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The Navua Valles are comprised of a system of channels and valleys on the inner Northeastern rim of Hellas Basin, which is a 1500-km-long sloping terrain. Drainage systems and regional geology in this unique setting were not previously mapped in detail. We mapped this region using CTX (6 m/px) as the base map and assessed surface unit ages resulting from our crater counting. We found that the timing of the deposit-forming episodes in this region during the Hesperian and Early to Middle Amazonian largely correlated to active phases of the Hadriacus Mons volcanic center. We found evidence for several episodes of fluvial activity Hesperian to the Amazonian with declining intensity, and transitioning to ice-dominated processes. The channels in the Navua Valles region erode into deposits dating from the Noachian to Early Amazonian, including the Noachian highlands, Noachian to early Amazonian crater ejecta, and likely volcanic plains formed from the Hesperian to the Hesperian–Amazonian transition. Channels directly originating from Hadriacus Mons are younger, while precipitation-fed channels at larger distance from the volcanic center are older, indicating different triggers for fluvial activity. Crater counting results indicate that almost all channel floors were at least partially resurfaced during the Amazonian and that several channel deposits formed during the last 0.5 Gyr. Water pathways likely included surface channels, lakes, and subsurface flow. The Navua Valles channel system is discontinuous, and the number of terminal deposits (sink locations) is almost as high as the number of channel sources, which is unusual for valley networks elsewhere on Mars. Interior channels formed only in the major Navua channels, they are even more fragmented than their parent channels, but occur along their entire length. Channels and valley systems within the Navua Valles are potential targets for in situ astrobiological studies, as they could have provided potential habitats at least periodically, from the Late Hesperian to the Late Amazonian.

Volcanic channels are common features on the terrestrial planets. They have diverse morphologies including sinuous rilles, channelized flows, and potentially collapsed lava tubes. Many of these channels are a part of a typical igneous assemblage of landforms. In addition, some channels have an ambiguous origin, where a volcanic interpretation explains many of the observed features in some settings. This chapter describes volcanically formed sinuous channels, pitted channels, channelized flows, streamlined forms, platy terrain, and discusses a potential volcanic context for outflow channels and some valley networks on Mars.

The Navua Valles are systems of paleodrainages located north of Dao Vallis, which empty into Hellas Planitia, the largest impact basin on Mars. In this study, we mapped and characterized the Navua Valles Region's individual drainage systems, including drainages along the southwestern flank of Hadriacus Mons, and one valley network from the same source as Navua Valles but flowing in the opposite direction. The major drainage systems share morphological characteristics common to both outflow channels and valley networks. The slopes in this region are dissected by two major Navua drainage systems (here Navua A* and B*) and several shorter, sub-parallel valleys formed on the highest gradient (approximately 20 m/km [1.15°]) slopes, at the lowest part of Hellas Basin's rim. The two major drainage systems originate in the highlands, and empty into the basin. Our mapping suggests that water in Navua Valles reached the basin floor in a complicated descent and included several episodes of surface ponding, surface runoff, infiltration, subsurface flow and subsequent outflow. The most prominent channel system, Navua A, forms a repetitive sequence of deep incision into bedrock, followed by a transition into broad channels in erodible materials, and then into unconfined deposits. This successive erosion–transport–deposition sequence continues to repeat along the valley's entire length forming a discontinuous pattern that is consistent with classical fluvial process models. The channels cut into volcanic plains likely emplaced from the formation of Tyrrhenus and Hadriacus Montes. The dendritic source valleys of Navua A originate from the rim of a highland crater while the rest of this subsystem consists of a single, discontinuous channel which is consistent with a single water source zone that likely supplied water for all channels downslope. These drainages may have formed as discontinuous channels, revealing the potential existence of subsurface drainage pathways located within an approximately 1.5 × 10 5 km 2 area. Water transported underground emerged in segments that are either isolated or aligned downslope from each other. We have identified several causes of discontinuities, located the zones of potential ground-water discharge and recharge, and a site of localized precipitation at the headwaters of Navua A.

(1) A network of subsurface wedges that are composed of a mixture of ice and sand or rubble. Ice and sand layers may alternate within a wedge (Berg and Black 1966). They can be distinguished from other composition wedges by the presence of accessory landforms, such as gullies. (2) A frost-fissure polygon net showing evidence of both primary and secondary filling: ▶ sandwedge polygon (Harris et al. 1988 and references therein).

