ABSTRACT Rampart craters are omnipresent features on volatile-rich solid planetary surfaces. This raises the question whether, and how many, rampart craters are present on Earth. We reviewed the terrestrial impact crater record with regard to possible rampart morphologies and present detailed morphological analyses of these terrestrial craters here. Our results show that the Ries crater in Germany, Bosumtwi crater in Ghana, Tenoumer crater in Mauritania, Lonar crater in India, and Meteor crater in the United States are terrestrial rampart craters. The Ries and Bosumtwi craters can be classified as double-layer ejecta (DLE) craters, whereas Tenoumer, Lonar, and Meteor craters can be classified as single-layer ejecta (SLE) craters. Tenoumer and Meteor craters show rampart as well as common lunar-like ejecta characteristics within their ejecta blankets and, thus, appear to be hybrid craters. In addition, we discuss seven crater structures that show at least some morphological or lithological peculiarities that could provide evidence for possible ejecta ramparts. Considering the low number of terrestrial impact craters with well-preserved ejecta blankets, the relatively high proportion of rampart craters is astonishing. Obviously, the formation of layered or rampart craters is a common and not a rare process on Earth.

ABSTRACT Arizona has a wide variety of geological features relevant to planetary geology. The “Holey Tour” is a 2 d field trip (Phoenix-Flagstaff-Phoenix) that introduces participants to crater forms (hence the “holes” of the tour), including a maar, karst sinkhole, pit crater, cinder-cone craters, a volcano-tectonic depression, and the classic impact structure Meteor Crater. The Apollo astronaut field training site near Flagstaff is examined, which includes a terrain that was artificially generated to simulate a cratered lunar surface. In addition, planetary volcanism is discussed with stops that include a shield volcano, composite cone, silicic dome, and cinder cones; considerations include key variables in volcanic morphology, such as lava composition and rates of effusion. The general geology of Arizona is discussed throughout the trip and includes parts of the Colorado Plateau, the Basin and Range Province, and the Central Highlands (also called the “transition” zone). The trip can be adapted to meet the needs of any group, from secondary school students to established planetary scientists. This field trip generally follows the GSA guide published in GSA Special Paper 483 (available at https://pubs.geoscienceworld.org/gsa ): Greeley, R., 2011, The “Holey Tour” planetary geology field trip, Arizona, in Garry, W.B., and Bleacher, J.E., eds., Analogs for Planetary Exploration: Geological Society of America Special Paper 483, p. 377–391, https://doi.org/10.1130/2011.2483(23) .

Arizona has a wide variety of geological features relevant to planetary geology. The “Holey Tour” is a 2 d field trip (Phoenix-Flagstaff-Phoenix) that introduces participants to crater forms (hence the “holes” of the tour), including a maar, karst sinkhole, pit crater, cinder-cone craters, a volcano-tectonic depression, and the classic impact structure Meteor Crater. The Apollo astronaut field training site near Flagstaff is examined, which includes a terrain that was artificially generated to simulate a cratered lunar surface. In addition, planetary volcanism is discussed with stops that include a shield volcano, composite cone, silicic dome, and cinder cones; considerations include key variables in volcanic morphology, such as lava composition and rates of effusion. The general geology of Arizona is discussed throughout the trip and includes parts of the Colorado Plateau, the Basin and Range Province, and the Central Highlands (also called the “transition” zone). The trip can be adapted to meet the needs of any group, from secondary school students to established planetary scientists.

Catastrophic and unusual events on Earth such as bolide impacts, megafloods, supereruptions, flood volcanism, and subice volcanism may have devastating effects when they occur. Although these processes have unique characteristics and form distinctive features and deposits, we have difficulties identifying them and measuring the magnitude of their effects. Our difficulties with interpreting these processes and identifying their consequences are understandable considering their infrequency on Earth, combined with the low preservation potential of their deposits in the terrestrial rock record. Although we know these events do happen, they are infrequent enough that the deposits are poorly preserved on the geologically active face of the Earth, where erosion, volcanism, and tectonism constantly change the surface. Unlike the Earth, on Mars catastrophic and unusual features are well preserved because of the slow modification of the surface. Significant precipitation has not occurred on Mars for billions of years and there appears to be no discrete crustal plates to have undergone subduction and destruction. Therefore the ancient surface of Mars preserves geologic features and deposits that result from these extraordinary events. Also, unlike the other planets, Mars is the most similar to our own, having an atmosphere, surface ice, volcanism, and evidence of onceflowing water. So although our understanding of precursors, processes, and possible biological effects of catastrophic and unusual processes is limited on Earth, some of these mysteries may be better understood through investigating the surface of Mars.