ABSTRACT The Ice Age National Scenic Trail leads hikers on a 1200-mi (1900-km) tour of glacial and other geologic features across the State of Wisconsin. This one-day field trip highlights glacial landforms of the Superior Lobe of the southern Laurentide Ice Sheet in northwestern Wisconsin. Here the Ice Age Trail features spectacular end moraines, low-relief and high-relief hummocky topography, ice-walled-lake plains, eskers, tunnel channels, striations, and water-scoured features on basalt. The field trip involves several short hikes on parts of the trail, including one on a classic esker located in a tunnel channel. We argue that there is paleoglaciological significance to differing landform assemblages on the older, low-relief Emerald Phase land surface and the younger St. Croix Phase moraine, which has numerous high-relief hummocks, ice-walled-lake plains, and tunnel channels. Large potholes from the drainage of glacial Lake Superior are present at the Interstate State Park Unit of the Ice Age National Scientific Reserve.

Conventional interpretations assign Venus a volcanotectonic surface, younger than 1 Ga, pocked only by 1000 small impact craters. These craters, however, are superimposed on a landscape widely saturated with thousands of older, and variably modified, small to giant circular structures, which typically are rimmed depressions with the morphology expected for impact origins. Conventional analyses assign to a fraction of the most distinct old structures origins by plumes, diapirs, and other endogenic processes, and ignore the rest. The old structures have no analogues, in their venusian consensus endogenic terms, on Earth or elsewhere in the solar system, and are here argued to be of impact origin instead. The 1000 undisputed young “pristine” craters (a misnomer, for more than half of them are substantially modified) share with many of the old structures impact-diagnostic circular rims that enclose basins and that are surrounded by radial aprons of debris-flow ejecta, but conventional analyses explain the impact-compatible morphology of the old structures as coincidental products of endogenic uplifts complicated by magmatism. A continuum of increasing degradation, burial, and superposition connects the younger and truly pristine young impact structures with the most modified of the ancient structures. Younger craters of the ancient family are superimposed on older ones in impact-definitive cookie-cutter bites and are not deflected as required by endogenic conjectures. Four of the best-preserved of the pre-“pristine” circular structures are huge, with rimcrests 800–2000 km in diameter, and if indeed of impact origin, must have formed, by analogy with lunar dating, no later than 3.8 Ga. Much of the venusian plains is seen in topography to be saturated with overlapping 100–600 km circular structures, almost all of which are disregarded in conventional accounts. Several dozen larger ancient plains basins reach 2500 km in diameter, are themselves saturated with midsize impact structures, and may date back even to 4.4 Ga. Giant viscously spread “tessera plateaus” of impact melt also reach 2500 km in diameter; the youngest are little modified and are comparable in age, as calibrated by superimposed “pristine” impact structures, to the least modified of the giant impact basins, but the oldest are greatly modified and bombarded. The broad, low “volcanoes” of Venus formed within some of the larger of the ancient rimmed structures, resemble no modern volcanic complexes on Earth, and may be products of the collapse and spread of impact-fluidized central uplifts. Venusian plains are saturated with impact structures formed as transient-ocean sediments were deposited. The variable burial of, and compaction into, old craters by plains fill is incompatible with the popular contrary inference of flood basalt plains. Early “pristine” craters were formed in water-saturated sediments, subsequent greenhouse desiccation of which produced regional cracking and wrinkling of the plains and superabundant mud volcanoes (“shields”). The minimal internal planetary mobility indicated by this analysis is compatible with geophysical evidence. The history of the surface of Venus resembles that of Mars, not Earth.

A systematic pattern of beach ridges forming strandplains commonly fills embayments in the Great Lakes of North America. Ground penetrating radar (GPR) and vibracore results define a common preserved architecture inside beach ridges. Comparing the preserved architecture with a conceptual model of beach-ridge development explains the conditions responsible for their development and preservation. Great Lakes beach ridges are a product of a positive rate of sediment supply and a multidecadal fluctuation in lake level. Many shoreline behaviors occur throughout the development of a beach ridge, but not all successions originally formed by these behaviors are preserved. Beach ridges are stratigraphically separated by concave lakeward-dipping ravinement surfaces extending at depth below beach-ridge crests to the ground surface in adjacent landward swales. These surfaces are formed during rapid rises in water level, where previously laid deposits erode, forming a base for the beach-ridge core. As the rate of rise decreases and the water-level elevation approaches a highstand, the core of the ridge is built by vertical aggradation. Subsequent deposits build lakeward during progradation when water levels become stable, protecting the core from being eroded during future rapid rises in water level. Dune sand deposits on beach-ridge cores are stabilized by vegetation, and swales are commonly filled with organic material.

The Western Escarpment of the Andes at 18.30°S (Arica area, northern Chile) is a classical example for a transient state in landscape evolution. This part of the Andes is characterized by the presence of >10,000 km 2 plains that formed between the Miocene and the present, and >1500 m deeply incised valleys. Although processes in these valleys scale the rates of landscape evolution, determinations of ages of incision, and more importantly, interpretations of possible controls on valley formation have been controversial. This paper uses morphometric data and observations, stratigraphic information, and estimates of sediment yields for the time interval between ca. 7.5 Ma and present to illustrate that the formation of these valleys was driven by two probably unrelated components. The first component is a phase of base-level lowering with magnitudes of∼300–500 m in the Coastal Cordillera. This period of base-level change in the Arica area, that started at ca. 7.5 Ma according to stratigraphic data, caused the trunk streams to dissect headward into the plains. The headward erosion interpretation is based on the presence of well-defined knickzones in stream profiles and the decrease in valley widths from the coast toward these knickzones. The second component is a change in paleoclimate. This interpretation is based on (1) the increase in the size of the largest alluvial boulders (from dm to m scale) with distal sources during the last 7.5 m.y., and (2) the calculated increase in minimum fluvial incision rates of ∼0.2 mm/yr between ca. 7.5 Ma and 3 Ma to ∼0.3 mm/yr subsequently. These trends suggest an increase in effective water discharge for systems sourced in the Western Cordillera (distal source). During the same time, however, valleys with headwaters in the coastal region (local source) lack any evidence of fluvial incision. This implies that the Coastal Cordillera became hyperarid sometime after 7.5 Ma. Furthermore, between 7.5 Ma and present, the sediment yields have been consistently higher in the catchments with distal sources (∼15 m/m.y.) than in the headwaters of rivers with local sources (<7 m/m.y.). The positive correlation between sediment yields and the altitude of the headwaters (distal versus local sources) seems to reflect the effect of orographic precipitation on surface erosion. It appears that base-level change in the coastal region, in combination with an increase in the orographic effect of precipitation, has controlled the topographic evolution of the northern Chilean Andes.