refinement of local sea level change, but provide a basis for estimating future coseismic land level change.
  • Near Humboldt Bay, published uplift rates range from approximately –2.5 mm/yr to 3 mm/yr (Verdonck 2006; Leonard et al. 2004). Deformation of the offshore Gorda plate at the Mendocino triple junction may complicate contemporary efforts to accurately model interseismic land level changes in this region (Leonard et al. 2004) in the absence of additional tidal gaging data. Repeated marsh burial provides strong evidence of coseismic subsidence and therefore, inferred interseismic uplift (Vick, 1988 and Patton, 2004) at Humboldt Bay, which appears to be at odds with the limited tidal gaging records available from the North Spit. Preliminary inference from existing instrumentation (i.e., continuous GPS observations and tide gauges) suggest that the Humboldt Bay region experiences -3 to -1 mm/yr of vertical land level change, resulting in observed sea level change of 5.3 to 3.3 mm/yr from south to north (HBVRSWG, 2011). These estimates were derived by combining 30 years of sea level data with 5 years of continuous GPS measurements. Land subsidence is in the opposite direction of sea level rise and contributes to accelerated rates of apparent sea level rise. The rate of vertical land level change transitions from subsidence to uplift along California’s north coast between Trinidad and Crescent City. These rates are greater than in other parts of the Pacific Northwest and California (HBVRSWG, 2011).
  • Coastal land managers have a need to understand how estuarine wetland ecosystems, adjacent freshwater wetlands, and the animal communities that depend upon these habitats will redistribute themselves in response to sea-level change. In the Humboldt Bay region, salt marsh and eelgrass habitats that support diverse assemblages of migratory waterfowl and shorebirds, as well as fish and invertebrates, occupy narrow elevation ranges (1.7 to 2.6 m and -1.7 to 0.5 m relative to mean lower low water, respectively (Eicher 1987; Gilkerson 200Smilie: 8) making them especially vulnerable to changes in sea-level. Historic modification of coastal wetlands as a result of railroad and levee construction has reduced the area currently capable of supporting salt marsh by 90 % in Humboldt Bay (Pickart 2001) which in turn, limits the extent to which these species can migrate landward in response to rising sea-level, absent significant changes in land management and conservation. Remaining salt marsh habitats in Humboldt Bay and the Eel River delta have also been degraded by the introduction and spread of invasive species, most notably, Spartina densiflora (Pickart 2001). Freshwater emergent wetlands adjacent to salt marsh in the Humboldt Bay and Eel River Delta also support large numbers of migratory waterfowl and may be impacted by saltwater intrusion associated with rising sea-level.
  • Potential management responses with respect to protecting coastal wetland habitats threatened by rising sea level are limited by a number of factors, the most significant of which include availability of funding and suitable upland area for purchase to effect restoration and conservation. All of these factors conspire to make managing coastal wetlands in the face of climate change and specifically sea level rise a challenging endeavor.
  • By deploying a network of tide gauges around Humboldt Bay, we will substantially refine our understanding of the local and regional variations in rate of sea level rise or fall. Land managers will have valuable information by which they can better estimate the trajectory of specific wetland areas with respect to conversion to other habitat types. In addition to understanding near-term vulnerability of existing wetlands to local sea-level change, managers will also gain a better understanding of the potential for specific adjacent upland areas to provide future habitat refuge for coastal wetland species of interest.
  • Observing and quantifying sea-level change is fundamental to making sound management decisions in the coastal areas of Northern California and has been identified by groups including: the Humboldt Bay Initiative workgroup, the California Department of Fish and Game, the California Department of Transportation, and local and regional planning departments. This project will address the first logical step in characterizing the tectonic land-level changes that influence sea-level inundation in the Humboldt Bay region.
  • Objective

  • This project will characterize the interseismic tectonic land-level change associated with the southern Cascadia subduction zone. Understanding this ongoing phenomenon will allow us to quantify and predict future sea-level trends in northern California. Results from this study will provide fundamental sea- level rise data for making sound management decisions as they apply to managing coastal landscapes and the species and ecosystems that inhabit them, particularly those within the tidal prism, which are the most vulnerable to future sea-level rise . Quantifying future local sea-level change is the first logical step in planning management strategies for coastal ecosystems.
  • Methods

  • A combination of near shore water-level and onshore land-level surveys will be utilized to determine the tectonic land level changes and sea level trends around Humboldt Bay.
    • Temporary Tide Gage Deployment

