Geology topics

Bruce Jaffe

Publications and source records attributed to Bruce Jaffe.

11 recordsLinked to original sources

USGS2018

Modeling morphodynamic development in the Alviso Slough system, South San Francisco Bay, California

Alviso Slough area, South San Francisco Bay, California, is the site of an ongoing effort to restore former salt production ponds to intertidal habitat. As restoration proceeds and the levees surrounding the former salt production ponds are breached, the increase in tidal prism and associated sediment scour in the sloughs will remobilize legacy mercury deposits. A numerical model that is able to assess patterns of sediment transport, erosion, and the fate of remobilized sediments can improve mercury remobilization estimates and inform management actions. The goals of the current research are to (1) validate a 2D geomorphic model for Alviso Slough using bathymetric surveys and to (2) apply the validated model for Alviso Slough to investigate scenarios of sea level rise and levee breaching on the long-term scour in Alviso Slough. The 2D geomorphic numerical model applies the Delft3D Flexible Mesh (software by Deltares) that describes detailed interaction between hydrodynamics, sediment transport, and geomorphic change on a high resolution mesh. The morphodynamic modeling exercise shows that observed erosion and sedimentation patterns can be reproduced with skill. The associated suspended sediment concentrations are more difficult to reproduce. The model reveals tide residual flow patterns that are difficult to measure. These residual flow and transport patterns are the result of subtle, tide residual transport trends so that their effect becomes visible in multi-year simulations. Scenario model simulations show possible, illustrative impacts of sea level rise and potential management interventions (additional levee breaches).

California↗

USGS2014

The search for geologic evidence of distant-source tsunamis using new field data in California

A statewide assessment for geological evidence of tsunamis, primarily from distant-source events, found tsunami deposits at several locations, though evidence was absent at most locations evaluated. Several historical distant-source tsunamis, including the 1946 Aleutian, 1960 Chile, and 1964 Alaska events, caused inundation along portions of the northern and central California coast. Recent numerical tsunami modeling results identify the eastern Aleutian Islands subduction zone as the “worstcase” distant-source region, with the potential for causing tsunami runups of 7–10 m in northern and central California and 3–4 m in southern California. These model results, along with a review of historical topographic maps and past geotechnical evaluations, guided site selection for tsunami deposit surveys. A reconnaissance of 20 coastal marshlands was performed through site visits and coring of shallow surface sediments to determine if evidence for past tsunamis existed. Although conclusive evidence of tsunami deposits was not found at most of the sites evaluated, geologic evidence consistent with tsunami inundation was found at two locations: Three marshes in the Crescent City area and Pillar Point marsh near Half Moon Bay. Potential tsunami deposits were also evaluated at the Carpinteria Salt Marsh Reserve in Santa Barbara County. In Crescent City, deposits were ascribed to tsunamis on the basis of stratigraphic architecture, particle size, and microfossil content, and they were further assigned to the 1964 Alaska and 1700 Cascadia tsunamis on the basis of dating by cesium-137 and radiocarbon methods, respectively. The 1946 tsunami sand deposit was clearly identified throughout Pillar Point marsh, and one to two other similar but highly discontinuous sand layers were present within 0.5 m of the surface. A tsunami-origin interpretation for sand layers at Carpinteria is merely consistent with graded bedding and unsupported by diatom or foraminiferal assemblages. Additional studies, including age dating, grain-size, and microfossil analyses are underway for the deposits at Crescent City, Pillar Point marsh, and Carpinteria, which may help further identify if other tsunami deposits exist at those sites. The absence of evidence for tsunamis at other sites examined should not preclude further work beyond the reconnaissance-level investigations at those locations.

California↗

USGS2011

New insights of tsunami hazard from the 2011 Tohoku-oki event

We report initial results from our recent field survey documenting the inundation and resultant deposits of the 2011 Tohoku-oki tsunami from Sendai Plain, Japan. The tsunami inundated up to 4.5 km inland but the > 0.5 cm-thick sand deposit extended only 2.8 km (62% of the inundation distance). The deposit however continued as a mud layer to the inundation limit. The mud deposit contained high concentrations of water-leachable chloride and we conclude that geochemical markers and microfossil data may prove to be useful in identifying the maximum inundation limit of paleotsunamis that could extend well beyond any preserved sand layer. Our newly acquired data on the 2011 event suggest that previous estimates of paleotsunamis (e.g. 869 AD Jōgan earthquake and tsunami) in this area have probably been underestimated. If the 2011 and 869 AD events are indeed comparable, the risk from these natural hazards in Japan is much greater than previously recognized.

