FLOOD02685 - Laserfiche WebLink

Home Browse Search

:l< c.F. Way'homas. R.D. JarrttlI Geomorplw/ogy /1 (/994) 15-40 A 8 30 8ASAlICE 30 MELT-oUTTIU ~ .""" n.7.$ "" FlB.PIroXlMAL. FlB. DISTAL z w 0 z .. .. 7S w ~ . ~ . w ,: Z SO 0 10 10 Q z w ~ z . 25 z . , , . 30 SEDIMENT A..OW 30 . 2OAOf08Cl . .. ...... ~ n..t2S0 IO' z w 0 z .. " 7S . ~ . 0 . Z ,: w z SO 0 10 " Q z w ~ z . 25 . .~. , , , . " .. .. eo " .. " .. , 20.0&080 , .. ..".. DlP AHGl.E, IN OEGREES DIP ANGLE,IN DEGREES DIP ANGLE, IN DEGRU:S ..... . ~.'. '..;": ..,.:,;,,:,.- ~~'.:":"...:,....:t_~~~ , t, . ~ ;; ; : Fig. 11 p the A....lo: I' Fronl l:,n~ Fig:. 10. Frequency histograms of imbrication angles of c)ags from (A) glacigenic: mass-now depositS (modified from DowdesweU and Sharp, 1986). and (B) debris.flow depositS in the Scottish Highlands (modified from Innes. 1986). RB. is right bank. LB. is left bank. proximal is proximal to channel. distal is distal from channel. N is number of samples. skew"! these ,Ie comparison. Data from Table 4 are plotted as a ratio plot of normalized eigenvalues (Fig. 9). The relation implied by Fig. 10 is not suitable for prediction (via regression analysis) because theX-Yvariables indicate a spurious relation (Chayes. 1949, /971) and consid- erable scatter. However. the plot illustrates some dis- tinct differences in deposit clast fabric that may be related to the processes that formed the deposits. Clasts in fluvial deposits that form in high-energy environ- ments tend to have a high degree of preferred orienta- tion (Rust. 1972; Kauffman and Ritter. 1981). Eigenvalue ratios associated with these deposits will plot in the upper left corner of Fig. 9. Clasts in debris- flow and. hyperconcentrated-flow deposits show less preferred orientation. Eigenvalue ratios from those deposits should plot in the middle to lower right pan of Fig. 9. In nature. it is likely that a continuum of eigenvalue ratios is possible and that this is controlled by the hydrodynamic propenies and composition of the sediment-Buid mixture. Thus, other criteria (see e.g. Costa. 1988), in addition to clast fabric data, must be used to identify the depositional process of bouldery deposits in upland catchments like Arthurs Rock Gulch. The data shown in Fig. 9 indicate that debris-Bow and hyperconcentrated-flow(?) deposits have In SII .1'2 values that are < l.I. and In .1'21 S3 values> 0.7. In contrast. water-flood deposits have In Sll .1'2 values that 5.7.1'.'" range from 0.95 to 1.8 and In .1'21 S3 values that range from about 0.2 to 0.8. Eigenvalues derived from fabric measurements on FB 3 deposi ts at Site 5 and FB 2 depos- its at Site 4 plot in or near the domain of hyperconcen- trated-flow(?) and debris-flow deposits. indicating that these deposits may not have formed by flash flooding. Other Colorado Front Range flash-flood deposits from Tucker Gulch near Golden. Colorado and Turkey Creek near Morrison. Colorado. also have clast fabrics and associated eigenvalues that are more like hyper- concentrated-Bow(?) and debris. Bow deposits than water-flood deposits (Fig. 9). These deposits require further study before their specific origin can be ade- quately evaluated. Another component of the clast fabric that may be useful for differentiating debris-Bow from flash-flood deposits is the dip, or imbrication angle of the clast A- B plane. Frequency histograms of imbrication angles from debris-flow and glacigenic mass-wasting deposits (sediment-Bows. ice-slope colluvium; Fig. 10) aretyp- ically unimodal and negatively skewed (modal class about 15~20'). The frequency distribution of imbri- cation angles associated with flash-flood deposits. in contras~ is unimodal and symmetric (modal class about 50-55'; Fig. II). The frequency distribution of imbrication angles associated with the FB3 deposit at Site 5 and the FB2 deposit at Site 4 are negatively We u: tribu[i~\ll and sl,"" tive~~\~' of radiI.... mate lh, fluvi~I'r BCC~HI and FIll been dCI' The~l.h' FBli"" aharal'h'l age in l \ FBO,:Uh! its forllH 1973. to FBO. III" extren\l' mate Hu~ BP (/vi'" 1984) ,lI may h:I\' firess"'" ders WIll and Sl",1 weathl'!.