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<br />
<br />COSTA AND JARRETT-DEBRIS FLOWS
<br />
<br />
<br />Figure 7. Old photo showing debris-flow lobe following 1914
<br />debris now on Cornet Creek at Telluride. Colo., area 7 in Figure
<br />2. (Courtesy of San Miguel Historical Society.)
<br />
<br />Small vegetation on debris fans is capable of di-
<br />verting debris flows transporting very coarse boul.
<br />ders without being scarred. Figure 8 shows a small
<br />tree, 80 mm (3 in) in diameter, that diverted a flow
<br />transporting boulders with diameters as large as 1,2
<br />m (4 ft) across the debris fan of Skyrocket Gulch
<br />near Ouray, Colo. An unscarred base of a willow
<br />with a diameter of 30 mm (1,2 in) on a small tribu-
<br />tary to South Halfmoon Creek near Leadville.
<br />Colo" that was engulfed by the lobe of a debris flow
<br />is shown in Figure 9,
<br />Because waterfloods are fully turbulent, the
<br />coarse sediment they carry badly scars or destroys
<br />any vegetation in the flow path on an alluvial fan at
<br />the mouth of the stream, Yet, as Figures 8 and 9
<br />
<br />315
<br />
<br />
<br />Figure 8. Small tree that diverted a recent debris flow across
<br />debris fan of Skyrocket Gulch near Ouray. Colo.. area 6 on
<br />Figure 2. Largest houlders moved had diameters as much as 1.2
<br />meters (4 ft).
<br />
<br />show, debris floods do not necessarily scar or de-
<br />stroy vegetation.
<br />[n 1977 the office of Midcontinent Coal Compa.
<br />ny, situated beside a tributary to South Fork Dutch
<br />Creek. upstream from Redstone, Colo., was buried
<br />by debris; damages were $500,000, A bus in the
<br />parking lot behind the building was moved more
<br />than 30 m (100 ft). The bus had no major structural
<br />damage and was not even tipped over, yet the flow
<br />at this point was transporting boulders with diam.
<br />eters as much as 2 m (6.5 ftj, Along the East River
<br />tributary near Crested Butte, Colo.. trees engulfed
<br />by levees had rocks with diameters as large as 0,5
<br />m (1.6 ft) packed around them. However, little bark
<br />on the trees was cut or marred, indicating low ve-
<br />
<br />Table 2. Trask Sorrblf:[ coefficient.I' for .WJ/JIl' dehri,\ (mild) flows alld fl'atajfood.\", TnJ.\k ,wrti"x ("(Jcjjicif.:'nt = ",.,Id:!:;: J'5 "" Ihird
<br />quartile, "2., = fir\'1 quarlill'.
<br />
<br /> Number
<br /> of
<br />Deposits and Locality Age Samples Range Average Source
<br /> Debris (mud) flows
<br />Fresno County, Calif Recent 50 5,0-25 9.7 Bull, 1964
<br />Wright wood, Calif 1941 10 2,7-5,0 ),9 Sharp and Nobles, 1953
<br />Rio Reventado, Costa Rica 1964 10 2.6-7.0 4,6 Waldron, 1967
<br />Trout Lake, Wash Recent 3 5.8-11.0 7,7 Jones, 1959 (in Waldron, 1967)
<br />Mount Rainier, Wash 5,700 years 41 9.0-1".4 1l.5 Crandell, 1971
<br />Mount S1. Helens, Wash 2,000 years " 4.9-10,2 7,8 Millineaux and Crandell, 1%2
<br />Mount S1. Helens. Wash 1980 3 6-19 12.3 Fink and others. 1981
<br />South Halfmoon Creek tributary, Colo 1977'.' 2 9.4-9.8 9,6 This report
<br /> Watcrlloods
<br />Fresno County. Calif Recent 3" 1.1-4,8 1.8 Bull,I%4
<br />Rubicon River, Calif 1964 31 1.5-3.4 1.9 Scott and Gravlee, 1%8
<br />Coffee Creek, Calif 1%4 9 1.4-4,9 "'!..7 Stewart and LaMarche, 1%7
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