Change in the magnetic properties of bituminous coal intruded by an igneous dike, Dutch Creek Mine, Pitkin County, Colorado

Magnetization measurements have been made on natural coke–coal samples collected at various distances from a felsic porphyry dike in a coal seam in Dutch Creek Mine, Colorado to help characterize the nature and distribution of the iron-bearing phases. The magnetization passes through a maximum at the coke-to-coal transition about 31 cm from the dike contact. The magnetic measurements support the geochemical data indicating that magmatic fluids along with a high-temperature gas pulse moved into the coal bed. Interaction of the magmatic fluids with the coal diminished the reducing power of the thermal gas pulse from the dike to a point about 24 cm into the coal. The hot reducing gas penetrated further and produced a high temperature (400–525°C) zone (at about 31 cm) just ahead of the magmatic fluids. Metallic iron found in this zone is the principal cause of the observed high magnetization. Beyond this zone, the temperature was too low to alter the coal significantly.     

STABILITY OF NIANCHU RIVER AFTER REGULATION BY STRAIGHTENING: A CASE STUDY FROM TIBET, CHINA

IINTRODUCTIONTheNianchuRiverCatchmentisoneofthemaingrainproducingareasofTibet.TheengineeringregulationoftheriverisanimportantcomponentofstatekeyprojectofChina,"OneRiverandTwoTributariesProject"."OneRiver"herestandsfortheYarlungZhangboRiverandthe"TwoTributaries"aretheNianchuRiverandtheLasaRiverinCentral-SouthernTibet.InordertoimprovethewaterresourcesandtopreventfloodinginTibet,aseriesofhydropowerstations,irrigationdiversionprojects,floodcontrollevees,andreforestationprogramshaveb…     

Use of incipient motion data for backward erosion piping models

Backward erosion piping involves the gradual removal of granular material under the action of water flow from the foundation of a dam or levee, whereby shallow pipes are formed that grow in the direction opposite to the flow. This pipe-forming process can ultimately lead to failure of a water-retaining structure and is considered one of the most important failure mechanisms for dikes and levees in the Netherlands and the United States. Modeling of this mechanism requires the assessment of hydraulic conditions in the pipe, which are controlled by the particle equilibrium at the pipe wall. Since the pipe's dimensions are controlled by the inflow to the pipe from the porous medium, the flow through the pipe is thought to be laminar for fine- to medium-grained sands. The literature provides data for incipient motion in laminar flow, which is reviewed here and complemented with data from backward erosion experiments. The experiments illustrate the applicability of the laminar incipient motion data to determine the erosion pipe dimensions and corresponding pipe hydraulics for fine- to medium-grained sands, for the purpose of backward erosion piping modeling.     

Sources of debris flow material in burned areas

The vulnerability of recently burned areas to debris flows has been well established. Likewise, it has been shown that many, if not most, post-fire debris flows are initiated by runoff and erosion and grow in size through erosion and scour by the moving debris flow, as opposed to landslide-initiated flows with little growth. To better understand the development and character of these flows, a study has been completed encompassing 46 debris flows in California, Utah, and Colorado, in nine different recently burned areas. For each debris flow, progressive debris production was measured at intervals along the length of the channel, and from these measurements graphs were developed showing cumulative volume of debris as a function of channel length. All 46 debris flows showed significant bulking by scour and erosion, with average yield rates for each channel ranging from 0.3 to 9.9 m³ of debris produced for every meter of channel length, with an overall average value of 2.5 m³/m. Significant increases in yield rate partway down the channel were identified in 87% of the channels, with an average of a three-fold increase in yield rate. Yield rates for short reaches of channels (up to several hundred meters) ranged as high as 22.3 m³/m. Debris was contributed from side channels into the main channels for 54% of the flows, with an average of 23% of the total debris coming from those side channels. Rill erosion was identified for 30% of the flows, with rills contributing between 0.1 and 10.5% of the total debris, with an average of 3%. Debris was deposited as levees in 87% of the flows, with most of the deposition occurring in the lower part of the basin. A median value of 10% of the total debris flow was deposited as levees for these cases, with a range from near zero to nearly 100%. These results show that channel erosion and scour are the dominant sources of debris in burned areas, with yield rates increasing significantly partway down the channel. Side channels are much more important sources of debris than rills. Levees are very common, but the size and effect on the amount of debris that reaches a canyon mouth is highly variable.     