    • When the North Spit tide gage was constructed, there were 11 locations within Humboldt Bay and its estuaries where sea-level was observed from 1978-1980. We propose to deploy a minimum of 3, and up to 6, temporary tide gages at historic locations for a period of 6-9 months. Tide gages and bar-code levels will be provided by Dr. Ray Weldon of University of Oregon. Site infrastructure (stilling well, staff plate, power system) will be constructed and each site will be surveyed to their respective tidal bench mark. Contemporary (2011-2012) water-level observations will be compared to initial (1978-1980) observations to determine a 34 year sea-level trend at each location around Humboldt Bay. Of the 11 potential locations to reobserve sea-level, we have identified 3 locations as priority: 1) Hookton Slough in South Humboldt Bay, 2) Eureka, and, 3) Mad River Slough in North Arcata Bay. These locations provide broad geographic coverage within Humboldt Bay and have relatively robust initial historic records. In Addition, the US Army Corps of Engineers San Francisco District office (Anne Strum) has agreed to provide 2010 tide gaging data from 2 locations in Humboldt Bay (Fields landing and Samoa), providing 2 more data points to include in the analysis.
    • In Trinidad, approximately 10 miles North of Humboldt Bay, there is a robust 10 year historic record from
      1977-1987. The Trinidad Pier is getting rebuilt in 2011-2012, and will be observed if site construction allows. We are contacting the Trinidad Rancheria regarding funding opportunities for a permanent tide gage on the new pier to support this and other projects. Additionally, the BLM plans to support funding through the BLM King Range Conservation District to establish sea-level trends near recreational routes in the King Range for public access and trail planning purposes. A new observation point may be established near Shelter Cove or other location along the King Range.
    • Level Surveys

    • Numerous historic level surveys have been completed around Humboldt Bay. There are 7 projects involving ~70 control points that were leveled in the vicinity of Humboldt Bay from 1931-1992 (http://www.ngs.noaa.gov). Forty (40) survey marks have 2 observations between 1944-1967 or 1967-1988, and 19 have 3 observations from 1944-1988. University of Oregon will provide bar code leveling equipment to perform short level ties between historic surveys where possible to provide new measurements for meaningful locations only observed once (eg. 1931, 1944). All historic surveys will be tied to the North Spit tide gage (where needed) for proper reference to mean sea level, which will be the surface all observation points will be referenced to. Analyzing the repeated surveys will determine secular trends as well as evaluate monument stability or instability through time. We are communicating with CalTrans Dist. 1 regarding potential for survey work to be performed by their own staff to re-level the NAVD88 level line, last observed 23 years ago. A new survey would extend the historic record 20+ years and provide new baseline information to evaluate future earthquake induced land-level changes along critical infrastructure.
    • Continuous GPS stations operated by EarthScope (http://earthscope.org) exist just beyond the North and South shorelines of Humboldt Bay and provide excellent anchor reference points for future potential GPS survey work. Both the County of Humboldt Surveys Office and the National Geodetic Survey have indicated they have the capacity to provide GPS equipment for projects such as a Height Modernization Survey (2-4cm vertical accuracy), which would help provide a mechanism to efficiently and effectively monitor land changes into the future.
    • Education and Outreach

    • Planned outreach activities include direct interaction with Humboldt State University and University of Oregon Geology programs, regular project updates will be provided to the local ecosystem science & planning community through the Humboldt Bay Initiative working group meetings, briefings to the Humboldt County Public Works and Planning Departments, the HSU Geology colloquium seminars which are open to the public, the Harbor District’s Humboldt Bay Symposium, and presentations to the Humboldt Friends of Geology (HFOG) semi-annual meetings. A student and/or a senior team member may present the results at a scientific conference such the Geological Society of America or American Geophysical Union annual meeting. Presenting emerging results from this study will hopefully spark interest from the many stake holders that have an interest in estimating future sea-level change in northern California and the regional observation points can be densified or expanded in the future.
    • Technical Advisory

    • While all team members are considered technical advisory to the project, and the project team has many years experience in tide gaging and leveling work, technical consultation and project planning will also be presented for review to Don Campbell, CalTrans Dist. 1 Surveys and Right-of-Way Support, and Marti Ikehara, the National Geodetic Survey’s Advisor to the State of California. These individuals have no official presence in the working group but have been enthusiastic project proponents as well as valuable technical advisory.

