GRAND CANYON HOL

GRAND CANYON HOL

GEOMORPHOLOGY SYM

GEOMORPHOLOGY SYM

February 8 February 8

-10, 20

10, 20

CONCLUDING OBSERV

CONCLUDING OBSERV

By

Dr. Alan Howard Dr. Alan Howard

Dr. Gordon Grant Dr. Gordon Grant

Dr. Michael Blum Dr. Michael Blum

Mr. Fred Mr. Fred Nials
GRAND CANYO

GRAND CANYO

GEOMORPHOLOG

GEOMORPHOLOG

KEY ISSUES KEY ISSUES

• Long

-Term Evolution: Geomorph

Term Evolution: Geomorph

• Post

-Dam Channel Bed Changes Dam Channel Bed Changes 

• Holocene Landscape Evolution: Holocene Landscape Evolution: T

 T

• Erosion of the Holocene Record: 

Erosion of the Holocene Record: 
LONG-TERM LANDSCAPE EV

TERM LANDSCAPE EV

THE GEOMORPHIC CON

THE GEOMORPHIC CON

• Long-term (10 term (105-106 years) incisional incisional tren

tren

flight of Pleistocene terraces flight of Pleistocene terraces

• Well-defined variations in valley morpho

defined variations in valley morpho

corresponding preservation of depositio

corresponding preservation of depositio

the downstream direction correlate with the downstream direction correlate with 

structure structure

• Long profile details are controlled by ba

Long profile details are controlled by ba

debris-flow inputs and their reworking b

flow inputs and their reworking b

stream 

• Clear contrasts in fluvial processes and 

Clear contrasts in fluvial processes and 

the glacial and interglacial river the glacial and interglacial river

WHAT DO WE KNOW? WHAT DO WE KNOW?
LONG-TERM LANDSCAPE EV

TERM LANDSCAPE EV

THE GEOMORPHIC CON

THE GEOMORPHIC CON

• A better understanding of the initial con

A better understanding of the initial con

the Holocene, and the archaeological re

the Holocene, and the archaeological re

did the river reach its present level? did the river reach its present level? 

• Has it flowed at a lower level? Has it flowed at a lower level?

• Is this its lowest elevation or depth o

Is this its lowest elevation or depth o

WHAT DO WE REALLY NEED T

WHAT DO WE REALLY NEED T
POST-DAM CHANGES IN C

DAM CHANGES IN C

MORPHOLOGY AND PRO

MORPHOLOGY AND PRO

• Solid understanding of sedime Solid understanding of sediment routing 

nt routing 

especially the coupling between tributary 

especially the coupling between tributary 

main stem main stem

• Solid understanding of the major changes 

Solid understanding of the major changes 

supply due to dam construction, especial

supply due to dam construction, especial

sediment sediment

• Reasonable understanding of relations be

Reasonable understanding of relations be

deposition along the channel margin and 

deposition along the channel margin and 

we know how to build a beach we know how to build a beach

WHAT DO WE KNOW? WHAT DO WE KNOW?
POST-DAM CHANGES IN C

DAM CHANGES IN C

MORPHOLOGY AND PRO

MORPHOLOGY AND PRO

• Deposition and erosion of fine vs. coarse 

Deposition and erosion of fine vs. coarse 

different trajectory different trajectory

• The dam The dam-proximal reach has degraded sig

proximal reach has degraded si

• Farther downstream, there has been no n

Farther downstream, there has been no n

even slight even slight aggradation aggradation, of the channel be

, of the channel be

• The channel bed has, however, been tran

The channel bed has, however, been tran

mixed gravel mixed gravel-sand system to a highly enh

sand system to a highly enh

channel channel

WHAT WE KNOW WHAT WE KNOW - CONT.
POST-DAM CHANGES IN C

DAM CHANGES IN C

MORPHOLOGY AND PRO

MORPHOLOGY AND PRO

WHAT DO WE REALLY NEED TO 

WHAT DO WE REALLY NEED T

• How do we disentangle the effects of the 

How do we disentangle the effects of the 

inherited trajectory of channel change d

inherited trajectory of channel change d

changing climate? changing climate? 

• This may be a fundamentally This may be a fundamentally unresol

unresol

we should try. we should try.

