Global Tectonic and Volcanic Activity of the Last One Million Years

Paul D. Lowman Jr.

Code 921, NASA/Goddard Space Flight Center, Greenbelt, MD 20771

April 1997

Also see "Digital Tectonic Activity Map"

Map of Global Tectonic and Volcanic Activity of the Last One Million Years
Larger version (284k)

To obtain a copy of this map please contact the author.

Seismic Epicenters Seismic Epicenters (39k) or (129k)

Polar Seismicity Polar Seismicity (30k) or (100k)

Polar Tectonics Polar Tectonics (35k) or (189k)

This map is not copyrighted and may be freely reproduced if the source is credited.

GLOBAL TECTONIC AND VOLCANIC ACTIVITY OF THE
LAST ONE MILLION YEARS

Paul D. Lowman Jr.
NASA/Goddard Space Flight Center (Code 921)
Greenbelt, Maryland 20771


 April 1997

The maps on these sheets are intended to give a schematic and generalized but realistic view of the Earth's major tectonic and volcanic features active within the last one million years. Originally presented at the 1980 International Geological Congress, the main (equator-centered) map has been up-dated to take advantage of recent advances such as the 1994 compilation of world volcanoes by Simkin and Siebert. It is presented here, with the original polar projection maps, because of its relevance to global change and geologic hazard studies.

The well-known geologic maxim, "the present is the key to the past," has a complement: the present is the key to the future, both with caveats that need not be discussed here. The key word in both is "present." The Earth is 4.5 billion years old, and the geologic events of a single year, decade, or even century are not representative of the "present" in terms of geologic time. The historical record of volcanic activity, for example, goes back only a few thousand years, yet there are innumerable apparently extinct volcanoes still potentially active. However, conventional geologic maps do not give a good view of the geologic present either, being cumulative representations of features formed over hundreds of millions or even billions of years. There is thus a gap between geologic maps and maps showing historically recorded volcanism and tectonism. Those presented here are intended to bridge this gap by showing volcanic and tectonic features active within the last one million years.

The one million year period was chosen primarily because features such as volcanoes, lava flows, and fault scarps survive as grossly recognizable landforms for about a million years in most land areas. Orbital photography and Landsat imagery have been used, directly and indirectly, in compilation of this map. In some areas, notably south-central Asia, our first realistic knowledge of regional tectonism came from Landsat imagery as used by Molnar and Tapponnier in their 1975 study. Many unmapped individual volcanoes and even volcanic fields have been discovered on orbital photography, and little known ones brought to the compiler's attention. It is believed that the map thus gives a much more comprehensive picture of continental volcanism than previously available (Christy and Lowman, 1995). However, marine investigations continue to uncover areas of previously unknown active subsea volcanism and further additions to this map will no doubt be made in future editions.

A new feature of the present edition is approximate representation of the Earth's continental/oceanic crustal dichotomy. Continental margins are much more fundamental features than coastlines, and the present map shows such margins primarily as the edge of the continental shelves (the continental slopes), with the proviso that the slopes may not be a sharp boundary between continental and oceanic crust. Furthermore, there are numerous features of the ocean basins underlain by continental crust. For example, the Lord Howe Rise northwest of New Zealand is largely at abyssal depths, over 1500 meters, but is known to consist of continental (sialic) crust. The Rockall Plateau in the North Atlantic similarly consists of granitic rocks. On the other hand, some prominent marine features, such as the Kerguelen Plateau, are apparently oceanic in composition, and are not shown on the map. The distribution of the "mainly oceanic crust" is accordingly based on a combination of bathymetric, geological, and geophysical data. Two references of particular value in drawing this aspect of the map are the compilation edited by Burk and Drake (1974) and the paper by Nur and Ben-Avraham (1982) in a special JGR issue on accretion tectonics.

An important aspect of these maps is their representation of continental tectonism, in particular the broad diffuse nature of supposed plate boundaries. The greater deformability of continental crust has been recognized for many years. Its cartographic importance is the near impossibility of representing plate boundaries in continents simply, as done by many "plate maps." The maps presented here are offered as views of continental tectonism more realistic than mathematical plate models.

Plate motion and rigidity have been directly measured in many areas by space geodesy, specifically satellite laser ranging and very long baseline interferometry, and more recently by the Global Positioning System. The primary phenomena of plate tectonics - sea-floor spreading and subduction -have thus been demonstrated beyond reasonable doubt for the various plates making up the Pacific Ocean (Lowman, 1996). Directly measured plate motions have proven surprisingly close to those inferred from the spacing of marine magnetic anomalies, covering about 3 million years (Stein, 1993). The space geodesy data will be shown in future editions of this map. However , the spreading rates calculated by Minster and Jordan (1978) are retained in this one.

These maps have proven effective in geologic education, and have been used in several textbooks. They are not subject to copyright and may be freely reproduced if the source is credited.

The following is a list of major recent references. For data sources of the original map, the reader is referred to Lowman (1981).

References

Bibliography: Publications using Tectonic Activity Map

*Books

Technical Papers, reports

*Exclusive of Lowman publications