Open-File Report 96-460
“THE GREAT CATARACT” Effects of Late Holocene Debris Flows on Lava Falls Rapid, Grand Canyon National Park, Arizona
Abstract
Introduction
Purpose and Scope
Acknowledgments
Characteristics of Debris Flows in Grand Canyon
Debris Flows and the Colorado River
Methods
The Prospect Valley Drainage Basin
Historical Photographs of Lava Falls Rapid
Mapping and Age Determinations for Debris-Flow Deposits
Pedogenic Calcium Carbonate
3He
Desert Plant Assemblages
Clonal Rings of Creosote Bush
14C
Climatic and Hydrologic Data
Characterization of Debris Flows and Debris Fans
Discharge Estimates and Water Content
Surface Area and Volume
Constrictions
Surficial Geology of The Prospect Debris Fan
General Debris Fan Characteristics
Fan-Forming Debris-Flow Surfaces
tfa
tfb
tfc
Inset Debris-Flow Surfaces
tia
tib
tic
tid
tie
tif
tig
tih
tii
tij
Colluvium and Steep Slopes
tc
Reworked Debris-Flow Deposits
rwr
rwc
rwfd
Historical Change in Lava Falls Rapid
Navigation of Lava Falls Rapid in 1994
The Wide, Stable Rapid(1872-1939)
The Period of Frequent Debris Flows (1929-1966)
Quiescence (1966-1995)
The 1995 Debris Flow
Initiation of Debris Flows in Prospect Canyon
Hydroclimatology
The Firehose Effect
Magnitude and Frequency of Debris Flows
Discharge Estimates
Volumes of Debris Flows
Constrictions of the Colorado River
Frequency of Debris Flows
Reworking of Debris Fans by the Colorado River
Discussion and Conclusions
References Cited
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