Overspilling small craters on a dry Mars: Insights from breach erosion modeling
Introduction
Surface liquid water on Mars requires conditions very different from the present day; either temperatures >273 K resulting from different climate conditions, or transport of water out of the subsurface for example by groundwater outflows (Rodriguez et al., 2015). If the water source is known, morphological features (e.g. fluvial channels, lake deposits) can be used to understand either the evolution of the Martian climate and atmosphere, or the evolution of the hydrosphere. Wet events on Mars since the Valley Network forming period (<3.2-3.9 Ga) (Hartmann, 2005) are recorded by the formation of features such as alluvial fans (Kite et al., 2019; Hauber et al., 2013), and small exit breach craters or “pollywogs” (Wilson et al., 2016). These features indicate a trend from an earlier, wetter climate with intense fluvial erosion (Matsubara et al., 2013), to arid conditions punctuated by occasional surface liquid water (Kite et al., 2019). Pollywogs have outlet valleys extending from well-preserved crater rims, but no inlet valleys (Wilson et al., 2016) e.g. Fig. 1a. The outlet valleys formed by overspill of water from within the crater. Fresh pollywog rims indicate that pollywog outlet incision post-dates the intense Late Noachian and Early Hesperian fluvial activity (Wilson et al., 2016). Pollywog formation requires a water source that left crater rims intact, but was intense enough to supply m3 of water under dry climate conditions. Two possible sources of this water are groundwater (e.g. from a pressurized aquifer at depth), and precipitation and/or melting (Fig. 2). If erosion during a single pollywog overspill event can be constrained, then the observed erosion from pollywog overspill events is an important constraint on the number, duration, and intensity of mid-latitude surface liquid water events on Mars since the Late Noachian/Early Hesperian (3.9-3.2 Ga) (Hartmann, 2005).
Low-latitude alluvial fans require multiple episodes of wetting (Hauber et al., 2013; Kite et al., 2019). Groundwater modeling has shown that outflow channel formation may be more consistent with multiple, smaller-magnitude groundwater discharge events than a single flood (Andrews-Hanna and Phillips, 2007). However, other features are consistent with a single wet event, for example impact-driven melting and precipitation in Mojave and Hale craters (Goddard et al., 2014). Do pollywogs belong to the first group of features (Gale, alluvial fans) that record signatures of global climate conditions during the Hesperian? Or do they result from localized groundwater or impact-induced conditions?
Global climate and local conditions are plausible explanations for pollywogs. Accumulating sufficient surface liquid water to overspill a pollywog through precipitation and snowmelt is challenging in a climate that is consistent with low erosion rates (Golombek et al., 2006) and valley distributions and morphologies consistent with reduced precipitation rates relative to the Noachian (>3.6-3.7 Ga) (Harrison and Grimm, 2005). Models of Martian climate under different orbital conditions can produce ice accumulation in midlatitudes (Mischna et al., 2013), and some melting (Kite et al., 2013). This makes ice-filled craters with melt ponds on their surfaces a plausible watersource for pollywog outlet valley erosion (e.g. Fig. 2). Orbital changes provide a potential mechanism for pacing surface liquid water activity (Jakosky et al., 1995). Large impacts (Steakley et al., 2019; Turbet et al., 2020) may also be able to induce short-lived climates enabling surface liquid water. Groundwater discharge from pressurized aquifers is an alternative mechanism for supplying liquid water to the surface during the Hesperian (Andrews-Hanna and Phillips, 2007; Rodriguez et al., 2015), e.g. in Xanthe Terra (Coleman, 2005), and some large (D>30 km) crater lake breach valleys (Warner et al., 2010).