Sendai Plain↗

USGS2010

Identification of tsunami deposits in the geologic record; developing criteria using recent tsunami deposits

There is a need for a clear procedure to identify tsunami deposits in the geologic record. Data from published studies documenting recent tsunami deposits provide a means of developing identification criteria based on the sedimentary characteristics of unequivocal tsunami deposits. Recent tsunami deposits have many sedimentary characteristics in common. All had sharp or erosional basal contacts. Sand was typically deposited in sheets that blanketed pre-existing topography and generally thinned landward. Deposit thickness was dependent on local topography; deposits were thicker in swales or local depressions and thinner on ridges or topographic highs. Deposits typically had 1-4 layers. Normal grading was common and often confined to individual layers. In muddy environments, sediments contained mud and soil rip-up clasts and mud often capped the deposits or layers. Boulders were often present, either isolated or scattered in groups. Sedimentary structures were rare, and included cross-bedding, laminations, scour and fill structures, and truncated flame structures. The composition, grain size, and surface texture of the grains reflected the coastal and nearshore source for the sediments. These sedimentary characteristics are the basis for developing site-specific tsunami deposit identification criteria that can be used in paleotsunami deposits investigations.

Open-File Report↗

USGS2006

A history of intertidal flat area in south San Francisco Bay, California: 1858 to 2005

A key question in salt pond restoration in South San Francisco Bay is whether sediment sinks created by opening ponds will result in the loss of intertidal flats. Analyses of a series of bathymetric surveys of South San Francisco Bay made from 1858 to 2005 reveal changes in intertidal flat area in both space and time that can be used to better understand the pre-restoration system. This analysis also documents baseline conditions of intertidal flats that may be altered by restoration efforts. From 1858 to 2005, intertidal flat area decreased by about 25% from 69.2 +6.4/-7.6 km2 to 51.2 +4.8/-5.8 km2. Intertidal flats in the north tended to decrease in area during the period of this study whereas those south of Dumbarton Bridge were either stable or increased in area. From 1983 to 2005, intertidal flats south of Dumbarton Bridge increased from 17.6 +1.7/-2.5 km2 to 24.2 +1.0/-1.8 km2. Intertidal flats along the east shore of the bay tended to be more erosional and decreased in area while those along the west shore of the bay did not significantly change in area. Loss of intertidal flats occurred intermittently along the eastern shore of the bay north of the Dumbarton Bridge. There was little or no loss from 1931 to 1956 and from 1983 to 2005. Predictions of future change in intertidal flat area that do not account for this spatial and temporal variability are not likely to be accurate. The causes of the spatial and temporal variability in intertidal flat area in South San Francisco Bay are not fully understood, but appear related to energy available to erode sediments, sediment redistribution from north to south in the bay, and sediment available to deposit on the flats. Improved understanding of sediment input to South San Francisco Bay, especially from Central Bay, how it is likely to change in the future, the redistribution of sediment within the bay, and ultimately its effect on intertidal flat area would aid in the management of restoration of South San Francisco Bay salt ponds.

California↗

USGS2006

Sediment deposition and erosion in south San Francisco Bay, California from 1956 to 2005

Sediment deposition and erosion in South San Francisco Bay from 1956 to 2005 was studied by comparing bathymetric surveys made in 1956, 1983, and 2005. From 1956 to 1983, the region was erosional. In contrast, from 1983 to 2005, the region was depositional. Analysis of subregions defined by depth, morphology and location revealed similarities in behavior during both the erosional and depositional periods. During the entire period of the study, there was net erosion in the shallows (<1 m depth) on the eastern shore of the bay north of the Dumbarton Bridge and net deposition in the region south of Dumbarton Bridge. The rates, however, reflected the sediment regime of each time period. Erosional areas were less erosional during the period with net deposition and depositional zones were more depositional. The cause for the increase in deposition from 1983 to 2005 is unknown, but could be related to an increase in sediment supply from Central Bay. The patterns of deposition and erosion and the change in rates are consistent with an increase in sediment supply from the north, as would occur if the supply from Central Bay increased from 1956-1983 to 1983-2005. Additional research is needed to fully understand why South San Francisco Bay became depositional from 1983 to 2005 and to determine the implications of this change to the planned salt pond restoration in the region.

Open-File Report↗

USGS2003

Tsunami

No abstract available.