    Geographic Extent

  • All of the proposed project will take place in Humboldt County, California. The proposed tide gage installations may range from Shelter Cove in the south to Trinidad Harbor to the north, with the bulk of the observations occurring within Humboldt Bay. This distribution of observation points will allow us to evaluate regional sea-level trends to compare to the interior of Humboldt Bay. Completion of this project will fill in the last remaining portion of the Cascadia subduction zone that hasn’t been characterized in this fashion, allowing for refinement of earthquake hazard assessments for the region.
  • References Cited

    • Atwater, B., Nelson, A.R., Clague, J.L., Carver, G.A., Yamaguchi, D.K., Bobrowsky, P.T., Bourgeois, J., Darienzo, M.E., Grant, W.C., Hemphill-Hailey, E., Kelsey, H.M., Jacoby, G., Nishenko, S., Palmer, S., Peterson, C. D., and Reinhart, M.A., (1995) Coastal geologic evidence for past great earthquakes at the Cascadia subduction zone, Earthquake spectra, vol. 11: 1-18.
    • Atwater, B.F., and Hemphill-Haley, E., (1997), Recurrence intervals for great earthquakes of the past 3,500 years at northeastern Willapa Bay, Washington: U.S. Geological
      Survey Professional Paper 1576, 108 p.
    • Burgette, R.J., Weldon II, R.J., and Schmitt D.A., Interseismic uplift rates for western Oregon and along strike variation in locking on the Cascadia subduction zone. Journal of Geophysical research, 114, B01408, doi:10.1029/2008JB005679
    • Carver G.A., and Burke, R.M., (1992), Late Cenozoic Deformation on the Cascadia subduction zone in the region of the Mendocino triple junction. Pacific Cell, Friends of the Pleistocene guidebook for the field trip to northern coastal California.
    • Eicher, A.L. 1987. Salt marsh vascular plant distribution in relation to tidal elevation, Humboldt Bay, California. M.A. thesis. Humboldt State University. Arcata, California, USA. 83 pp.
    • Fluck, P., R.D. Hyndman, andK.Wang (1997), Three-dimensional dislocation model for great earthquakes of the Cascadia subduction zone, J. Geophys. Res., 102(B9), 20,539–20,550, doi:10.1029/97JB01642.
    • Gilkerson, W. 2008. A spatial model of eelgrass (Zostera marina) habitat in Humboldt Bay, California. MS Thesis. Humboldt
      State University, Arcata, California.
    • Mitchell, C. E., P. Vincent, R. J.Weldon, and M. A. Richards (1994), Present day vertical deformation of the Cascadia margin, Pacific Northwest, United States, J. Geophys. Res., 99(B6), 12,257–12,277, doi:10.1029/94JB00279.
    • Nelson, A.R., Shennan, I., and Long, A.J., (1996), Identifying coseismic subsidence in tidal-wetland stratigraphic sequences at the Cascadia subduction zone of western
      North America: Journal of Geophysical Research, v. 101, p. 6115–6135.
    • Patton, J.R. 2004. Late Holocene Coseismic Subsidence and coincident tsunamis, Southern Cascadia Subduction Zone, Hookton Slough, Wigi, (Humboldt Bay), California: M.S. Thesis, Arcata, California, Humboldt State University, 85p.
    • Pickart A.J. 2001 The distribution of Spartina densiflora and two rare salt marsh plants in Humboldt Bay 1998 -1999. Unpublished document, U.S. Fish and Wildlife Service, Arcata, California.
    • Plafker, G., (1969), Tectonics of the March 27, 1964 Alaska earthquake: U.S. Geological Survey Professional Paper 543-I, 74 p.
    • Leonard, L J, Hyndman, R D, and Mazzotti, S. 2004. Coseismic subsidence in the 1700 great Cascadia earthquake: Coastal estimates versus elastic dislocation models. Geological Society of America Bulletin. Vol. 116, no. 5-6, pp. 655-670.
    • Verdonck, D, 2006: Contemporary vertical crustal deformationin Cascadia. Technophysics Vol.417: pp. 221–230.
    • Vick, G. 1988. Late Holocene Paleoseismicity and relative vertical crustal movements, Mad River Slough, Humboldt Bay, California: M.S. Thesis, Arcata, California, Humboldt State University, 88 p.

Draft and Submitted Science Plans

  • Draft Plan presented at the first meeting in October, 2010. (docx pdf)
  • Notes from initial meeting in October, 2010. (doc pdf)
  • Map of potential control sites (jpg pdf)
  • Revised Science plan following review of notes from initial meeting in October, 2010. (doc pdf)
  • Proposal submitted to the USFWS for funding from the LCC. This is the basis for the Science Plan outlined above. (docx pdf)
  • Reports and Updated submitted to USFWS. These reports and summaries include observations and results from our analyses outlined in the science plan.

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