Rock Glaciers and Related Landforms in the Sierra
Nevada; Distribution and Climatic Relationships
Connie Millar & Bob Westfall
USFS Sierra Nevada Research Ctr
Albany & Lee Vining, CA
Natural History of Sierran Rock Glaciers
When is Talus Not Just Rock?
A Glacier is a Long-Lasting River of Ice
• Snow transforms to granular ice
• Under pressure ice deforms plastically
• Glacier as a whole flows
• Glacial ice erodes, quarries, & pushes
shattered rocks to front & sides
Kuna Glacier
Dana Glacier
A Group of Frozen-Ground Landforms:
Rock-Ice Features (RIFs)
•
Long-lived glacial & periglacial landforms
•
Comprise either glacial ice overlain by shattered rock,
or a mix of rock & ice
Lake Cyn rock glaciers
Excelsior Rock Glacier
•
Common in arid mountains
where rock debris is abundant
We mapped 421 RIF landforms in
the eastern Sierra Nevada, and
grouped them into five classes:
- Cirque Rock Glaciers
- Valley-Wall Rock Glaciers
- Boulder Streams
- Solifluction Fields
- Patterned Ground
Millar & Westfall, Quat Int, 2008
A Quick Tour…
1. CIRQUE ROCK GLACIERS (RGC)
Mean Elev: 3324m
Shape: 40% L
20%W
40% E
Mean size: 20 ha
Mt Abbott
Mt
Slope Aspects
Karst (sinkhole) ponds
reveal embedded ice
S Fk Pass, S Palisades
Mt Dade
Doug Clark
2. Valley Wall Rock Glaciers (RGV)
Francis Cr Cyn
Mean Elev: 3243m
Shape: 12% L
61% W
27% E
Mean size: 3 ha
E Fk Rock Creek
Slope Aspect
3. Boulder Streams (BSC)
Mean Elev: 3317m
Shape: 39% L
Slope Aspect
7% W
54% E
Mean size: 5 ha
Helen Lk
Kuna Crest
4. Mass Wasting; Solifluction RIFs
Mean Elev: 3509m
Shape: 0% L
0% W
91% E
Mean size: 15 ha
Mts Dana & Gibbs
Slope Aspect
5. Patterned Ground RIFs
Nets & Stripes
Toquima Range, NV
Mean Elev: 3273m
Shape: 33% L
20% W
47% E
Mean size: 1.1 ha
Sorted Circles
Silver Pine Lk, Mt Dunderberg
Slope Aspect
Relict (LIA/Pleistocene) RIFs are also common;
Warren Crest
These appear to lack
persistent ice
25% of mapped features
Dana Cliffs
RIF Climate Modeling:
1. Imported RIF locations into GIS
2. Intersected with 30 arcsec 1970-2000 PRISM data (Daly et al. 1994)
3. Downscaled to RIF locations using regression approach (Hamman & Wang 2005)
Canonical Plot for the First Two
Vectors from Discriminant Analysis
6 RIF Classes and 10 PRISM Climate
Variables
Letters indicate mean of the
distribution for each class
Classes:
A = Scree Boulder Streams
B = Flowing Boulder Streams
C = Solifluction Fields
D = Cirque Rock Glaciers
E = Valley Rock Glaciers
F = Patterned Ground
Comparisons of Pleistocene (P)
vs Holocene (H) Temperatures
Eleven Watersheds with Paired Pleistocene and Holocene RIFs (N = 53)
Two Approaches:
- Elevation Difference x Std Lapse Rate (-6.5C/km)
- Direct PRISM Estimates by Elevation
Pleistocene – Dana Cliffs
Holocene – Kuna Crest
GLACIERS IN A WARMING WORLD
Ice glaciers worldwide have been melting during the past 120 years
Decreases in Area
Dana Glacier, >65%,
Russell 1883
2008
Basagic 2008
Decreases in Mass
S Fk Glacier, WA;
-25%
Fountain 2004
Rock glaciers & RIFs, however, resist melting
and lag in response to warming…
Rock debris insulates
embedded ice against
solar radiation
Pleistocene Rock Glaciers Overrode Tioga Moraines
Lag in Ablation during Warming Climates
Lee Vining Cyn
RG
ine
Tioga lateral mora
RG
RIFs are sources of persistent water
Streams run through the dry season
* Embedded ice is source of water
* Rock mantle reduces evaporation
* Unique air circulation supercools rock matrix
Kuna Lk, Kuna Crest
We install data-loggers in