The expected valley floor erosion from a single pollywog overspill event compared with observed erosion depths is an important constraint on Mars' climate and hydrology since the Late Noachian/Early Hesperian (Fig. 1a) because it can be used to infer the properties of the pollywog-overspilling water source. In this paper, we determine whether pollywog exit breach valleys are consistent with a single overspill event, or if their formation requires multiple overspill events. We use a new fixed channel width 0-D model (Section 2.1) and pollywog measurements from HiRISE Digital Elevation Models (DEMs) (Section 3.1) to predict the erosion that can occur in a single crater overspill event. The model is ground-truthed using terrestrial dam breach flood data (Section 3.2). We compare model predictions and observed breaches (Section 4), and consider the climate and hydrological conditions under which all studied pollywogs could be consistent with a single overspill event (Section 5).
Section snippets
Methods
In Section 2.1 we describe our new model for breach erosion. In Section 3.1 we describe our pollywog measurements, their implications, and how they are used in the breach erosion model. In Section 3.2 we test the model against terrestrial exit breach erosion events.
Results
We apply our model to Mars pollywogs (Section 3.1) and terrestrial breach erosion events compiled from the literature (Section 3.2).
Runaway erosion: predicted but not observed
Runaway erosion is observed for many terrestrial moraine/landslide dam breaching events (i.e. erosion to the base of the dam), whether the dam is a landslide deposit, terminal moraine, or crater rim. Runaway erosion is not observed for any pollywog valleys. Pollywog exit breaches do not erode deeply relative to crater floor depth (Fig. 1). By contrast, megaflood-formed valleys in Xanthe Terra erode hundreds of meters of crust (Coleman, 2005), representing 80 to 100% of the available relief
Are all pollywogs consistent with a single overspill event?
The transition between breaches consistent with a single overspill event and breaches that require multiple breaching events or continuous supply of water (termed “multiple event” breaches) depends on how fast the lake can drain relative to the size of the lake. This can be quantified using the ratio of an outlet valley, and of the pollywog crater and outlet valley. The power of 7/6 is inherited from Eqs. (6) & (8). We define the transition as the value of that allows for
Conclusions
Pollywogs are relatively young Martian craters with outlet valleys puncturing fresh crater rims, but no visible inlet valleys. Our new fixed channel width, 0-D model of breach erosion predicts runaway erosion for 2 of 21 measured pollywog crater exit breaches, but evidence for runaway erosion (defined here as erosion through the entire crater rim thickness) is not observed for any pollywogs. The mismatch between our model predictions and the measured pollywog valleys cannot be explained by
CRediT authorship contribution statement
A.O. Warren: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Visualization, Writing – original draft. S. Holo: Methodology, Resources, Software, Writing – review & editing. E.S. Kite: Conceptualization, Funding acquisition, Supervision, Writing – review & editing. S.A. Wilson: Resources, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We thank Caleb Fassett for pointing out low latitude pollywogs, and the HiWish program for targetting requested pollywogs. We would also like to thank Tim Goudge and an anonymous reviewer for their insightful comments and suggestions which helped clarify the manuscript. We thank Shavonne Morin at the University of Arizona for producing the DEM in Fig. 1. All stereopairs are publicly available on the HiRISE website. Our DEMs are publicly available at https://uchicago.box.com/v/pollywog-DEMs2020.
References (51)
- et al.
A review of catastrophic drainage of moraine-dammed lakes in British Columbia
Quat. Sci. Rev.
(2000) - et al.
Supraglacial and proglacial valleys on Amazonian Mars
Icarus
(2010) - et al.
Valley network-fed, open-basin lakes on Mars: distribution and implications for Noachian surface and subsurface hydrology
Icarus
(2008) Martian cratering 8: isochron refinement and the chronology of Mars
Icarus
(2005)- et al.
Seasonal melting and the formation of sedimentary rocks on Mars, with predictions for the Gale Crater mound
Icarus
(2013) - et al.
New insights into the mechanics of fluvial bedrock erosion through flume experiments and theory
Geomorphology
(2015) - et al.
Valley formation by groundwater seepage, pressurized groundwater outbursts and crater-lake overflow in flume experiments with implications for Mars
Icarus
(April 2014) - et al.
Testing the impact heating hypothesis for early Mars with a 3-D global climate model
Icarus
(2019) - et al.
