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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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