outlet streams & under
adjacent rocks (air)
RIF outlet streams freeze but don’t dry
iButton Records
Outlet streams freeze
°C
Snow covers
Snow melts
RIF streams & springs were still running
as of late Sept 2007 (extreme dry year)
Dana Fk, Tuolumne
BSC
Whereas many nonRIF streams & springs
dried up
Water chemistry of RIF outlet streams
differs from other Sierran waters
Dave Clow (USGS)
Rock glaciers discharge water different
than ice glaciers
Warren Fork
Water seeps rather than rushes downcanyon & persists through autumn,
even in dry years
Lundy Cyn
RIF canyons often lack central, incised
streams typical of ice-glacial canyons
Pleistocene RGC, Mt Dunderberg
Pleistocene RGC, Gibbs Cyn
Parker Cyn
Lee Vining Cyn
RIFs provide unique wetland alpine habitats
…increasingly rare & important as climates warm
Parker RGC; Pleistocene relict
Gibbs BSC; Holocene active
RIF Wetland Areas (means)
Age
Class
n
-----------Pleistocene
----RGC
-12
Modern
RGC
RGV
BSC
11
8
9
RG
Wetland
Area (ha) Area (ha)
---------------100
252
Dunderberg Pleistocene RGC,
below RG snout
10
2
16
20
5
10
Wetland on
Dunderberg RGC
Plant Species Diversity
RIF Wetland Willow & Sedge Communities
Rock glacier wetlands harbor rare species in otherwise
xeric alpine locations; these wetlands will persist under
warming climates and serve as important plant refugia
Plant Species Diversity - Rock Glacier Surfaces
Barney Rock Glacier Study - Duck Pass, Mammoth Crest
patch
We assessed plant species diversity &
cover on all (60) plant patches
Biogeographic Affinities of Plants on BRG Patches
Soil patches on rock glacier surfaces provide cooler than expected habitats; these
extend the range of higher elevation taxa downward. Patches also provide
“rescue” habitat for lower elevation species stressed by warming climates.
1. Higher Elevation Taxa: 14 spp (47%)
E.g., Erigeron pygmaeus, Eriogonum incanum,
Primula suffrutescens
2. Lower Elevation, Cool/Mesic Taxa: 3 spp (10%)
E.g., Cirsium scariosum,
Pellea breweri
3. Cosmopolitan Mountain Taxa : 18 spp (60%)
E.g., Leptodactylon pungens, Ericameria suffruticosa
60 Plant Patches
7.9% of BRG
1.3% Plant Cover
RIFs provide unique animal habitats
1. Beavers
* Beavers are exotic in the Eastern Sierra widely introduced but minimally established;
* Beavers established in canyons where conditions
support dam-building = low volume streams, widely distributed springs;
* Beavers established in RG Cyns; Beavers further enhance water retention.
Dunderberg Pleistocene RGC
Lundy Pleistocene RGC
2. American Pika
Use rock-glacier surfaces abundantly
Abundant around plant patches - Barney RG
Photo: J Bishop
Abundant near RG snouts
Pika appear to benefit from RIF internal coldair-circulation, cool micro-climates,
Photo: J. Page
…and associated
wetland vegetation
Gibbs Cyn
Summary
•
Rock glaciers & related Rock-Ice Features are widely distributed
in high Sierran canyons, especially east of the crest
•
RIFs store and discharge water persistently and lag in
response to warming
Mt Snowden Rock Glacier
• RIFs
distribute water
broadly across the
landscape
Summary, cont’d
RIFs support persistent wetland habitats otherwise rare in
Sierran alpine regions & high plant species diversities
•
Sherwin Crest RGs
•
RIFs provide cold microclimates
and habitat for wide range of
plant species on soil “islands”
• RIFs
support important habitat
for wetland and cool-dependent
animals, including abundant
refugial habitat for pika
Photo: A. Shcherbina
phew