Responses of floods to Holocene climatic change in the upper Mississippi Valley

Dimensions of Holocene relict channels and sedimentological characteristics of point bars associated with these relict channels were used to reconstruct a Holocene history of long-term changes in magnitudes of 1.58-yr floods in Upper Mississippi Valley watersheds of southwestern Wisconsin. The reconstructed record of floods shows relatively large and persistent (nonrandom) departures from contemporary long-term average flood magnitudes. The flood history indicates climatic changes that are broadly similar to climatic changes indicated from fossil pollen in the same region. The Holocene floods ranged from about 10–15% larger to 20–30% smaller than contemporary floods of the same recurrence frequency. Large floods were characteristic between about 6000 – 4500 and 3000 – 2000 yr B.P., and during a brief interval after 1200 yr B.P. Small floods were common between about 8000 – 6500, 4500 – 3000, and 2000 – 1200 yr B.P. These fluvial responses were found to be closely associated with a long-term episodic mobility and storage of sediments in the Wisconsin watersheds. During periods of relatively large floods, relatively rapid lateral channel migration either reworked or removed extensive tracts of valley bottom alluvium. In contrast, during periods of relatively small floods, relatively slow lateral channel migration is apparent and the channel and floodplain system appear to have been relatively stable.     

Examining the case for the use of the Tertiary as a formal period or informal unit

The ‘Tertiary’, omitted from IUGS-approved timescales since 1989, is still in common use. With the recent re-instatement of the Quaternary as a formal unit, the question arises as to whether the Tertiary too should be reinstated as a formal period, with the ‘Paleogene’ and ‘Neogene’ being downgraded to sub-periods. This paper presents arguments for and against this proposal, stemming from discussions by members of the Geological Society Stratigraphy Commission. It is intended to stimulate discussion of the topic in the wider community.     

Characterization of the near-Earth Asteroid 2002 NY40

In August 2002, the near-Earth Asteroid 2002 NY₄₀, made its closest approach to the Earth. This provided an opportunity to study a near-Earth asteroid with a variety of instruments. Several of the telescopes at the Maui Space Surveillance System were trained at the asteroid and collected adaptive optics images, photometry and spectroscopy. Analysis of the imagery reveals the asteroid is triangular shaped with significant self-shadowing. The photometry reveals a 20-h period and the spectroscopy shows that the asteroid is a Q-type.     

Vorticity in the magnetosphere

It is shown that Birkeland current and vorticity in the magnetosphere are intimately related, suggesting the importance of taking explicit account of vorticity, particularly velocity shear, when considering magnetospheric motions. An equation of motion for the magnetosphere coupled to the ionosphere is derived. It is suggested that experience with MHD fluids generally might fruitfully be brought to bear on certain problems in the magnetosphere to answer the question, not ‘why a sheet of Birkeland current,’ but rather ‘why a localised velocity shear.’     

Pharaonic necrostratigraphy: a review of geological and archaeological studies in the Theban Necropolis, Luxor, West Bank, Egypt

We present a review of archaeological and geological studies on the West Bank as a basis for discussing the geological setting of the tombs and geologically related problems with a view to providing archaeologists with a framework in which to conduct their investigations on the restoration, preservation and management of the antique monuments. Whereas the geology of the Upper Nile Valley appears to be deceptively simple, the lithological succession is vertically variable, and we have recognized and defined several new lithological units within the upper Esna Shale Formation. We have been able to delineate lithological (shale/limestone) contacts in several tombs and observed that the main chambers in some were excavated below the Esna Shale in the Tarawan Chalk Formation. We have been able to document changing dip in the strata (warping) in several tombs, and to delineate two major orientations of fractures in the field. Investigations behind the Temple of Hatshepsut, in the Valley of the Kings and around Deir El Medina have revealed four broad regional structures. We confirm that the hills located near the Nile Valley, such as Sheik Abdel Qurna, do not belong to the tabular structure of the Theban Mountain, but are discrete displaced blocks including the Thebes Limestone, as supported by Google Earth photographs.     

Floodplain sedimentation in the Upper Mississippi Valley: Natural versus human accelerated

Understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology. Floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters, and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems. Here, ¹⁴C and ¹³⁷Cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper Mississippi River and adjacent tributaries in southwestern Wisconsin and northwestern Illinois. The most important environmental change that influenced fluvial activity in this region during last 10,000 years involved the conversion of a late Holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with Euro-American settlement. Results presented herein for the Upper Mississippi Valley (UMV) show that the shift from pre-agriculture, natural land cover to landscape dominance by agricultural land use of the last 175–200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude. Accelerated overbank flooding led to increased bank heights on tributary streams and, in turn, contributed to more frequent deep flows of high energy. These high energy flows subsequently promoted bank erosion and lateral channel migration, and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain. The new historical floodplain serves as a “flume-like” channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods. Floodplains on lower tributaries, however, continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950. This lower valley anomaly is explained by minimal development of historical (agriculture period) meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient. In general, long-term pre-agriculture rates of vertical accretion between about 10,000 and 200 years ago averaged about 0.2 mm yr^− 1 in tributary watersheds smaller than about 700 km² and about 0.9 mm yr^− 1 on the floodplain of the upper Mississippi River where the contributing watershed area increases to about 170,000 km². On the other hand, rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr^− 1, with short episodes of even higher rates during times of particularly poor land conservation practices. Significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid-19th century. The hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture. High resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper Mississippi River. The relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper Mississippi River should experience increased frequencies of extreme hydrologic events, including large floods, with anticipated continued global warming. Instrumental and stratigraphic records show that, coincident with global warming, a shift to more frequent large floods occurred since 1950 on the upper Mississippi River, and these floods generally contributed high magnitudes of floodplain sedimentation.     

The geography of medical care delivery: an historical perspective

A weakness of research into urban service delivery has been its ahistorical approach. Historical geographers, on the other hand, have neglected the issue of urban service delivery. This paper illustrates the influence and interaction of urbanization, professionalization and public policy on urban service delivery using the example of medical care in Britain.     

Tetracyclic diterpenoid hydrocarbons in some Australian coals,sediments and crude oils

Tetracyclic diterpenoid hydrocarbons (diterpanes) based on the ent-beyerane, phyllocladane and ent-kaurane skeletons have been identified in the hydrocarbon extracts of some Australian coals, sediments and crude oils. Structures were assigned to the geological diterpanes by comparison with synthetically prepared reference compounds. Studies of a sample suite consisting of low-rank coals and sediments indicate that the ratios of C-16 epimers of phyllocladane and ent-kaurane are maturity dependent, and that the relative proportion of the thermodynamically preferred 16β (H)-compounds increases with increasing thermal maturity. Thermodynamic equilibrium for the interconversion reactions is attained in sediments before the onset of crude oil generation.The most likely natural product precursors for the tetracyclic diterpanes are considered to be the tetracyclic diterpene hydrocarbons which occur widely in the leaf resins of conifers. Tetracyclic diterpanes have been identified in sediments and coals of Permian age or younger, suggesting that these compounds are markers for both modern and extinct families of conifers. In particular, phyllocladane is proposed as a marker for the Podocarpaceae family of conifers.