Robert Craddock

Robert Craddock
Smithsonian Institution · Center for Earth and Planetary Studies (CEPS)

PhD

About

186
Publications
16,061
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Introduction
Bob Craddock conducts scientific research in the field of planetary geology with an emphasis on the origin and evolution of landforms on Mars, the Earth, and the Moon His analyses of impact crater modification support a warm, wet climate capable of sustaining rainfall and surface runoff. He has also proposed that Phobos and Deimos are the result of a giant impact. In addition, he conducts analog field investigations in central Australia and Hawaii.
Additional affiliations
June 1988 - present
Smithsonian Institution
Position
  • Geologist
June 1988 - present
Smithsonian Institution
Position
  • Geologist

Publications

Publications (186)
Article
Volcanic activity on Mars peaked during the Noachian and Hesperian periods but has continued since then in isolated locales. Elysium Planitia hosts numerous young, fissure-fed flood lavas with ages ranging from approximately 500 to 2.5 million years (Ma). We present evidence for a fine-grained unit that is atypical of aeolian deposits in the region...
Preprint
Full-text available
Volcanic activity on Mars peaked during the Noachian and Hesperian periods but has continued since then in isolated locales. Elysium Planitia hosts numerous young, fissure-fed flood lavas with ages ranging from approximately 500 to 2.5 million years (Ma). We present evidence for what may be the youngest volcanic deposit yet documented on Mars: a lo...
Article
Full-text available
The debate over the early Martian climate is among the most intriguing in planetary science. Although the geologic evidence generally supports a warmer and wetter climate, climate models have had difficulty simulating such a scenario, leading some to suggest that the observed fluvial geology (e.g. valley networks, modified landscapes) on the Martia...
Article
Full-text available
Estimates of river paleodischarges have been used to constrain the former climate of Mars. Paleodischarge has been calculated using mechanistic approximations of the channel bed‐shear stress at the threshold of particle motion or correlative width‐discharge relations derived from empirical terrestrial hydraulic geometry data. We apply both these me...
Preprint
Full-text available
The debate over the early Martian climate is among the most intriguing in planetary science. Although the geologic evidence generally supports a warmer and wetter climate, climate models have had difficulty simulating such a scenario, leading some to predict that the observed fluvial geology (e.g. valley networks, modified landscapes) on the Martia...
Conference Paper
Full-text available
Introduction: The early martian climate has been debated for decades and will continue to be a controversial topic for some time to come. The valley networks , which are fluvial features that are large enough to rival the largest erosional features on the Earth [1] (Figure 1), are the best evidence for an abundance of surface liquid water early in...
Article
A change in the global climate on early Mars is suspected from the geologic evidence of warmer wetter conditions that prevailed during the Noachian but stands in contrast to the dry and cold conditions observed currently. However, the timing and evolution of this climatic change represents a gap in our understanding of the history of Mars. Here, we...
Article
Full-text available
The climate of early Mars remains a topic of intense debate. Ancient terrains preserve landscapes consistent with stream channels, lake basins and possibly even oceans, and thus the presence of liquid water flowing on the Martian surface 4 billion years ago. However, despite the geological evidence, determining how long climatic conditions supporti...
Article
Full-text available
Impact craters on Mars have been extensively modified by ancient geologic processes that may have included rainfall and surface runoff, snow and ice, denudation by lava flows, burial by aeolian material, or others. Many of these processes can leave distinct signatures on the morphometry of the modified impact crater as well as the surrounding lands...
Article
Full-text available
One important, almost ubiquitous, tool for understanding the surfaces of solid bodies throughout the solar system is the study of impact craters. While measuring a distribution of crater diameters and locations is an important tool for a wide variety of studies, so too is measuring a crater's “depth.” Depth can inform numerous studies including the...
Conference Paper
Full-text available
Introduction: The climate of early Mars has been a topic of intense debate for decades. Although most investigators believe that the geology, including the valley networks (Figure 1), indicates the presence of surface water, disagreement has persisted regarding how warm the surface must have been and how long such conditions may have existed. Clima...
Article
Full-text available
Several explanations have been proposed for the temporal differences in geologic processes associated with the modification of martian impact craters, which occurred throughout the Noachian, and the formation of valley networks, which occurred during the Noachian/Hesperian transition. Here we show that it could be a result of the changing nature of...
