Figure 1. Topography of Ma'adim Vallis, showing the Ma'adim basin rim crosscut at (c) and at the valley head (a), dissected basin floor (b), Gusev crater (d), its exit breach (e), and undissected lowlands (f). Figure is MOLA topography with 100-m interval, cylindrical projection.1
Our research concerns the potential for past lakes in the Martian highlands and to quantify their characteristics. The presence of standing bodies of water on the Martian surface would tell us a great deal about the past climate. Lakes, more so than river channels, requires a warmer climate with either a ground water or precipitation recharge system, and they may represents formerly habitable sites.
The best means for identifying paleolakes are through deltas and continuous terraces at a constant elevation around a basin1, or breached basins2 that have either a contributing valley, and outlet, or both, but no incision of the lower-lying basin floor. Shore landforms, as exhibited by terrestrial lakes, are typically small and fine-grained potentially preventing their observation and preservation on Mars, particularly as the available topographic data have coarse resolution. Understanding the range and configuration of the paleolake features at the imaging resolution level is one of our objectives.
Ma'adim Vallis, shown in Figure 1, was carved by the overflowing a paleolake up to ~1.1 million km2 in size, located in the Eridania basin south of the valley's source spillways2. This discovery demonstrates that large areas of the highlands were formerly flooded with water. The spillway, which represents the channel's elevation when it overflowed, provides the most compelling evidence that a former lake existed. Moreover, the Eridania basin's interior contains six highly degraded impact craters2 that have bowl-shaped rather than flat floors indicating that sediment accumulated mainly along their margins1,2 in standing bodies of water. It is hard to reconcile a large, long-lived lake at this high elevation without some means of recharging highland aquifers. The topography suggests that precipitation was the ultimate water source1 for the lake, and catastrophic flooding of this lake was the primary eroding agent of the large Ma'adim Vallis valley1,2.
For more information about the role of these crater paleolakes and relationship between paleolakes and valley networks see Late Stage Fluvial Processes.
1. Irwin et al. (2002), A Large Paleolake Basin at the Head of Ma'adim Vallis, Mars.
2. Irwin et al. (2004), Geomorphology of Ma'adim Vallis, Mars, and associated paleolake basins.
3. Irwin et al. (2005), An intense terminal epoch of widespread fluvial activity on early Mars: 2. Increased runoff and paleolake development.
Dr. Maxwell's Homepage
Dr. Irwin's Homepage
Back to List of Mars research