RIVER NIGER, THE OLDEST RIVER IN AFRICA WITH THE LARGEST DELTA IN THE WORLD.
SUBSURFACE MORPHOLOGY AND
BY SPACEBORNE AND AIRBORNE RADAR
BY SPACEBORNE AND AIRBORNE RADAR
Copyright ©1986 James J. Hurtak, Ph.D.
Los Gatos, CA 95031 USA
Los Gatos, CA 95031 USA
The shuttle imaging radar (SIR-A) carried on the Space Shuttle Columbia (November 1981) penetrated the dry Selima Sand Sheet, subsurface valleys and arid desert wastelands of the eastern Sahara, revealing previously unknown buried valleys and channels, unusual geologic structures, and possible Stone Age occupation sites, not detectable by Landsat. The calculated depth of radar penetration of dry sand and granules, based on laboratory measurements of the electrical properties of samples from the area extends, in some instances, to a depth of 6 meters. Field studies in Egypt verified SIR-A signal penetration depths of at least 1 meter in the Selima Sand Sheet and in drift sand and several meters in sand dunes. Subsurface findings at various locations from Kom Ombo to the Chad-Sudanese border suggests a massive paleo-drainage system that flowed in an west-east direction.
1. RADAR MAPPING
and Paleo-drainage in N. Africa:
and Paleo-drainage in N. Africa:
The presence of old drainage networks beneath the Selima Sand Sheet, dunes, and drift sand of the eastern Sahara provides a geologic explanation for the locations of many obscured playas and present day oases. This discovery originally made by SIR-A has revealed one of the major centers of episodic human habitation based upon a vast, now-vanished paIeo-drainage system. The existence of this drainage system is of paramount importance to the original continental framework of Northern Africa. The area of concern is the Arabian Desert that exists in the eastern Sahara. There are a few traces of gravel that were detected on the ground by Landsat, but prior to the SIR-A survey, no one had any appreciation of the true typology beneath the Sand Sheet and the dunes presently dominating this region.
The present Nile system runs along Egypt with its tributaries of the blue Nile and the white Nile, then over the crystalline rocks of the Red Sea Hills, the upper Arabian shield which is a zone of sea-floor spreading. (1) This spreading began in the late Neocene -- about 40 million years ago. In terms of the overall geomorphological picture this is a very important element, since it would indicate that this is a relatively active area. In addition near the border of the present Nile system there are various volcanic centers such as the Amhara Triangle in Ethiopia and the Tibesti Mountains in Chad. These are late Tertiary volcanic constructs which began with doming, followed by volcanism, sedimentation and the like.
1.1 Evidence in East Africa
In the midst of wind-eroded standstones in Chad, signatures of an ancient drainage system have been identified through SIR-B. Just south of the Libyan Desert area and east of the Tibesti Mountains, the bedrock formations of Devonian sandstone show varying resistance to erosion. Different image textures seen on SIR-B imagery of Northern Chad, indicate the presence of four sandstone units whose boundaries are marked by bedding scarps. Pronounced drainage channels can be seen between sandstone of very low relief, sand veneer and limited areas of outcrop. It is an area of flat terrain with a thin veneer of dry sand parallel to the dominant wind direction. The strike of the sandstone units is in the range direction. Gullies appear as extensive dark linear streaks that are nearly normal to the strike of the bedrock units and are in response to a lengthy period of wind erosion. (2) All these formations added to the greater picture of the ancient drainage channels have lead investigators to theorize the existence of a former wetter climate in this extremely arid region.
First seen by remote sensing, in the eastern Sahara there exists a large, very well expressed alluvial valley. In 1984, Ron Blom and colleagues carried on extensive fieldwork at the location of one of the Wadis (streambeds) in south central Egypt close to the Sudanese border. The purpose of their research was to verify and explain the topological findings from the SIR-A. Initial observations suggested a previous role of fluvial activity quite different from the present aeolian landscape.
One of the main research criteria was to demonstrate why the basin and valleys showed on radar such a great contrast from the surrounding terrain? Their research revealed great alluvial valleys that at one time carried large amounts of water, braided stream complexes and carved bedrock control channels. What Ron Blom and colleagues encountered, came to be called "radar river" systems. And on the south shore of one of the valleys out of this fluvial environment came a collection of early stone‑age artifacts, suggesting that Homo Erectus (early man) produced hand-axes about 250,000 years ago.
