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Richard J. Janda

Publications and source records attributed to Richard J. Janda.

7 recordsLinked to original sources
USGS1983

Influence of climate on progressive hillslope failure in Redwood Creek Valley, northwestern California

Both creep and earthflow processes control hillslope erosion over large parts of the Redwood Creek basin. The type of process and displacement rates are largely dependent on underlying bedrock type and precipitation input. Progressive creep with rates ranging from 1.0 to 2.5 mm/a dominates on slopes west of the Grogen fault underlain by sheared and foliated schists. Movement appears to respond primarily to annual increments of precipitation. Complex earthflows occur predominantly on slopes east of the Grogen fault underlain by sheared graywacke and mudstone. Movement rates range from 3.0 to 131.0 mm/a and characteristically display dominant rainy season movement.

Open-File Report↗
USGS1978

Mass movement and storms in the drainage basin of Redwood Creek, Humboldt County, California — A progress report

Numerous active landslides are clearly significant contributors to high sediment loads in the Redwood Creek basin. Field and aerial-photograph inspections indicate that large mass-movement features, such as earthflows and massive streamside debris slides, occur primarily in terrain underlain by unmetamorphosed or slightly metamorphosed sedimentary rocks. These features cannot account for stream sediment derived from schist. Observed lithologic heterogeneity of stream sediment therefore suggests that large-scale mass movement is only one part of a complex suite of processes supplying sediment to streams in this basin. Other significant sediment contributors include various forms of fluvial erosion and small-scale discrete mass failures, particularly on oversteepened hillslopes adjacent to perennial streams. Photo-interpretive studies of landslide and timber-harvest history adjacent to Redwood Creek, together with analysis of regional precipitation and runoff records for six flood-producing storms between 1953 and 1975, indicate that loci and times of significant streamside landsliding are influenced by both local storm intensity and streamside logging. Analysis of rainfall records and historic accounts indicates that the individual storms comprising a late-19th-century series of storms in northwestern California were similar in magnitude and spacing to those of the past 25 years. The recent storms apparently initiated more streamside landslides than comparable earlier storms, which occurred prior to extensive road construction and timber harvest. Field observations and repeated surveys of stake arrays at 10 sites in the basin indicate that earthflows are especially active during prolonged periods of moderate rainfall; but that during brief intense storms, fluvial processes are the dominant erosion mechanism. Stake movement occurs mostly during wet winter months. Spring and summer movement was detected at some moist streamside sites. Surveys of stake arrays in two recently logged areas did not indicate exceptionally rapid rates of movement in three years following timber harvest.

California↗
USGS1971

An evaluation of procedures used in computing chemical denudation rates

Computations of chemical denudation rates (that is, the average rate of lowering of the earth's crust by chemical processes) should be based only upon those components of dissolved loads of streams that are derived from chemical weathering of rocks and soils, even though identification of those components is difficult and imprecise. Past computations of chemical denudation rates exaggerated by 1.4 to 2.4 times the significance of this process because they were calculated from total dissolved loads. Identification of separate denudation and nondenudation components in a water analysis can be done most readily for streams in crystalline silicate rock terrane where commonly 25 to 55 percent of the dissolved solids are HCO 3 −1 , SO 4 −2 , Cl −1 , and NO 3 −1 that cannot be derived from the underlying rock; instead these ions are derived either directly from the atmosphere or from atmosphere-biosphere interactions. Most of the remaining solutes are derived from chemical weathering or rainfall, or both. Existing data are often insufficient to separate these two components, but atmospheric contributions to dissolved loads of dilute natural waters are substantial. The commonly observed increased concentration of dissolved solids in chemically polluted rivers is produced by concentration of natural dissolved loads by evaporation, and by addition of solutes not present in natural waters. Concentration of natural solutes represents a modification of natural denudation processes that does not change the rate of denudation. Addition of new solutes represents man-induced, accelerated chemical denudation. Extrapolation of modern chemical denudation rates to geologic situations is extremely imprecise because of uncertainties in assessing man's influence on present dissolved loads, in reconstructing the number and magnitude of past climatic changes, and in evaluating the effects of evolving flora and fauna.

Bulletin of the Geological Society of America↗