Article
Full-text available
We analyzed the morphometry of basaltic rock populations that have been emplaced or affected by a variety of geologic processes, including explosive volcanic eruptions (as a proxy for impact cratering), catastrophic flooding, frost shattering, salt weathering, alluvial deposition, and chemical weathering. Morphometric indices for these rock populat...
Article
Full-text available
Linear dunes are the most common dune form found on planetary surfaces, yet questions remain about their formation. Temporal observations of a linear dune located in the Simpson Desert of central Australia were made to monitor dune movement and to test competing hypotheses regarding linear dune formation. Our observations were collected on three se...
Conference Paper
Full-text available
Many Geologic features attest to the fact that liquid water was once stable on the Martian surface. The erosional processes necessary to create these features must have been supported by a climate that is much different than today. However, the evolution of these primitives conditions toward the current dry and cold Martian climate where the erosio...
Article
We present preliminary analyses of basaltic lithic fragments found in volcanic tephra, eolian dunes, fluvial deposits, and glacial moraines found in Hawaii.
Article
Understanding planetary landforms, including the theater-headed valleys (box canyons) of Mars, usually depends on interpreting geological processes from remote-sensing data without ground-based corroboration. Here we investigate the origin and development of two Mars-analog theater-headed valleys in the hyperarid Atacama Desert of northern Chile. P...
Article
The influx of new data received from recent spacecraft missions, the study of Martian meteorites, recent progress in early climate modeling, the growing evidence for abundant water on early Mars, and the rapid pace of new discoveries about the origin and diversity of life on Earth have reinvigorated interest in both the conditions that prevailed on...
Article
The precise timing of valley network drainage basin formation is critical to understanding the history of water and climate on Mars. To determine whether there are any variations in ages within separate drainage basins and subbasins that may reflect local or regional variations in climate or resetting from resurfacing (e.g., impact ejecta or lava f...
Article
Here we review our current understanding of fluvial features on Mars and their implications for the history of water and climate.
Conference Paper
Full-text available
Dark aeolian bedforms on Mars are thought to consist of volcanic materials due to their mineral assemblages, which are common to basalts. However, the sediment source is still debated and needs further affirmation. Basaltic dunes on Earth are rare and can only be found in a few places including New Zealand, Iceland, the western USA, Peru, and Hawai...
Article
Full-text available
A number of studies have attempted to characterize Martian valley and channel networks. To date, however, little attention has been paid to the role of lithology, which could influence the rate of incision, morphology, and hydrology as well as the characteristics of transported materials. Here, we present an analysis of the physical and hydrologic...
Article
Noachian mars was dry but eroded. Mars at the Noachian-Hesperian was wetter. Mars during the Hesperian to Amazonian supported limited fluvial incision.
Article
The hydro-climatic evolution of Mars can be subdivided into four epochs with distinct environments: Earliest Mars, the Noachian, the Noachian-Hesperian boundary, and later events. Many uncertainties remain about their enviroments and history.
Article
We document the physical and geochemical changes that take place as basaltic materials are transported by a variety of geologic processes, including wind, water, and ice. We will present results from quantitative, microscopic, and SEM analyses.
Article
Dark aeolian deposits on Mars are thought to consist of volcanic materi­als due to their mineral assemblages, which are common to basalts. However, the sediment source is still debated. Basaltic dunes on Earth are promising analogues for providing further insights into the assumed basaltic sand dunes on Mars. In our study we characterize basaltic d...
Article
Full-text available
Aeolian dune fields have been described on Earth, Mars, Venus, and Titan. The amount and fidelity of data being returned from orbiting spacecraft and landers have enabled a new era in aeolian studies. This progress report presents an overview of the latest planetary geomorphic studies characterizing aeolian processes on extraterrestrial surfaces. O...
Conference Paper
Full-text available
Dark aeolian deposits on Mars are thought to consist of volcanic materials due to their mineral assemblages, which are common to basalts. However, the sediment source is still debated. Basaltic dunes on Earth are promising analogues for providing further insights into the assumed basaltic sand dunes on Mars. The basaltic dunes in Hawaii are especia...
Conference Paper
Full-text available
Our study is intended to (i) characterize the basaltic sands petrologically, (ii) to determine if the dune sands originate from the stripping of Keanakako'i tephra or from local reworked tephra emplaced by larger phreatomagmatic eruptions, (iii) to determine the material's transport mechanisms (i.e., fluvial and/or aeolian), and (iv) to assess the...