To search for local and global scale geologic associations that may be related to the internal dynamics of Io, we have completed a global catalog of all mountains and volcanic centers. We have identified 115 mountain structures (covering approx. 3% of the surface) and 541 volcanic centers, including paterae (calderas and dark spots) and shield volcanoes. The average length of an Ionian mountain is 157 km, with the longest being 570 km. The mean height of Ionian mountains is 6.3 km, and the highest known mountain is Boosaule Montes (17.5 +/- 3 km). Five basic morphologic types of mountains have been identified; mesa, plateau peak, ridge, and massif. Very few mountains bear any physical similarity. to classic volcanic landforms, but many resemble flatiron mountains on Earth and are interpreted as tilted crustal blocks. This would be consistent with the hypothesis that most mountains are thrust blocks formed as a result of compressive stresses built up in the lower crust due to the global subsidence of volcanic layers as they are buried over time. More than one mechanism may be responsible for all Ionian mountains, however. The proximity of some mountains to paterae may indicate a direct link between some mountains and volcanism, although it is not always clear which came first. In contrast to earlier studies, a pronounced bimodal pattern is observed in the global distribution of both mountains and volcanic centers. The regions of highest areal densities of volcanic centers are near the sub- and anti-Jovian regions, but are offset roughly 90deg in longitude from the two, regions of greatest concentration of mountains. This anticorrelation may indicate the overprinting of a second stress field on the global compressive stresses due to subsidence. The bimodal distribution of volcanic centers and mountains is consistent with models of asthenospheric tidal heating and internal convection developed by Tackley et al.Over regions of mantle upwelling, compressive stresses in the lower crust induced by global subsidence might be reduced, encouraging volcanism and discouraging mountain building. In regions of mantle downwelling, these compressive stresses in the lower crust might be increased, discouraging volcanism and encouraging mountain building. Alternatively, the global pattern may be related to possible (but undocumented) nonsynchronous rotation of lo, which would produce two regions each of compression and extension in the crust. Evidence of layering and of mass wasting, including landslides, block sliding, debris aprons and downslope creep, on Ionian mountains suggests that the crust of Io is essentially a layered stack of partially consolidated volcanic lavas and plume deposits, becoming more consolidated with depth. The lower crust especially may also be ductily deformed, punctuated by volcanic intrusions and faulting at paterae, and broken into blocks, some of which have been uplifted to form mountains.

(1) Solifluction-like lobes or small-scale lobes: well-defined lobe or tongue-shaped landform tens to hundreds of meters wide (Johnsson et al. 2012) (1.1) Non-sorted lobes or smooth-textured lobes. Small-scale lobes that show no evidence of a clast-rich lobe front (Johnsson et al. 2012; Fig. 1) (1.2) Sorted lobes or clast-banked lobes. Small-scale lobes that have a distinct front with clasts and relatively few clasts on the tread surface, similar to stone-banked lobes on Earth (Gallagher et al. 2011; Johnsson et al. 2012; Fig. 2)

At the shorelines of several lakes on Titan putative drowned river valleys are seen on radar images (Stofan et al. 2007). Flooded topography is indicative of very low slopes. This morphology suggests drowned coasts. A dendritic network of wide, km-scale valleys ending in Kraken Mare also shows ▶ ria morphology (see image in ▶Valley Network (Titan)). A submerged channel within a flooded valley and a nearby inundated crater form is suggestive of lower liquid levels in the past (Wasiak et al. 2013).

(1) Grounding line wedges or till deltas formed by the deformation of subglacial till (and other sediments) that reach the grounding line. These are fanor wedge-shaped sedimentary units. The mound’s top surface slopes slightly upward in the direction of flow, due to the pressure of the overlying ice shelf (Fig. 1). (2) Grounding line fans form where subglacial meltwater streams discharge subaquatically in a marine environment (Powell 1990). These are also named subaqueous esker deltas or beaded ▶ eskers (McMenamin and McGill 2005). (3) Morainal banks (moraine ridges, DeGeer moraines) formed by various processes, including pushing. They are often asymmetric, straight, or concave in planform.

(1.1) Knobs: small, typically rounded, isolated structures, often with steep slopes (isolated peaks) (Fig. 8/1) (1.2) “Mounds” may refer to any typically round-shaped elevation or may be understood as dome-like elevations. Subdued mounds are characterized by low-angle slopes. (1.2.1) Cones (conical mounds) have a circular to subcircular base that tapers to a (in many cases theoretical) point at the top (the apex – the peak), typically with concave or straight slopes (e.g., Fig. 4/14). (1.2.2) Domes (domical mounds) are circular to elliptical in plan view and have a smoothly rounded summit area and typically convex slopes (e.g., Figs. 1, 3/29, and 4/15). (1.2.3) Shield-like mounds are similar to cones or domes but with a wider base (lower height-to-diameter ratios) (e.g., Fig. 5/24). (1.2.4) Mesas (flat-topped mounds) have flat top and steep slopes and a circular to angular plan view shape. “Pancake-like structures” are usually understood as circular, compositional structures, whereas “mesas” are typically understood as eroded remnants of formerly larger structures. The term “flat-topped mound” has no genetic inferences. Sometimes they are called table mountains (e.g., Figs. 2/10 and 7/22, 31). (2) Raised rim depressions have “closed or mostly closed positive-elevation rims encircling lower elevation terrain” (Burr et al. 2009).