• We need to know more about the natura

We need to know more about the natura

climate and fluvial processes. climate and fluvial processes.

• How do we preserve a beach? What seq

How do we preserve a beach? What seq

what level of sediment supply are neede

what level of sediment supply are neede
HOLOCENE LANDSCAPE EV

HOLOCENE LANDSCAPE EV

THE TERRACES THE TERRACES

WHY IS THIS IMPORTANT? WHY IS THIS IMPORTANT?

• Holocene terraces correspond to the tim

Holocene terraces correspond to the tim

human occupation, and represent the re

human occupation, and represent the re

cultural resources and dateable material cultural resources and dateable materia

• Holocene terraces record human Holocene terraces record human

-landsc

landsc

interactions, and the nature of the enviro

interactions, and the nature of the enviro

particular points in time particular points in time

• The Colorado River integrates surface p

The Colorado River integrates surface p

large area of the American large area of the American West. Holoce

West. Holoce

the best record of fluvial activity, and ch

the best record of fluvial activity, and ch

activity through time in response to clim

activity through time in response to clim

other factors other factors
HOLOCENE LANDSCAPE EV

HOLOCENE LANDSCAPE EV

THE TERRACES THE TERRACES

WHAT DO WE KNOW? WHAT DO WE KNOW?

• Reasonably agreed Reasonably agreed

-upon sequence of de

upon sequence of de

• Deposits are well Deposits are well

-mapped (lines on the m

mapped (lines on the m

good) in many areas, including the cultu

good) in many areas, including the cultu

areas

• Deposits consist of Deposits consist of overbank overbank fluvial, fluvial, col

col

facies of varying proportions of varying proportions

• At any one reach where mapping has be

At any one reach where mapping has be

deposits are reasonably well deposits are reasonably well

-dated
• How deposits precisely correlate from rea

How deposits precisely correlate from rea

between Grand Canyon and other areas between Grand Canyon and other areas

• Genetic origins of these landforms and de

Genetic origins of these landforms and de

• Depositional environments and relativ

Depositional environments and relativ

fluvial, fluvial, eolian, and colluvial colluvial inputs

• Splitting vs. lumping of units....which 

Splitting vs. lumping of units....which 

• Origin and position of basal Origin and position of basal erosional erosional 

implications for river incision history implications for river incision history

• Role of “extreme” vs. “normal” floods Role of “extreme” vs. “normal” floods 

• How much of the record is missing How much of the record is missing - parti

parti

to middle Holocene? What are the implic

to middle Holocene? What are the implic

geological and archaeological interpretat

geological and archaeological interpretat

• How is the terrace record coupled to exte

How is the terrace record coupled to exte

WHAT WE ARE LESS CERTAIN A

WHAT WE ARE LESS CERTAIN A

HOLOCENE LANDSCAPE EV

HOLOCENE LANDSCAPE EV

THE TERRACES THE TERRACES
EROSION OF THE HOLOCENE 

EROSION OF THE HOLOCENE 

THE GULLIES THE GULLIES

WHY IS THIS IMPORTANT? WHY IS THIS IMPORTANT?

• Thought to be the primary short Thought to be the primary short

-term m

term m

loss of cultural resources loss of cultural resources

• Has been proposed to be, at least partia

Has been proposed to be, at least partia

operations of Glen Canyon Dam operations of Glen Canyon Dam 
EROSION OF THE HOLOCENE 

EROSION OF THE HOLOCENE 

THE GULLIES THE GULLIES

• Fluvial landscapes are in a constant state 

Fluvial landscapes are in a constant state 

for any given flood stage, there are locat

for any given flood stage, there are locat

deposition, and subsequent modification deposition, and subsequent modification 

• Gully erosion happens, and the only r

Gully erosion happens, and the only 

front-burner here is the proposal that 

here is the proposal that 

erosion is due to dam presence and/o

erosion is due to dam presence and/o

and the associated mandate to prese

and the associated mandate to prese

resources resources

• Gullies always grow in the Gullies always grow in the headward headward 

tend to be initiated at some break in s

tend to be initiated at some break in s

• Reasonable evidence exists that accelera

Reasonable evidence exists that accelera

corresponds to the post corresponds to the post

-dam period dam period

WHAT DO WE KNOW? WHAT DO WE KNOW?
• The post The post-dam period corresponds to one 

dam period corresponds to one 

periods in the historical record periods in the historical record

• We see no clear evidence that gullies are 

We see no clear evidence that gullies are 

related processes related processes

• Flood sediments can fill gully mouths, an

Flood sediments can fill gully mouths, an

years to exert short years to exert short-term influences on th

term influences on th

of gully networks (to the first of gully networks (to the first nickpoint nickpoint?)