New vistas were gained into the character and significance of these valleys from diggings which showed there were massive areas of caliche sedimentary rock that was capable of being formed into nodules. This rock was extremely dense and covered by a very thin layer of sand sheet that is essentially transparent to the radar signal. The upper surface of this is quite rough at about the 10 cm scale. The sedimentary rock turned out to be the key to the braided stream channel complex. (3)
In some cases the signatures on the radar images show structural depressions and probable buried intrusives, as well as infiltration of bedrock crevices by windblown sand and collovium. This results in a dark response to SIR-A and has enhanced the patterns of these structures on radar images. In the soft area in the northeast corner of Sudan-Egypt a very complicated braided stream complex was discovered that gives rise to two important questions. Why do the islands appear as intermediate albedo on radar? And why do the channels which are there appear very dark? Extensive diggings were made within the channels via a series of trenches (set at five meter intervals) which revealed an inset channel system that also existed within the caliche (calcium carbonate). It was determined that the SIR-A radar was penetrating the uppermost sand layer, but scattering back part of the signal from these volume scatterers at a shallow depth. In effect, the dark response on the radar was going off somewhere else after reflecting off the interface and the signal and was not being recorded on the spacecraft.
The Sand Sheet is not a sand dune, but is a planar ubiquitous type of unit, the likes of which are not found anywhere in North America, nor in most of the deserts of the world. It is almost unique to this part of the Sahara and is organized into well-developed bed‑forms that have amplitudes no greater than a meter, such that when one scans the surface one cannot discern this relief. The wavelengths of this are 1/2 to 1 kilometer; they are extremely subtle forms with no slip faces. In addition to trying to establish the sedimentary environment, Blom and others had to work very hard to explain the radar physics and especially the caliche nodules along the walls of trenches in the crystal sand which is a massive fluvial unit. These nodules turned out to be of the right size and the right distribution to give an intermediate (radar) response after having the radar signal pass through the very thin upper unit of the aeolian sand sheet.
Direct on-site investigations further demonstrated the reality of these fluvial sediments, showing that they are not simply an anomaly of the radar imaging system. A large series of trenches, 2 to 3 meters deep and 10 meters wide were constructed. (4) In the walls of these trenches, sand sheet was found on top with other loose material -- and beneath petrogenesized older sand sheet (brick-like in character), was an aeolian nonconformity covering an alluvial sequence. There was found all the earmarks of deposition in a fluvial environment. For instance, in the deposits were gathered examples of fresh‑watered mollusks, one of which is a biofulariaflyferide which is a species that can live only in stony fresh-water environments, along the banks of fresh‑water streams supporting vegetation.
Researchers at the site have brought up to the surface several hundred meters of geological strata from below. They also incorporated in their findings the seismic work done by German engineers that showed a large difference in velocities (between 350 to 800 feet per second in the upper unconsolidated and 1100 to 1500 feet in the consolidated below). The bedrock stretches from 4500 to 5600 seismic velocities -- thereby showing density effects velocity providing the bedrock is of different density.
The geological samples gave remarkable cross-sectional evidence of a fill area changing somewhere between the Tertiary and Pleistocene epoch when aridity began to set into the Sahara about 2 million years ago. The streams changed from earlier cycles of humid environmental characteristics, from tropical conditions in the Neocene and the Oligocene to the later Miocene and eventually to the semi-arid conditions beginning probably in the Pliocene end of the Tertiary period.
Fluvial activity may have continued into the Quaternary period which is known to have a number of fluvial periods, theorized by some to have taken place: 8,000, 50,000, and a major fluvial period 300,000 years ago. Each fluvial activity appears to correspond to a major period of human occupation in the area.
Evidences gathered from regional considerations, from a series of excavations in the Wadis that were explored and some of the larger alluvial valleys were sufficient to create a model of what one of these "radar rivers" looked like. (5) The major sources used to create the model were from the geophysical information pertaining to the depth of the various strata, the alluvial sequences and information from the velocities of the various strata supplied by the General Petroleum Company (of Egypt) seismic team. Researchers, Ron Blom and colleagues, have deduced that at some early Tertiary period of earth's history the environment in this region was humid, with massive streams flowing throughout southern Egypt at a period even before the course of the Nile River as we know it today.
1.2 Radar Implications in Egypt
We have a model for early fluvial activity in the region of northern Africa, but we are still faced with a major question of where did these rivers come from? The exciting implications are as follows: The mid-Tertiary period data along with the SIR-A and SIR-B data put together with all the known drainage lines in this area seems to indicate that the drainage was generally from East to West, during the Tertiary Period. Various confluent rivers and streams are suspected of flowing off what was at that time some of the highest points of North Africa, namely the Red Sea Hills. The flow was across the waistline of Africa toward Lake Chad, before the Tibesti, Darfur and Ethiopian highlands were formed. If these volcanic constructs and rift zones were not there - the rivers, given sufficient drainage from the Red Sea mountains would not have stopped, but may have gone all the way to the Atlantic.