Article
Full-text available
Despite many efforts an adequate theory describing the origin of Phobos and Deimos has not been realized. In recent years a number of separate observations suggest the possibility that the Martian satellites may have been the result of giant impact [1]. Similar to the Earth-Moon system, Mars has too much angular momentum. A planetesimal with 0.02 M...
Article
Valley networks are often cited as the best evidence that liquid water was stable on the surface of Mars early in its history [1]. However, geologic evidence is beginning to emerge indicating that the period of time valley networks were forming was actually short-lived and restricted primarily to the end of the Noachian/beginning of the Hesperian [...
Article
Martian gullies are often morphologically similar to terrestrial gullies and also appear young. The current environment on Mars does not support liquid water. Several processes may have been involved in their formation. At least some gullies were formed by dry mass wasting.
Article
Some morphometric differences between terrestrial and Martian valley networks may reflect the precursor topography on Mars, particularly impact basins or tectonic slopes. To evaluate these possible influences, we mapped highland watersheds in nine study areas that sample a range of geographic and topographic settings. We collected data including la...
Article
Full-text available
Despite many efforts an adequate theory describing the origin of Phobos and Deimos has not been realized. In recent years a number of separate observations suggest the possibility that the martian satellites may have been the result of giant impact. Similar to the Earth-Moon system, Mars has too much angular momentum. A planetesimal with 0.02 Mars...
Conference Paper
Our objectives are to (1) determine the history of basaltic dunes located in the Ka'u Desert of Hawaii, (2) ascertain changes in the characteristics of basaltic sediments as they are transported, and (3) acquire the VNIR spectra of these materials.
Article
Hoke et al. (2004, Geology 32, 605-608) published one of the more prominent studies suggesting a groundwater-sapping origin for theater-headed valleys (box canyons), focusing on sites in the hyperarid Atacama Desert of northern Chile. Their study was based on remote-sensing datasets, digital topography, geologic maps, and regional hydrology rather...
Conference Paper
Dark dunes are the dominant aeolian bedforms on Mars and consist of ancient volcanic ashes and reworked basaltic lavas. Basaltic dunes are rare on Earth and only occur in limited areas, such Hawaii. Because the Hawaiian dunes are composed of reworked basaltic sediments transported by eolian processes, they are a promising subject matter of analogy...
Conference Paper
Full-text available
Samples of tephra collected in Hawaii’s Ka’u Desert are investigated by means of different laboratory methods in order to examine their detailed mineral assemblages and chemistries. The analyses involve spectral, microscopic, and microporobe investigations. Spectral analyses reveal similar mineral assemblages as Martian dark dunes pointing to a sim...
Conference Paper
Full-text available
Dark basaltic dunes represent the majority of Martian eolian bedforms. However, on Earth there are only few places where basaltic dunes can be found. Is has been suggested that the Marian dunes sands are volcanic in origin because their mineralogical composition consists of pyroxene and olivine. The dark dunes in Ka'u Desert on the Big Island of Ha...
Article
Martian valley networks provide the best evidence that the climate on Mars was different in the past. Although these features are located primarily in heavily cratered terrain of Noachian age (>3.7 Ga), the ages of the features and the time when they were active is not well understood. From superposed craters several recent global studies determine...
Conference Paper
Here we report the general physical and chemical characteristics of basaltic dunes located in the Ka'u Desert of Hawaii.
Article
Topographic controls on martian valley networks are mostly large, early Noachian features that underwent slow aqueous weathering and erosion in an arid to hyperarid Noachian paleoclimate, followed by valley entrenchment around the Noachian/Hesperian transition.
Article
This study will establish an analogous eruptive and emplacement history of the range of shield volcanos and volcanic provinces found both on Syria Planum, Mars, and on the Galapagos and Kilauea, Hawaii, volcanos on Earth.
Conference Paper
Full-text available
In this work we compare spectra of sand samples of terrestrial dark dunes derived in Ka'u Desert (Hawaii) with that of dark martian dunes. We find indications for a similar origin of the dark sands.
