Transcript Open Basin Lakes

Open Basin Lakes:
Surface Water Inventories and
Sources of Water
Open vs. Closed
Basins
Lakes that were once hydrologically
open (basins with outlets) allow:
• Confident recognition of where
water ponded
• Measurement of the minimum
volume of water required (to
activate an outlet valley)
Open
Basin
In basins without clearly incised
outlets, we cannot be sure that water
ponded.
Closed
Basin
Open Basin Locations
Parameters
Measured
All lakes:
• Connections to other lakes
(lake chains)
• Elevation
• Area, volume, perimeter
• Morphological characteristics
(resurfacing? sedimentary
deposits? )
Where possible:
• Watershed Area
Lake Size
Eridania Basin
Ma’adim Vallis
(to Gusev Crater)
Irwin et al., 2002 (Science)
V=213000 km3, WA=2080000 km2, V/Aw=102 m
Lake Volume / Watershed Area
Volume/Watershed Area =
a measure of the water
that was delivered to the
lake per unit area of the
watershed
If groundwater is
negligible, this is the
integrated precipitation
amount over time (in
excess of evaporation /
infiltration) necessary to
flood the basin.
Eridania
in meters
Lake Volume / Watershed Area
Cassini
Cassini Crater
V=30000 km3
WA=155000 km2
V/Aw=200 m
in meters
Lake Volume / Watershed Area
Antoniadi
Antoniadi Crater
V=31000 km3
WA=555000 km2
V/Aw=56 m
in meters
Lake Volume / Watershed Area
88.25E, 3.25S
V=400 km3
WA=17000 km2
V/Aw=23 m
128.75E, 8.3S
V=1700 km3
WA=61000 km2
V/Aw=28 m
Many basins that remained closed have V/Aw ~20-30 m.
Lake Volume / Watershed Area
Given that closed basins had
V/Aw ~20-30 m, open basins
with high V/Aw either had to
have:
1.
Especially high local
‘excess’ precipitation
(*unlikely*),
OR
2.
A regional (non-local!)
groundwater contribution
to flooding the basin.
in meters
Lake Volume / Watershed Area
Symbol size proportional to V/Aw
Anomalies in V/Aw are:
i) larger lakes than is typical
ii) generally at low elevations
iii) most are concentrated in “greater Arabia” (70%)
Modeled Evaporation Rate (10-4 m/yr): a
proxy for where groundwater reaches surface
Andrews-Hanna et al., 2008
•
Broad regional
agreement between
where models expect
groundwater to outcrop
and where we observe
it.
•
Some differences (e.g.,
for largest lakes):
Cassini & Eridania
clearly resolved as net
positive groundwater
flux.
Antoniadi+Tikhonravov,
not resolved in regional
models, but seen in
higher res. models
Andrews-Hanna et al., 2008
Water Source
•
Lake/Watershed
properties & modeling
suggest an important role
for groundwater input to
some lakes
•
Lakes that are not
anomalies in V/Aw have
volume proportional to
watershed area:
consistent with local
precipitation + local
precipitation-recharged
groundwater as water
sources.
Resurfacing
of large
lake floors
Hesperia
Planum
MOLA Roughness
The rule, not
the exception.
>50% of
catalogued
lakes mapped
have textures &
morphological
indicators of
post-lacustrine
resurfacing.
MOLA Roughness data
Kreslavsky and Head, 2000
Goldspiel and Squyres (1991) recognized that
“in many instances, the sedimentation basin floors
appear to be covered by volcanic extrusions...postdat[ing] the period of fluvial activity.”
Resurfacing
of large
lake floors
The rule, not
the exception.
“Other features to note...[are] the signs of volcanic
extrusions on the crater floor.”
>50% of
catalogued
lakes mapped
have textures &
morphological
indicators of
post-lacustrine
resurfacing.