In Figure 1 we see the pattern of the present day drainage in North Africa and the general direction of river patterns as they may have looked in the Tertiary Period The Nile system at the very earliest of its beginnings is thought to have occurred at a time when the Mediterranean dried up - about the late Miocene - 6 million years ago. This would have been the beginning of the Nile, due to an activity which cut a canyon from the vicinity of Cairo all the way back to Aswan with an equivalent depth of the Grand Canyon, but three times as long. The effect of this on the earlier drainage system (early Tertiary period) would be to behead the trans-African streams that were discovered by means of SIR-A radar and formerly unknown. It would have cut off this ancient river system from their head-water. This Nile complex, however, does not appear to have been fully integrated with the head waters until 12-24,000 years ago.
Thus the young and relatively unstable Nile is superimposed as a pirate stream on what appears to be an older drainage system that goes horizontal across North Africa. On the other side of the continent there is the well active Chad drainage (near the Benue complex). Lake Chad was part of a larger system which even today overspills by way of numerous river routes, e.g., into the Benue, a tributary of the Niger River reaching the Niger Delta and the Gulf of Guinea.
NIGER @ SUNRISE.
The Niger Delta is the largest delta of any river in the world (it is something on the order of 3 to 4 times larger than the Nile delta). This is most unusual. Researchers are now questioning whether the rivers connected with the Niger Delta are vast enough to have given enough water to create this large of a delta. A view of Northern Africa in mid-Tertiary times -- some 25-30 million years ago - according to this research would show a much greater trans-African drainage system. This drainage system could easily account for the vastness of the delta system -- a river system which spanned from east Africa to Nigeria, later beheaded by the Nile growing southward.
All this information has been brought to light by radar contributions in this area -- using both SIR-A and SIR-B -- which provided information of the missing links -- and stimulated first‑hand field investigations. From the vantage point of radar observation, this river system is still extant even though only the western portion is operational.
SIR-A showing Paleo-drainage in North Africa
According to Dr. Geoft Lawrence, SIR-B uncovered quaternary sand and gravel deposits over wide areas and long linear dunes in the western desert areas of Egypt extending in a north-south direction. (6) This would imply that the course of the waterflow did begin to change probably as early as the Pleistocene epoch. The scarp of the Gebel area (by the Egyptian-Sudanese western frontier) appears bright in the SIR-B images, whereas large rock pediments in front of the scarps may be partly covered by radar-transparent sand which appears in moderately bright tones on the images. This is in contrast to thicker sand sheets in the interdunal areas which appear in darker tones. It was found that dune surfaces yield radar backscatter only when the radar incidence angle is less than the angle of repose of the dune slopes.
When one looks at the mega-morphology - one sees that the extensiveness of this ancient river drainage system was of the magnitude what we find today in the Amazon. Indisputably today's greatest river in the world, the Amazon drains a basin that covers 40 per cent of South America and covers an area of over 5.8 million square kilometers. (7) The Amazon's watershed is drawn partly from the Andes, the width of a continent away.
In fact, Africa and South America separated in the late Tertiary Period when the South Atlantic opened. If one entertains the size of the Niger Delta, the largest delta in the world, the Benue system, the Mandara system, and interfaces these with its counterpart where the vast complex of Amazonian waterways connect with the Atlantic estuary, an enormous parallel of a drainage complex emerges.
It is important to understand the theoretical length and volume of this trans-African system in comparison with the world's present river systems.
TABLE 1: Comparison of World's Largest River Systems with the Trans-Africa (Trans-A) Radar River
In terms of tectonics, the doming of the Afro-Arabian shield took place creating the trailing edge and the regional slopes of the African continent over a time period on the order of 20 million years -- which is four times longer than the oldest recognizable segments of the Nile. The new subsurface findings from SIR-A and SIR-B suggest a complex pattern of swamp, dark lakes, and black threads of waterways connecting paleo-drainages across the waistline of Africa, providing missing links between earlier watershed areas and the enormous delta of Niger. Drilling in this area indicates the present sedimentation formed mainly in the very late Neocene.