Earthquake Spectra↗

USGS2003

Preliminary analysis of cores from north San Francisco Bay, California

During the mid-to late-1800's, large quantities of tailings from hydraulic gold mining in the Sierra Nevada were deposited in San Francisco Bay (Gilbert, 1917; Jaffe et al., 1998; Capiella et al., 1999). This rapid deposition also choked river systems and deposited mercury-contaminated sediments in the rivers and Bay. Hydraulic mining was stopped in 1884 by a California Supreme Court decision. Deposition in the Bay slowed in the late 1800's and early 1900's as a result of this decrease in sediment supply (Jaffe et al., 1998; Capiella et al., 1999). During the mid-1900's, sediment supply was further reduced by water works projects (dams, diversions, etc.), creating an erosional system in the study area by the late 1900's. The re-working of these sediments poses environmental and biological concerns regarding mercury in the bay. The location of these deposits is important for understanding the health of the bay waters. In March 2000, the U.S. Geological Survey collected sediment cores in the study area to determine the location of mercury-contaminated hydraulic mining debris. The study area (Figure 1) comprises 400 km2 and consists of San Pablo Bay and Suisun Bay, both of which are part of the San Francisco Bay estuary. Grizzly Bay, a subembayment of Suisun Bay, is also part of the study area. For the purpose of this report the term Suisun Bay will be used collectively for both areas. The present channel system in Suisun Bay is composed of three channels that flow through the bay. The primary channel runs in the southern section of Suisun Bay. A smaller channel flows between Roe Island and Ryer Island. The deepest channel flows through Suisun Cutoff, north of Ryer Island, and past Grizzly Bay. All three channels join at Carquinez Strait where they continue through the southern section of San Pablo Bay, and into San Francisco Bay. The average depths in San Pablo and Suisun Bays at mean sea level are 3.7 m and 5.8 m, respectively (Smith et al., 2002).

California↗

USGS2003

Cascadia Tsunami Deposit Database

The Cascadia Tsunami Deposit Database contains data on the location and sedimentological properties of tsunami deposits found along the Cascadia margin. Data have been compiled from 52 studies, documenting 59 sites from northern California to Vancouver Island, British Columbia that contain known or potential tsunami deposits. Bibliographical references are provided for all sites included in the database. Cascadia tsunami deposits are usually seen as anomalous sand layers in coastal marsh or lake sediments. The studies cited in the database use numerous criteria based on sedimentary characteristics to distinguish tsunami deposits from sand layers deposited by other processes, such as river flooding and storm surges. Several studies cited in the database contain evidence for more than one tsunami at a site. Data categories include age, thickness, layering, grainsize, and other sedimentological characteristics of Cascadia tsunami deposits. The database documents the variability observed in tsunami deposits found along the Cascadia margin.

British Columbia;California;Oregon;Washington↗

USGS1999

Sedimentation and bathymetry changes in Suisun Bay: 1867-1990

Understanding patterns of historical erosion and deposition in San Francisco Bay is crucial in managing such issues as locating deposits of sediment-associated contaminants, and the restoration of wetland areas. These problems were addressed by quantitatively examining historical hydrographic surveys. The data from five hydrographic surveys, made from 1867 to 1990, were analyzed using surface modeling software to determine long-term changes in the sediment system of Suisun Bay and surrounding areas. A surface grid displaying the bathymetry was created for each survey period, and the bathymetric change between survey periods was computed by differencing these grids. Patterns and volumes of erosion and deposition, sedimentation rates, and shoreline changes were derived from the resulting change grids. Approximately 115 million cubic meters of sediment were deposited in the Suisun Bay area from 1867 to 1887, the majority of which was debris from hydraulic gold mining in the Sierra Nevada. Just under two-thirds of the area of the study site was depositional during this time period, while less than one-third of it was erosional. However, over the entire study period, the Suisun Bay area lost sediment, indicating that a large amount of erosion occurred from1887 to 1990. In fact, this area lost sediment during each of the change periods between 1887 and 1990. Because erosion and deposition are processes that may vary over space and time, further analyses of more specific areas were done to examine spatial and temporal patterns. The change in the Suisun Bay area from being a largely depositional environment to an erosional one is the result of a combination of several factors. These factors include the regulation and subsequent cessation of hydraulic mining practices, and the increase in flood control and water distribution projects that have decreased sediment supply to the bay by reducing the frequency and duration of peak flow conditions. Another pattern shown by the changing bathymetry is the substantial decrease in the area of tidal flat (defined in this study as the area between mean lower low water and the shoreline), particularly in Grizzly Bay and Honker Bay. These tidal flats are important to the bay ecosystem, providing stability and biologic diversity.

California↗

USGS1998

Popular beach disappears underwater in huge coastal landslide — Sleeping Bear Dunes, Michigan

In February 1995, a 1,600-foot stretch of popular beach at Sleeping Bear Dunes National Lakeshore suddenly slid into the waters of northeastern Lake Michigan. The National Park Service (NPS) immediately requested the assistance of the U.S. Geological Survey (USGS) in evaluating the hazard at the lakeshore. To protect the public, USGS and NPS scientists are conducting studies that will help predict when the landslide-prone area will move again.

Michigan↗