Article
Full-text available
Buried river channels and valleys have proven to be valuable economic and agricultural resources. Often they are ecologically important refugia and in some instances, such as in the Sahara Desert, serve as dramatic reminders of the climatic changes that have taken place. Here we report the determination of a fluvial landscape that is substantially...
Article
Volcanism has been a major process during most of the geologic history of Mars. Based on data collected from terrestrial basaltic eruptions, we assume that the volatile content of martian lavas was typically ∼0.5 wt.% water, ∼0.7 wt.% carbon dioxide, ∼0.14 wt.% sulfur dioxide, and contained several other important volatile constituents. From the ge...
Article
Terrestrial volcanoes studies are being used to develop techniques for interpretation of the styles of volcanic processes and the evolution of volcanic systems on Mars. Detailed characterizations of terrestrial flow fields provide critical evaluation of flow field emplacement on planetary surfaces, namely at vent fissure type features associated to...
Article
Full-text available
A line-heat source apparatus was used to measure thermal conductivities of a lightly cemented fluvial sediment (salinity = 1.1 g · kg-1), and the same sample with the cement bonds almost completely disrupted, under low pressure, carbon dioxide atmospheres. The thermal conductivities of the cemented sample were approximately 3× higher, over the rang...
Article
We are conducting field studies in Hawaii and in Iceland to understand the formation of parasitic shield volcanoes and their related lava flows. The rheological properties of Mars Syria Planum small shields volcanoes make them a good analog.
Article
The exact timing of valleys networks is still not well understood. We set out to test the reliability of different counting methods applied to Parana Valles using a large dataset of HR images that allow to reduce uncertainties in age determination.
Chapter
IntroductionEarly observationsDistribution, age, origin and morphology of valley networksMorphometryAlluvial depositsHydrologySummaryAcknowledgementsReferences
Article
We analyze modified impact craters in the Aeolis highlands to determine the types and intensity of geologic processes that have occurred through time on Mars. Our results indicate long-lived and intense surface runoff in this area.
Preprint
Full-text available
The gullies on Mars were discovered in the year 1999. Their aspect suggests that they had been formed recently on Martian slopes. Since then several hypotheses have appeared trying to explain the presence of these gullies. The main hypotheses are the ones which suggest that some liquid, water or CO2, was responsible for modeling the gullies and one...
Poster
Since their discovery many different theories have been put forward to explain the origin of Martian gullies. Each theory has certain weaknesses, however, and the formation of these features remains poorly understood. Distinctive morphologic variations exist that have often been ignored. Here we present experimental results that attempt to create M...
Article
It's clear from geologic features such as the Tharsis volcanoes, analyses of the SNC meteorites, multispectral data from orbiting spacecraft, and in situ measurements made by landers that the martian surface is composed primarily of basalt. Spacecraft data also suggest that this basaltic surface has been broken down into friable materials produced...
Article
A fluvial sample with a salt content of 1.1 g/kg has a thermal conductivity approximately 3× greater than that of the same sample with the cement bonds broken. Due to the cement bonds that were broken during collection and transport, this effect represent
Article
It is estimated that linear dunes represent 40 percent of all dunes on Earth. Linear dunes have also been found on every terrestrial planet with an appreciable atmosphere, including Mars, Venus and Titan. Remarkably, however, despite how prevalent they are very little is known about their formation, chronology and their interaction with adjacent se...
Article
Full-text available
A line-heat source apparatus was used to measure thermal conductivities of natural fluvial and eolian particulate sediments under low pressures of a carbon dioxide atmosphere. These measurements were compared to a previous compilation of the dependence of thermal conductivity on particle size to determine a thermal conductivity-derived particle siz...
Article
The results of thermal conductivity measurements of natural fluvial and eolian samples are presented. The larger particle sizes appear to control the thermal conductivity.
Article
At theater-headed valleys in Utah and Arizona, we found diversity relative to the Laity-Malin sapping model, large discharges of ephemeral contributing streams from the plateau surface, and substantial erosion of vegetated alluvial fill since 1985.
Article
Full-text available
In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity...
Article
Full-text available
Received 15 April 2005; revised 16 September 2005; accepted 21 September 2005; published 2 December 2005. (1) To explain the much higher denudation rates and valley network development on early Mars (>� 3.6 Gyr ago), most investigators have invoked either steady state warm/wet (Earthlike) or cold/dry (modern Mars) end-member paleoclimates. Here we...