In summary, our research indicates that the trans-African drainage system is like a mirror image of the Amazon system and of comparable age to the Amazon. The demise of such a trans-African system in the Pleistocene Epoch can be traced to three causes: 1) the beheading influences on the waterways; 2) the rise of the volcanic areas around central Africa which disrupted the drainage system and, in turn, created a dam complex and a large area of sedimentation on the back side of the volcanoes; and 3) the massive event that finally killed the system was a period of large scale dedication after which the trans-African system was put on a downhill course ever since in leaving Africa drier and drier.
In addition to the region of south central Egypt where the majority of research took place. SIR-B also uncovered various other features in Northern Africa which has lead investigators to a greater understanding of the geological structures in this area. SIR-B over northeast Sudan has been the identification of a major suture line, called the 35 degree east suture, where an island arc assemblage of volcanic and sedimentary rocks was destroyed during the Late Precambrian period. Recent geo-dynamic studies suggest that the 35-degree east suture was an antecedent of faults associated with the fragmentation of the Nubian/Arabian Shield and the opening of the Red Sea. (8) The radar images expressing small‑scale textural differences would suggest that the origin of the Nile complex is to be found in the west rather than the south.
2. Complimentary Technology for Geo-archaeology
The concept of spaceborne imaging radar was proven by SEASAT, LANDSAT, SIR-A, and SIR-B, extensively utilizing it in the fields of oceanography and geology where the data retrieved proved to be extremely interesting to geologists and energy specialists. This data has been used to discriminate other types of terrain, locating oil shale, limestone and minerals. SAR does have limitations, yet they don't coincide with the limitations of conventional prospecting techniques. Consequently, integration of the SAR-technology with proper image enhancement techniques and sonar can greatly improve the accuracy level in any project evaluation.
Spaceborne imaging radar sometimes requires complimentary information in the thermal infrared region of the electromagnetic spectrum. IR laser and spectrometer technologies provide enough information so that potential investigators can decide whether or not advanced cross-track scanning is needed in their research program. Visible, reflected IR, and thermal IR measurements are perturbed to a significant degree by atmospheric effects. Thus the attenuation and scattering characteristics of the atmosphere at the times and locations of the observations must be known as a function of wavelength to remove the atmospheric effects from the signals. (9)
In conclusion, many lessons have been learned over the last ten years about the historical nature of large, complex drainage systems. A well-structured approach is afforded by airborne and space borne radar observations. Through this man/machine interface water conduits, energy recourses, and a complete observation of the entire bio-system in its historical context can be understood.
This system of remote sensing covers a wide range of surface and substructure enhancements. Since the investigation of relevant drainage basins is time-consuming, remote sensing of these systems can give us an integrated understanding of the spatial distribution of vegetation cover, soil type, soil moisture content, ground surface temperature, subsurface water occurrence, and so on over the entire drainage area.
Remote sensing requires a state-of-the-art multiple computer redundancy management concepts, incorporating a multitude of functions to support operations on the ground and in flight. Added to this are considerations and efforts of hundreds of engineers participating in the development, verification, utilization, and support of SIR-A, SIR-B and CV-990 programs in unique energy-related, environmental tasks.
Analysis of co-registration of all SAR images reveals that the radar image data can make a several percentage contribution in rock-type discrimination over LANDSAT and Brasilian RADAM data alone. Incorporation of textural measure from the radar images greatly increases their values and results in an additional 14-percent gain in discrimination ability. Other texture measures found very useful are hue saturation-intensity split spectrum processing, Fourier band-pass filtering, and SPIT processing. The additional dimension of color or the summation of gray values added to the radar image is a potentially powerful image-enhancement tool.
The complexity of the interrelationships and interdependence between various components of drainage hydrology and geomorphology require a multi-systems approach since the subsequent movement of water from the head -waters to its outlet change the structure of the system itself and result in an output from the source not only of water but also of water-borne material in the form of dissolved, suspended, and bed load. In the same way the individual hydrologic processes operating within the drainage basin, e.g., precipitation, interception, evapor -transpiration, soil moisture, and groundwater movement and storage, and the runoff process itself, must be applied on many levels if numerical solutions are to be obtained. Here SAR provides for the synthetic eye for viewing the changing spatial patterns and relationships of terrestrial phenomena viewed as the world of man.
Various geologic applications of radar images may be significantly aided through the use of the methods discussed in this paper such as the SPIT process. It is hoped that these additional methods coupled with SAP and LAS (etc.) will provide great benefits in exploring the energy picture in the 21st Century. It appears that the chief observational contributions will come from seismology, isotopic studies, optical and digital radar systems. Low altitude spacecraft have a strong contribution to make in the global, synoptic measurements of potential fields. In addition, to spatial information, measurements of the global secular variation of the magnetic field is also required.