The environmental effects of very large bolide impacts on early Mars explored with a hierarchy of numerical models
Icarus
(2020) - et al.
Bedrock rivers
Applicability of sediment transport capacity formulas to dam-break flows over movable beds
J. Hydraul. Eng.
Hydrological modeling of outflow channels and chaos regions on Mars
J. Geophys. Res., Planets
Flow depth in sand-bed channels
J. Hydraul. Eng.
Slope correction for calculation of bedload sediment transport rates in steep channels
J. Hydraul. Eng.
On the extreme rainfall of Typhoon Morakot (2009)
J. Geophys. Res., Atmos.
Martian megaflood-triggered chaos formation, revealing groundwater depth, cryosphere thickness, and crustal heat flux
J. Geophys. Res., Planets
Bed-load sediment transport on steep longitudinal slopes
J. Hydraul. Eng.
Open-Channel Hydraulics
Mechanisms and timescales of fluvial activity at Mojave and other young martian craters
J. Geophys. Res., Planets
Erosion rates at the Mars exploration rover landing sites and long-term climate change on Mars
J. Geophys. Res., Planets
Incision of paleolake outlet canyons on Mars from overflow flooding
Geology
Hydrological modeling of the Martian crust with application to the pressurization of aquifers
J. Geophys. Res., Planets
Groundwater-controlled valley networks and the decline of surface runoff on early Mars
J. Geophys. Res., Planets
Asynchronous formation of hesperian and Amazonian-aged deltas on Mars and implications for climate
J. Geophys. Res., Planets
Dynamics of Mars lake-overflow valley incision
Cited by (11)
Geomorphic response of outburst floods: Insight from numerical simulations and observations––The 2018 Baige outburst flood in the upper Yangtze River
2022, Science of the Total EnvironmentCitation Excerpt :However, quantifying the geomorphological responses of canyon landforms to outburst flood events is key to understanding not only historical records and risk evaluation (Tweed and Russell, 1999) but also the full time spectrum of landscape evolution, linking the short-term extreme event scale to the long-term geological timescale (Garcia-Castellanos and O'Connor, 2018). In recent years, as a growing amount of geological evidence related to megafloods has been discovered on Earth and Mars (Baker, 2002; Carling, 2013; Carling et al., 2009; Goudge et al., 2021; Lapotre et al., 2016; Liu et al., 2020; Warren et al., 2021), studies of the relationships between outburst floods and fluvial morphodynamics in mountainous canyon areas have attracted increasing interest. In turn, multiple erosion and sedimentation models have been proposed to explain the effects of outburst floods on canyon topography (David et al., 2022; Larsen and Lamb, 2016; Miyamoto et al., 2007).
Seepage-evaporation controlled depletion of initially water-filled reservoirs on Earth and Mars: Analytic versus HYDRUS modeling
2022, IcarusCitation Excerpt :At t = 0, the pond started to empty due to two draining factors: seepage and evaporation. We note that Warren et al. (2021) studied a “reverse” process of extravasation of groundwater through the bottom of a water-filled Martian crater, albeit taking into account dynamics of axisymmetric surface water flow hydraulics downslope crater's rim. We ignore evaporation of liquid pore water into soil-atmosphere vapor, albeit on the time scale of post-extinction dynamics of a subsurface hydrological system, evaporation-sublimation becomes an important component of the Martian hydrological cycle (see, e.g., Baum and Wordsworth, 2020, Fukushi et al., 2019, Grimm et al., 2017, Lark et al., 2020).
3-D geophysical modeling of a buried, simple impact crater: Holleford impact structure, Ontario, Canada
2024, Meteoritics and Planetary ScienceRemote Sensing and Data Analyses on Planetary Topography
2023, Remote SensingAssessing Controls on the Incomplete Draining of Martian Open-Basin Lakes
2023, Journal of Geophysical Research: PlanetsHigh and Dry: Billion-Year Trends in the Aridity of River-Forming Climates on Mars
2022, Geophysical Research Letters