• We see no clear evidence that deposition 

We see no clear evidence that deposition 

sediments in gully mouths will heal exist

sediments in gully mouths will heal exist

permanently stem gully erosion, or have 

permanently stem gully erosion, or have 

the long the long-term evolution of gully systems term evolution of gully systems

• The supply of sand for The supply of sand for eolian transport, a

transport, a

healing of gullies, has decreased due to d

healing of gullies, has decreased due to 

WHAT DO WE KNOW WHAT DO WE KNOW - CONT.

EROSION OF THE HOLOCENE 

EROSION OF THE HOLOCENE 

THE GULLIES THE GULLIES
• Exact links between gully erosion and “ba

Exact links between gully erosion and “ba

well understood well understood

• If gullies are graded to the low flow ch

If gullies are graded to the low flow ch

level has been raised due to dam pres

level has been raised due to dam pres

• If gullies are graded to sand bars, then 

If gullies are graded to sand bars, the

base level has been lowered due to da

base level has been lowered due to da

• How does something called base leve

How does something called base leve

to gullies on the upper terraces? to gullies on the upper terraces?

• What are the precise controls on gully ini

What are the precise controls on gully ini

propagation vs. gully healing (senescenc

propagation vs. gully healing (senescenc

• What are the longer What are the longer-term effects of gully m

term effects of gully 

especially the “unintended consequences

especially the “unintended consequences

WHAT WE ARE LESS CERTAIN A

WHAT WE ARE LESS CERTAIN A

EROSION OF THE HOLOCENE 

EROSION OF THE HOLOCENE 

THE GULLIES THE GULLIES
WHERE TO FROM H

WHERE TO FROM H

• Develop a true, fully integrated interdiscip

Develop a true, fully integrated interdiscip

perspective and methodological approach 

perspective and methodological approac

Canyon archaeological and human ecolog

Canyon archaeological and human ecolo

• Given the dynamic nature of the landscap

Given the dynamic nature of the landscap

budgets, all archaeological resources sho

budgets, all archaeological resources sho

considered of equal significance and valu

considered of equal significance and valu

• Develop a rational strategy to maximize re

Develop a rational strategy to maximize re

investment by driving archaeological and 

investment by driving archaeological and 

ecological research with fundamental que

ecological research with fundamental que

• Comprehensive evaluation of sites rel

Comprehensive evaluation of sites re

geomorphic setting and geomorphic setting and paleolandsca

paleolandsca

• Clear understanding of the archaeolog

Clear understanding of the archaeolog

of “at risk” and non at of “at risk” and non at

-risk sites, and w

risk sites, and 

can be answered from each can be answered from each
WHERE TO FROM H

WHERE TO FROM H

• At the gully scale gully scale, build on past and curre

, build on past and curre

develop fully predictive physical models o

develop fully predictive physical models 

potential and site vulnerability potential and site vulnerability

• At the landscape scale landscape scale, undertake a new g

, undertake a new 

detailed and integrated studies that focus 

detailed and integrated studies that focus 

of the archaeological record and Holocen

of the archaeological record and Holocen

evolution: evolution:

• Process Process

-based studies of Holocene fr

based studies of Holocene fr

fully understand origin and genetic sig

fully understand origin and genetic si

stem landforms and deposits stem landforms and deposits 

• Geochronology needs to be more fully 

Geochronology needs to be more fully 

through creative and extensive use of 

through creative and extensive use of 

as 14C, OSL, and C, OSL, and cosmogenic cosmogenic nuclides nuclides

• How do recordsof recordsof landscape evolutio

landscape evolutio

regional vs. global climate and climate 

regional vs. global climate and climate