Most importantly, with this new technology in hand, distance measurements from space shout also contribute to a detection of new energy resources, the monitoring of renewable and nonrenewable sources, and the global cooperation that will be needed in the sharing of high technology for both the energy needs and the ecological balance of the planet. (10)
Consequently, if we ask the right question and if we collect the appropriate data of sufficient accuracy in a timely fashion, these experiments should give us major new insights into many of the energy alternatives needed to address the major problems of the future integrity of our global habitat.
Appendix A: Other Spectral Areas
An overview of the various bands are as follows: P band uses longer wave signals; the frequency is proportional to the reciprocal of the wavelength -- so, L-band is 1000 to 1300 megahertz, and this is 3/10 of a meter. X-band is 10,000 megahertz, or 3 centimeters. C band is 5 Gigahertz and turns out to be 15 centimeters. 450 megahertz is below the cellular radio (on earth). Its about 3/4ths of a meter -- 70 centimeters. The longer the wavelength, the better chance of getting deeper penetration on the order of (conductivity, etc.) proportional to the wavelength. In fact, snow can be penetrated with the X-band.
Appendix B: Computer Futures with Remote Sensing
Additional information on coupling interface priorities between airborne equipment and processing tools:
1) Coding of some of the necessary algorithms with a fixed point design has proved to be somewhat costly in terms of computer time and memory. Future machines should include hardware floating-point arithmetic with sufficient precision.
2) Spacecraft requirements seem to demand continued increases in on-board autonomy and control system performance, i.e., new computers operating at higher speeds & contain more memory.
3) Use of nonvolatile memory technology, such as core or plated wire, has proved almost essential. It can be power-strobbed and therefore expanded with little increase in power. It is immune to radiation and retains its content when power is removed from the computer, either on purpose or by some anomaly. New space computer designs should, as a minimum, use nonvolatile technology for the program portion of memory.
4) In general, science data processing and micro-control of mission instruments using the central computer should be avoided and proper instrumentation should be brought in. Microprocessors within the instruments can best perform these tasks.
5) An extensive software development and test system that has a high fidelity simulation of the computer's environment is valuable in uncovering timing and logic problems
1. Sea-Floor spreading proposed in the early 1960's by the American geologists Harry Hess and Robert Dietz.
2. Ford, John P., et al, Shuttle Imagining Radar Views Earth From Challenger: The SIR‑-B Experiment, NASA, 3/15/1986, p. 56.
3. "Caliche" deposits were found formed by a high evaporation of calcium carbonate water. This material was found as rough, irregularly formed bodies, not consolidated enough to be in the form of Travertine.
4. Pioneering work is being done by Dr. John McCauley (USGC) & colleagues revisiting/ excavating SIR-A lines in Egypt-Chad, etc. Ground survey work by Dr. Hurtak and associates, 1983.
5. "Calcrete cementation" structures were found intertwined with radar rivers. Radar rivers were formulated on the basis of subsurface features which appeared as anomalies via SIR-A. Here Calcrete (from "calcium carbonate" and "hard layer") is identified with Caliche materials, resulting from the binding of sedimentation rock by calcium minerals.
6. Notes from Dr. Geoft Lawrence, Hunting Geology and Geophysics, Ltd., to Dr. John Ford, JPL., 1986.
7. Vital statistics in Great Rivers of the World, National Geographic Society, Washington, D.C. 4th Annual Earth Resources Program Review. National Oceanic and Atmospheric Administration Programs and U.S. Naval Research Lab. Programs. Houston, Texas, 1972.
8. Personal discussions with Dr. Mel Stinson and others and the University of California working on geo-dynamic models of continental drift and Gondwanaland.
9. ABRAMS, MICHAEL J. and KAHLE, ANNE B. "Recent developments in lithologic mapping using remote sensing data,"Proceedings of the IUGS-UNESCO Program on Geological Applications of Remote Sensing, Seminar on Remote Sensing for Geological Mapping, Orleans, France, February 2‑4, 1984.
10. NASA's objectives for the future include: 1) Landsat TM coverage over lard completed & available. Work done on using multi-spectral data to map rock mineral assemblages. 2) SIR-B; SIR-C flown and multi-incidence angle capability utilized to characterize roughness. Some X-band and L-band data acquired simultaneously. 3) Large format camera data analyzed with new image enhancement for selected areas. 4) Progress made on physical basis for utilizing vegetation to map soil-bedrock characteristics and to locate fossil fuels. 5) Some high resolution multi-spectral imaging in reflected & emission part of spectrum, from low Earth-orbit system shuttle.