The Ore Bin - Oregon Department of Geology and Mineral Industries

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Recent Erosion In 1972-73 the existing houses at Siletz Spit had been present for less than 10 years, and there had been no prior development. Little was known concerning the spit's erosional history. In 1970-71 erosion did occur along a 670-meter section of foredunes at the south end of the spit and a small stretch at the northern part of the developed section. Riprap placement prevented appreciable foredune losses, and no houses were seriously threatened. The maximum dune bluff recession, 15 meters, occurred in an unprotected park area. No strong storms developed during the mi Id winter of 1971-72. Erosion was minor except in the park area, where the foredune retreated another 20 meters. The severest episode of erosion occurred during the winter of 1972-73. One partially built home was destroyed (Figure 2), and others had to be protected by ri prap on three sides (Figures 3 and 4). The worst erosion took place along a 650-meter stretch of the central spit, opposite the artificial lagoons cut into the bay side of the spit. Figure 5 diagrams the erosion to the base of the foredunes, the maximum recession amounting to 30 meters in a 3-week period. Individual homeowners placed riprap in front of their properties, but unprotected vacant lots continued to erode. Flank erosion in the empty lots made it necessary to protect the sides of houses so that the group of three houses ended on a promontory supported by riprap (Figures 3, 4, and 5). Due to a disagreement between the developer, who owned the lots, and the individual leaseholders as to who should pay for the placement of the riprap, erosion to the empty lots was allowed to proceed until it threatened the road, at which time riprap was finally installed. The dispute is presently being settled in court. Long Term E rosi 0 n Erosion of the dunes of the spit exposed numerous drift logs, many of which had been sawed (Figure 6). This indicates that spit development was contemporaneous with logging along the Oregon Coast. The influx of settlers and logging started about 1895. Sawed logs within the spit indicate that the portion on which the houses had been built suffered previous erosion some time after 1895. The dunes must have then built back out, incorporating sawed logs in the process, and become re-established. A detai led qualitative study of the spit erosion was conducted, using old and recent aerial photographs. Because Si letz Spit has been repeatedly photographed since 1939, 35 years of coverage was available. Study of the aerial photographs revealed cycles of erosion and reformation of the dunes. Periodically, sections of the dunes were eroded. Like the episodes of erosion in 1972-73, this erosion did not extend along the entire 120
28 December 1972 19 January 1973 .-n, •. .. Fi gure 2. Erosion and destruction of the house under construction on lot 226 of Siletz Spit. 121
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Volume 38, No. I January 1976 STATE
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State of Oregon Department of Geolo
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The search for uranium was carried
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Although difficulties have been exp
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Table 1. Oil and gas drilling in Or
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GEOTHERMAL ACTIVITY IN 1975 Donald
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Richard Couch of Oregon State Unive
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Abandonment cementing operations at
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Table 5. Federal geothermal lease s
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21. Ferruginous bauxite and high-al
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8. Geology of Greenhorn District, S
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Volume 38, No.2 Februory 1976 STATE
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Figure 1. View of Mount Hood from s
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Recent Observations on Mount Baker
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A log of all anomalies has been mai
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Figure 6. Breakup of ice within cra
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Figure 8. Photo of East Breach area
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OUR CHANGING RESOURCE CLIMATE Ralph
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FEDERAL MINERALS POLICY OUTLINED BY
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The Ore Bin Published Monthly By ST
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Our research to determine heat flow
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ash-flow tuff. Regional heat flow i
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OPEN FI LE REPORTS ISSUED Oregon De
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AGE OF HOWARD 2 MONTHS, ME 10 The t
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STE ENS MOUN TA I N Volume 38, No.4
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the mountain into three distinct to
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Figure 5. Pike Creek Formation at t
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Figure 7. View east up Little Blitz
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Volume 38, No.5 May 1976 STATE OF O
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Figure 1. Massive rack failure near
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Douglas County. In the 1950's over
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Figure 8 . Damage to the picnic gro
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waves occurred at night during the
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Page 104 and 105: Beaulieu, J.D., and Hughes, P.W., 1
Page 106: Kleppe told the audience that Inter
Page 112 and 113: State of Oregon Department of Geolo
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Page 140: Acknow ledgements This work is a re
Page 143: Components of a 1975 Chevrolet Capr
Page 146: PITTSBURG BLUFF FOSSILS DESCRIBED "
Page 151: State of Oregon Department of Geolo
Page 155 and 156: Figure 4. View of both houses of Fi
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Page 159 and 160: Figure 8. Irregular shorel ine of b
Page 161 and 162: 29 October 1973 10 June 1975 Figure
Page 164 and 165: In 1875 the width of the spit, C, w
Page 169: Volume 38, No.9 September 1976 STAT
Page 172: (often minute) to medium vessels, t
Page 181 and 182: (above) in its increased dorso-vent
Page 183: MINERAL SYMPOSIUM ANNOUNCED The Pac
Page 186: KEEP IN TOUCH! Of course you notify
Page 191: State of Oregon Department of Geolo
Page 197 and 198: " " " EASY GIVING" " " ORE BIN READ
Page 199: TREASURES FROM OLD ORE BINS 25¢ pe
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450 ___ -+---+-________ --+ _____ 4
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BLM ISSUES OIL AND GAS LEASES IN WE
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The Ore Bin Published Monthly By ST
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that some flows, such as the Roza B
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w I I I I 30 60 N . - .t. ..! + S N
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VOLlfIE 38, I'I:J, 12 DeCEMBER 1976
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Ancient terraces: Ancient elevated
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00 00 A u o EJ EXPLANATION Beach sa
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DESCHUTES COUNTY BULLETIN PUBLISHED
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The Ore Bin - Oregon Department of Geology and Mineral Industries

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