Abstract One of the geohazards associated with coal mining is subsidence. Coal was originally extracted where it outcropped, then mining became progressively deeper via shallow workings including bell pits, which later developed into room-and-pillar workings. By the middle of the 1900s, coal was mined in larger open pits and underground by longwall mining methods. The mining of coal can often result in the subsidence of the ground surface. Generally, there are two main types of subsidence associated with coal mining. The first is the generation of crown holes caused by the collapse of mine entries and mine roadway intersections and the consolidation of shallow voids. The second is where longwall mining encourages the roof to fail to relieve the strains on the working face and this generates a subsidence trough. The ground movement migrates upwards and outwards from the seam being mined and ultimately causes the subsidence and deformation of the ground surface. Methods are available to predict mining subsidence so that existing or proposed structures and land developments may be safeguarded. Ground investigative methods and geotechnical engineering options are also available for sites that have been or may be adversely affected by coal mining subsidence.

Abstract Old chalk and flint mine workings occur widely across southern and eastern England. Over 3500 mines are recorded in the national Stantec Mining Cavities Database and more are being discovered each year. The oldest flint mines date from the Neolithic period and oldest chalk mines from at least medieval times, possibly Roman times. The most intensive period for mining was during the 1800s, although some mining activities continued into the 1900s. The size, shape and extent of the mines vary considerably with some types only being found in particular areas. They range from crudely excavated bellpits to more extensive pillar-and-stall styles of mining. The mines were created for a series of industrial, building and agricultural purposes. Mining locations were not formally recorded so most are discovered following the collapse of the ground over poorly backfilled shafts and adits. The subsidence activity, often triggered by heavy rainfall or leaking water services, poses a hazard to the built environment and people. Purpose-designed ground investigations are needed to map out the mine workings and carry out follow-on ground stabilization after subsidence events. Where mine workings can be safely entered they can sometimes be stabilized by reinforcement rather than infilling.

Central pit craters are common on ice-rich bodies, such as Mars, Ganymede, and Callisto. Mars and Ganymede represent the two end members regarding target characteristics (mixed ice and soil for Mars vs. almost pure ice for Ganymede). Comparisons of central pit craters on these two bodies can provide insights into the environmental conditions under which these craters form and provide constraints on the proposed formation models. This analysis includes 1604 central pit craters on Mars and 471 central pit craters on Ganymede. Martian central pit craters are divided into floor pits and summit pits, whereas all central pit craters on Ganymede are floor pits. Central pit craters form in similar-diameter ranges on both Mars and Ganymede when gravity differences are considered, and both bodies show no regional variations in pit crater distribution within the ±60° latitude zone. Martian floor pits are larger relative to their parent crater than summit pits, but the Ganymede pit/crater diameter ratio is larger than for either central pit type on Mars. Central pits have formed over the entire history of both bodies, and there is no indication that excavation depths have varied over time. Lack of crater floor updoming in Martian floor pit craters indicates that low concentrations of ice (estimated at ~20%) still allow production of central pits. The results of this study argue against central peak collapse as the formation mechanism for central pit craters. Excavation into a subsurface liquid layer cannot be ruled out but is difficult to support based on the distributions and consistencies in excavation depth on both bodies. These results support the model of vaporization and gas escape for central pit formation on both Mars and Ganymede.

We compared the target types and the morphologies and morphometries of various features within fresh complex craters on Mars to assess target dependence. The wide scatter in depth-diameter data from Martian craters is more pronounced than for lunar or Mercurian craters. This was previously assumed to be predominantly due to significant degrees of denudation and secondary infilling of the Martian craters. However, our data for fresh craters still exhibit a wide variation, which we interpret to be the result of comparatively higher target heterogeneity on Mars. Complex central peaks exhibit some crater diameter dependence, preferentially occurring in craters >50 km. Neither peak complexity nor geometry shows any statistical correlation with target type. Although central peak heights and aspect ratios do not exhibit any clear target dependence, they do appear to be correlated—higher peaks possess narrower aspect ratios. Floor and summit pits appear to be more common on lava targets than sedimentary targets, contrary to earlier studies with smaller sample sizes. This observation imposes additional constraints on models proposed for the origin of pits, especially those models that require the presence of volatiles in the target. The ability to correlate target type with crater morphologies/morphometries is highly contingent upon both the surface geology and the actual geology at depth. Some weak correlations may reflect our current limited understanding of the sub-surface geology of Mars. Information on the deeper lithologies acquired through future missions may help resolve the true effect of subsurface competence on intracrater structure.