Erosional equivalences of levees: Steady and intermittent wave overtopping

Present criteria for acceptable grass covered levee overtopping are based on average overtopping values but do not include the effect of overtopping duration. This paper applies experimental steady state results for acceptable overtopping to the case of intermittent wave overtopping. Laboratory results consisting of velocities and durations for acceptable land side levee erosion due to steady flows are examined to determine the physical basis for the erosion. Three bases are examined: (1) velocity above a threshold value, (2) shear stress above a threshold value, and (3) work above a threshold value. The work basis provides the best agreement with the data and a threshold work value and a work index representing the summation of the product of work above the threshold and time are developed. The governing equations for flow down the land side of a levee establish that the flows near the land side levee toe will be supercritical. Wave runup is considered to be Rayleigh distributed with the runup above the levee crest serving as a surrogate for overtopping. Two examples illustrating application of the methodology are presented. Example 1 considers three qualities of grass cover: good, average, and poor. The required levee elevations for these three covers differ by 1.8 m. The results for Example 1 are compared with the empirical criteria of 0.1 liters per second per meter (l/s per m), 1.0  l/s per m, and 10.0  l/s per m. It is found that the required crest elevation by the methodology recommended herein for the “poor” cover is only slightly lower than for the criterion for average overtopping of q=10.0  l/s per m but significantly lower than for the overtopping criterion of 1.0 and 0.1 m/s per m. Example 2 considers two durations of the peak surge with the result that the longer duration peak surge requires a levee that is higher by approximately 0.8 m.     

Construction dynamics of a lava channel

We use a kinematic GPS and laser range finder survey of a 200 m-long section of the Muliwai a Pele lava channel (Mauna Ulu, Kilauea) to examine the construction processes and flow dynamics responsible for the channel–levee structure. The levees comprise three packages. The basal package comprises an 80–150 m wide ′a′a flow in which a ∼2 m deep and ∼11 m wide channel became centred. This is capped by a second package of thin (<45 cm thick) sheets of pahoehoe extending no more than 50 m from the channel. The upper-most package comprises localised ′a′a overflows. The channel itself contains two blockages located 130 m apart and composed of levee chunks veneered with overflow lava. The channel was emplaced over 50 h, spanning 30 May–2 June, 1974, with the flow front arriving at our section (4.4 km from the vent) 8 h after the eruption began. The basal ′a′a flow thickness yields effusion rates of 35 m³ s⁻¹ for the opening phase, with the initial flow advancing across the mapped section at ∼10 m/min. Short-lived overflows of fluid pahoehoe then built the levee cap, increasing the apparent channel depth to 4.8 m. There were at least six pulses at 90–420 m³ s⁻¹, causing overflow of limited extent lasting no more than 5 min. Brim-full flow conditions were thus extremely short-lived. During a dominant period of below-bank flow, flow depth was ∼2 m with an effusion rate of ∼35 m³ s⁻¹, consistent with the mean output rate (obtained from the total flow bulk volume) of 23–54 m³ s⁻¹. During pulses, levee chunks were plucked and floated down channel to form blockages. In a final low effusion rate phase, lava ponded behind the lower blockage to form a syn-channel pond that fed ′a′a overflow. After the end of the eruption the roofed-over pond continued to drain through the lower blockage, causing the roof to founder. Drainage emplaced inflated flows on the channel floor below the lower blockage for a further ∼10 h. The complex processes involved in levee–channel construction of this short-lived case show that care must be taken when using channel dimensions to infer flow dynamics. In our case, the full channel depth is not exposed. Instead the channel floor morphology reflects late stage pond filling and drainage rather than true channel-contained flow. Components of the compound levee relate to different flow regimes operating at different times during the eruption and associated with different effusion rates, flow dynamics and time scales. For example, although high effusion rate, brim-full flow was maintained for a small fraction of the channel lifetime, it emplaced a pile of pahoehoe overflow units that account for 60% of the total levee height. We show how time-varying volume flux is an important parameter in controlling channel construction dynamics. Because the complex history of lava delivery to a channel system is recorded by the final channel morphology, time-varying flow dynamics can be determined from the channel morphology. Developing methods for quantifying detailed flux histories for effusive events from the evidence in outcrop is therefore highly valuable. We here achieve this by using high-resolution spatial data for a channel system at Kilauea. This study not only indicates those physical and dynamic characteristics that are typical for basaltic lava flows on Hawaiian volcanoes, but also a methodology that can be widely applied to effusive basaltic eruptions.