An examination of some uncertainties associated with estimates of sedimentation rates and tectonic subsidence

Abstract The sensitivity of backstripping calculations (sedimentation rates and tectonic subsidence) to uncertainties regarding porosity reduction is examined. Models simulating compaction and externally sourced cementation are considered to provide first-order bounds on the thickness and mass changes for individual sedimentary units. These bounds can be used to estimate uncertainties in sedimentation rate and subsidence estimates. With these models, the timing of cement development can be regarded as unimportant for backstripping calculations. Calculations have been made to evaluate the effect on backstripping calculations of uncertainties in sediment porosity, density and the mechanisms of porosity reduction. Departures from theoretically predicted subsidence curves of the order of 100 m or so have been variously interpreted as the result of fluctuations or uncertainties in sea-level, palaeobathymetry, tectonic stress, sedimentation rates and stratigraphic age. Two examples are given to illustrate that such departures may occur in some subsidence curves merely as a result of imprecise assumptions regarding porosity reduction. Consideration should be given to the uncertainties in models for porosity reduction when using subsidence curves to infer second order tectonic influence during basin evolution.     

High-frequency oscillations in a solar active region coronal loop

The Solar Eclipse Corona Imaging System (SECIS) was used to record high-cadence observations of the solar corona during the total solar eclipse of 1999 August 11. During the 2 min 23.5 s of totality, 6364 images were recorded simultaneously in each of the two channels: a white light channel, and the Fe  xiv (5303 Å) 'green line' channel ( T ∼2 MK) . Here we report initial results from the SECIS experiment, including the discovery of a 6-s intensity oscillation in an active region coronal loop.     

Active-Region Monitoring and Flare Forecasting – I. Data Processing and First Results

This paper discusses a near real-time approach to solar active-region monitoring and flare prediction using the Big Bear Solar Observatory Active Region Monitor (ARM). Every hour, ARM reads, calibrates, and analyses a variety of data including: full-disk Hα images from the Global Hα Network; EUV, continuum, and magnetogram data from the Solar and Heliospheric Observatory (SOHO); and full-disk magnetograms from the Global Oscillation Network Group (GONG). For the first time, magnetic gradient maps derived from GONG longitudinal magnetograms are now available on-line and are found to be a useful diagnostic of flare activity. ARM also includes a variety of active-region properties from the National Oceanic and Atmospheric Administration's Space Environment Center, such as up-to-date active-region positions, GOES 5-min X-ray data, and flare-to-region identifications. Furthermore, we have developed a Flare Prediction System which estimates the probability for each region to produce C-, M-, or X-class flares based on nearly eight years of NOAA data from cycle 22. This, in addition to BBSO's daily solar activity reports, has proven a useful resource for activity forecasting. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1020950221179     

Mantle hotspots, plumes and regional tectonics as causes of intraplate magmatism

In continental areas it is often difficult to determine the cause of intraplate magmatism. Large volumes of magma, high eruption rates, and the presence of a hotspot trace on the adjacent ocean floor, are all evidence for the presence of an anomalously hot mantle. However, in many continental magmas there are chemical variations with time which are inferred to reflect changes from asthenospheric to predominantly lithospheric source regions, or vice versa. It is argued that these chemical characteristics constrain whether magmatism was triggered by the emplacement of a mantle plume, or by lithospheric extension.     

Scientists' warning on extreme wildfire risks to water supply

2020 is the year of wildfire records. California experienced its three largest fires early in its fire season. The Pantanal, the largest wetland on the planet, burned over 20% of its surface. More than 18 million hectares of forest and bushland burned during the 2019–2020 fire season in Australia, killing 33 people, destroying nearly 2500 homes, and endangering many endemic species. The direct cost of damages is being counted in dozens of billion dollars, but the indirect costs on water-related ecosystem services and benefits could be equally expensive, with impacts lasting for decades. In Australia, the extreme precipitation (“200 mm day −1 in several location”) that interrupted the catastrophic wildfire season triggered a series of watershed effects from headwaters to areas downstream. The increased runoff and erosion from burned areas disrupted water supplies in several locations. These post-fire watershed hazards via source water contamination, flash floods, and mudslides can represent substantial, systemic long-term risks to drinking water production, aquatic life, and socio-economic activity. Scenarios similar to the recent event in Australia are now predicted to unfold in the Western USA. This is a new reality that societies will have to live with as uncharted fire activity, water crises, and widespread human footprint collide all-around of the world. Therefore, we advocate for a more proactive approach to wildfire-watershed risk governance in an effort to advance and protect water security. We also argue that there is no easy solution to reducing this risk and that investments in both green (i.e., natural) and grey (i.e., built) infrastructure will be necessary. Further, we propose strategies to combine modern data analytics with existing tools for use by water and land managers worldwide to leverage several decades worth of data and knowledge on post-fire hydrology.     

Sorted clastic stripes, lobes and associated gullies in high-latitude craters on Mars: Landforms indicative of very recent, polycyclic ground-ice thaw and liquid flows

Self-organised patterns of stone stripes, polygons, circles and clastic solifluction lobes form by the sorting of clasts from fine-grained sediments in freeze-thaw cycles. We present new High Resolution Imaging Science Experiment (HiRISE) images of Mars which demonstrate that the slopes of high-latitude craters, including Heimdal crater - just 25 km east of the Phoenix Landing Site - are patterned by all of these landforms. The order of magnitude improvement in imaging data resolution afforded by HiRISE over previous datasets allows not only the reliable identification of these periglacial landforms but also shows that high-latitude fluviatile gullies both pre- and post-date periglacial patterned ground in several high-latitude settings on Mars. Because thaw is inherent to the sorting processes that create these periglacial landforms, and from the association of this landform assemblage with fluviatile gullies, we infer the action of liquid water in a fluvio-periglacial context. We conclude that these observations are evidence of the protracted, widespread action of thaw liquids on and within the martian regolith. Moreover, the size frequency statistics of superposed impact craters demonstrate that this freeze-thaw environment is, at least in Heimdal crater, less than a few million years old. Although the current martian climate does not favour prolonged thaw of water ice, observations of possible liquid droplets on the strut of the Phoenix Lander may imply significant freezing point depression of liquids sourced in the regolith, probably driven by the presence of perchlorates in the soil. Because perchlorates have eutectic temperatures below 240 K and can remain liquid at temperatures far below the freezing point of water we speculate that freeze-thaw involving perchlorate brines provides an alternative “low-temperature” hypothesis to the freeze-thaw of more pure water ice and might drive significant geomorphological work in some areas of Mars. Considering the proximity of Heimdal crater to the Phoenix Landing Site, the presence of such hydrated minerals might therefore explain the landforms described here. If this is the case then the geographical distribution of martian freeze-thaw landforms might reflect relatively high temperatures (but still below 273 K) and the locally elevated concentration of salts in the regolith.