Numerical simulations using the Penn State University/NCAR MM4 model are performed to examine a stably stratified, zonal easterly flow past large scale three-dimensional mountain ranges in a rotating, initially barotropic, atmosphere. Upstream blocking by the mountain range diverts the flow primarily to the south and around the mountain. Conservation of potential vorticity results in the formation of a horizontal jet at low levels south of the mountain. This jet is barotropically unstable and leads to a continuous production of synoptic scale vorticity maxima which separate from the mountain and propagate downstream. Numerical simulations using topography representative of the Sierra Madre in Mexico imply that this mechanism may be important in providing some of the initial disturbances which grow into tropical cyclones in the eastern North Pacific Ocean. The wave train produced in the simulations corresponds to waves with 3-7 day periods which have been identified observationally in the eastern North Pacific region. The sensitivity of this effect to the stability of the basic state and the upstream wind speed is investigated. Simulations are also performed which show that the Hoggar and Atlas mountains of west-central Africa block the low-level easterlies resulting in a barotropically unstable jet and a train of vorticity maxima which separate from the mountain and propagate downstream. The spacing of these disturbances is roughly 1600 km and they propagate to the east with a period of about 2.5 days. These characteristics correspond to those of observed waves in the Africa/Atlantic region. It will also be shown that the unique topography of north-central Africa results in a mid-tropospheric easterly jet which has a maximum between 0-10°E and 15-20°N. The location and magnitude of this jet correspond to the so-called African easterly jet which is usually attributed to the strong surface temperature gradients over the continent of Africa. The numerical simulations presented in this work suggest that the mechanical effect of the topography may provide a constant source of energy for the maintenance of the African easterly jet.

The subject of this work is the concern for the public enjoyment of the open countryside in England and Wales which grew up between 1919 and 1939. I have attempted to analyse its constituent parts, assess their influence and judge their longer-term significance. Its scope has been limited to the political and social sphere and is primarily an examination of the inter-play between public opinion and various interest groups on the one hand and the process of parliamentary and governmental decision-making on the other. In broad terms the study falls into two parts. One is the campaign for the establishment of National Parks between 1925 and 1939 and the other the campaign for the enactment of the Access to Mountains Bill which can be traced through the whole twenty-year period, and indeed from much earlier. Within the first part attention is concentrated on the work of the Addison Committee on National Parks (1929-1931), subsequent parliamentary and public interest in its recommendations and upon the work of the Standing Committee on National Parks, which was set up in 1935. The Access campaign is first considered in general terms by looking at the development of walking as a popular open-air pastime and the struggle for public access to the moorlands in the Peak District, and then a more detailed scrutiny is made of the events leading up to the passing of the Access to Mountains Act of 1939. As little material has yet been published on this subject the source material used has in large part come from parliamentary papers, official reports, departmental files, comment in newspapers and journals, minutes of meetings and conferences, memoranda, correspondence and from the recollections of some of those people involved who are still alive.

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Jurassic volcanic rocks in southeastern Arizona provide an opportunity to study the paleomagnetism of an autochthonous segment of the Mesozoic Cordilleran magmatic arc. The Corral Canyon sequence in the Patagonia Mountains is a 650 meter thick homoclinal sequence consisting of interbedded volcaniclastic red-beds, welded ash-flow tuff, and lavas. Rb/Sr isotopic analysis of eight whole rock tuff samples yields an isochron age of 171 ± 3 Ma. Welded tuffs in the Corral Canyon sequence possess a stable, primary magnetization carried in both magnetite and hematite that defines a paleomagnetic pole at 61.8°N, 116.0°E, alpha₉₅= 6.2°. This pole is considered to be a reliable Middle Jurassic reference pole for cratonic North America. Paleomagnetic study of the Canelo Hills volcanics welded tuff member also yields a stable, primary magnetization throughout a stratigraphic thickness of 600 meters. However, results from this formation are enigmatic and the mean pole is discordant with respect to Middle Jurassic reference poles. Various aspects of the paleomagnetic data indicate that discordance of the Canelo Hills volcanics pole is probably due to acquisition of remanent magnetization during a period of non-dipole behavior of the geomagnetic field. Dispersion of paleomagnetic directions suggests that the welded tuff member represents at most two cooling units and can be interpreted as a caldera-fill sequence. A revised Jurassic APW path differs significantly from available paths and has important implications for North American plate motion and paleolatitude. The spatio-temporal progression of reliable Jurassic paleopoles, in conjunction with Triassic and Early Cretaceous poles, is well described by paleomagnetic Euler pole analysis. The APW path is divided into three tracks, separated by two cusps. These cusps represent changes in the direction of North American absolute plate motion and can be correlated with global plate motion and intraplate deformation events at approximately 200-210 Ma and 150 Ma. Finally, the APW path presented herein predicts more southerly Late Triassic and Jurassic paleolatitudes for North America than have been suggested by previous authors. Using revised reference poles, there are no inclination anomalies within paleomagnetic data from Late Triassic and Early Jurassic rocks of Stikinia and Quesnellia (B.C., Canada).

A combination of geological and hydraulic techniques represents the most sensible approach to flood hazard analysis on alluvial fans. Hydraulic models efficiently yield predictions of flood depths and velocities, but the assumptions on which the models are based do not lead to accurate portrayals of natural fan processes. Geomorphological mapping, facies, mapping, and hydraulic reconstructions of past floods provide data on the location, types, and magnitude of flood hazards, respectively. Geological reconstructions of past floods should be compared with the results of hydraulic modeling before, potentially unsound, floodplain management decisions are implemented. The controversial Federal Emergency Management Agency procedure for delineating flood-hazard zones underestimated the extent, velocity, and depth of flow during recent floods on two alluvial fans by over 100, 25, and 70 percent, respectively. Flow on the alluvial fans occurs in one or more discontinuous ephemeral stream systems characterized by alternating sheetflood zones and channelized reaches. The importance of sheetflooding is greater on fans closer to the mountain front and with unstable channel banks. Channel diversions on five alluvial fans repeatedly occurred along low channel banks and bends where the greatest amount of overland flow is generated. Channel migration occurs through stream capture whereby overland flow from the main channel accelerates and directs erosion of adjacent secondary channels. The recurrence interval of major channel shifts is greater than 100 years, but minor changes occurred on all five fans during this century. Small aggrading flows are important, because they decrease bank heights and alter the location of greatest overland flow during subsequent floods. The results of this study demonstrate that (1) geological reconstructions of past floods can check the results of hydraulic models, (2) the character of flooding on alluvial fans can vary significantly in the same tectonic and climatic setting due to differences in drainage-basin characteristics, and (3) flood-hazard assessments on alluvial fans must be updated after each flood, because the location and timing of channel diversions can be affected by small floods.