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African landscape evolution since 66 Ma reflects interactions among parts of the Earth system from the Core to the Biosphere. We stress changes in those interactions in three events that have dominated landscape development: (i) a climatic revolution when the circumpolar current and the East Antarctic ice sheet first formed ∼37 Ma; (ii) a tectonic revolution at ∼32 Ma dominated by elevation of ∼30 topographic structural swells continent-wide; and (iii) a second climatic revolution in a Northern Hemisphere cooling event (at ∼2.7 Ma) that triggered Sahara desert initiation and the beginning of glacial cycles in the Northern Hemisphere (∼2.15 Ma). We recognize the following distinct features of the great Afro-Arabian continent (∼40 M km2) that show its relationship to Earth structure and processes: deep mantle structure and dynamics, plate motion with respect to that structure, especially plate-arrest (∼32 Ma). The topographic, erosional, geomorphic, and depositional modifications following that tectonic event were strongly influenced by changes around the continent in oceanic and atmospheric circulation that affected the entire continent. Atmospheric circulation changes since ∼34 Ma have involved zonal winds, the ITCZ, desert formation and destruction, the evolution of the persistent (since ∼35 Ma) Antarctic ice sheet, and since ∼2 Ma of the rapidly cycling Eurasian ice sheets. We explain that a widely supported idea that ancient erosion surfaces have survived at high elevations in Africa is the result of a failure to recognize that the present elevations of the continent’s swells are dynamically maintained, but do not display a thermochronological signature because they are young (less than ∼32 My), so that conduction of heat from shallow convection cells has not yet reached the Earth’s surface.

A global study of megafans (greater than 100 km long) has revealed their widespread existence on all continents, with almost 200 documented, 93 in Africa where research is most thorough. The largest measures 705 km. Megafans are a major subset of "DFS" (distributive fluvial systems, a category that includes all fan-like features greater than 30 km long). 1. Many researchers now recognize megafans as different from floodplains, small coarse-grained alluvial fans, and deltas. Although smaller architectural elements in megafans are the same as those encountered in floodplains (channel, overbank, etc.), larger architectures differ because of the unconfined setting of megafans, versus the valley-confined setting of floodplains. 2. A length continuum is now documented between steep alluvial fans 10-20 km in length, and fluvial fans 30-50 km long. This implies a continuum of process from end-member alluvial fan processes (e.g. high-energy flows that emplace gravels, debris-flow units) to the relatively fine-grained channel and overbank deposits common to purely fluvial fans. Combinations of these different processes will then occur in many mid-sized fans. 3. The global distribution suggests a prima facie relationship with tectonic environment rather than climatic zones, with local controls being the slope of the formative river and the existence of a basin subsiding below the long profile of the river. But the global population has revealed that most megafans are relict. So it is possible that further research will show relationships to prior climatic regimes. 4. Megafans can have regional importance: e.g., along the east flank of the central Andes, nested megafans total approximately 750,000 km2-and 1.2m km2 if all megafans in S. America are counted. Modern megafan landscapes thus have basinal importance, orders of magnitude greater than alluvial fan bajadas. 5. Because so many aggrading basins are dominated today by DFS, it is claimed that DFS ought to be significant in the subsurface; and that existing fluvial models therefore may not apply to the majority of fluvial sedimentary units. Arguments have been raised against this view, but as modern megafan systems become better known they are rapidly being applied as a model in many fluvial basins. A small literature has arisen with apparent examples from every part of the world.

Megafans are partial cones of river sediment usually laid down by a single switching river, characterized by areas on the order of 103–105 km2, smooth plains, and slopes of

(1996). Earth observations during space shuttle mission sts‐69 Endeavour's Images of Earth (September 7–18, 1995) Geocarto International: Vol. 11, No. 1, pp. 91-104.

A description is presented of the activities and results of the Space Shuttle mission STS-45, known as the Mission to Planet Earth. Observations of Mount St. Helens, Manila Bay and Mt. Pinatubo, the Great Salt Lake, the Aral Sea, and the Siberian cities of Troitsk and Kuybyshev are examined. The geological features and effects of human activity seen in photographs of these areas are pointed out.

An overview of space flight STS-41 is presented, including personal observations and comments by the mission astronauts. The crew deployed the Ulysses spacecraft to study the polar regions of the sun and the interplanetary space above the poles. Environmental observations, including those of Lake Turkana, Lake Chad, biomass burning in Madagascar and Argentina, and circular features in Yucatan are described. Observations that include landforms and geology, continental sedimentation, desert landscapes, and river morphology are discussed.

An overview is presented of photographs, astronaut impressions, and photographic equipment and techniques coincident with the Discovery STS-33 mission of November 23-27, 1989. Particularly significant geographical photographs of southern Africa, Madagascar, northern Africa, Southeast Asia islands, Pacific islands, and Australia are shown and reviewed. Meteorological and oceanographic observations are summarized along with film anomalies that occurred during this mission.

An overview is presented of the 31st Space Shuttle mission, whose major objective was to deploy the Galileo spacecraft. Color images are presented of photos taken by the four videocameras in the payload bay, one 16-mm Arriflex in the cabin, a videocamcorder, three 35 mm cameras, two 70 mm cameras, and an IMAX camera. In addition, descriptions of visual observations by the mission astronauts are given. The most significant STS-34 earth photography for the major geographical regions is discussed. Individual highlights of this mission include observation of the apparent recovery of the water level of Lake Nasser to conditions similar to those during the second Space Shuttle mission of 1981; the documentation of the impact of the Yucatan forest blowdown and fires after the passage of Hurricane Gilbert; and the confirmation of the high value of space photography under low and very low sun angle conditions for geomorphological and geological analyses.