Volcanic Landforms (NLWv3)

Version 3 of the Named Landforms of the World (NLWv3) is an update of version 2 of the Named Landforms of the World (NLWv2). NLWv2 will remain available as the compilation that best matches the work of E.M. Bridges and Richard E. Murphy. In NLWv3, we added attributes that describe each landform's volcanism based on data from the Smithsonian Institution's Global Volcanism Program (GVP). We designed NLWv3 layers for two purposes: To label maps with broadly accepted names for physiographic features. To add landform attributes to other layers. For example, species observation data or other small features to enable rich and relevant descriptions for how those features relate to landforms. To accomplish this, typically, we use overlay tools such as Identity. For background, version 2 provided features with the physiographic and geomorphologic characteristics for the world's named landforms. This means it was more than just showing the land versus water or mountains versus plains; it also included the underlying structure and processes that created the landforms. We begin with the largest landform regions, which are continents, followed by tectonic plates, then divisions, provinces, sections, and finally, individual landforms. In adding the GVP volcanic landforms to NLWv3, we learned that volcanoes are relatively short-lived as landforms, with most not enduring for two million years. For context, the age of the rocks in most of the Earth's mountain ranges is in the tens to hundreds of millions of years. The full collection of layers and maps for NLWv3 are available in an ArcGIS Online Group named Named Landforms Of the World v3 (NLWv3) Layers and Maps. The GVP included two inventories--one for the Holocene Epoch, which are the volcanoes that formed during most recent 11,700 years (since the last ice age). The other is for the Pleistocene Epoch, which precedes the Holocene, and lasted about 2.6 million years. While the Pleistocene epoch is 222 times longer than the Holocene, it only has 7.8% more volcanoes. Most of the volcanoes that formed during the Pleistocene have disappeared through natural erosional and depositional processes. In NLWv3, volcanic landforms include calderas, clusters and complexes, shields, stratovolcanoes, and minor volcanic features such as cinder cones, lava domes, and fissure vents. Not all the GVP features, particularly fissure vents and remnants of calderas, are large enough to be mapped as polygons in NLWv3. Similarly, complexes and volcanic fields typically had greater areas and included many individual cinder cones and calderas. Continent Count of Volcanic Landforms Area km2 of Volcanic Landforms (% of land area) Europe 78 22,888 (0.23%) Antarctica 42 34,035 (0.27%) Australia 147 57,422 (0.65%) South America 370 81,475 (0.46%) Small Volcanic Islands 559 124,310 (8.52%) Africa 282 147,116 (0.50%) Asia 698 227,486 (0.53%) North America 622 295,340 (1.23%) Global Totals 2,798 1,000,073 (0.67%) This table shows the distribution of volcanic landforms and their surface areas. Overview of Updates Corresponding landform polygons now include attributes for the GVP's ID, name, province, and region. Details are provided below in the volcanic attributes section. Additionally, a text description of volcanism for each GVP feature was derived from these attributes to provide a reader-friendly characterization of each volcanic landform. Landforms of Antarctica. Given recent analysis of Antarctica and the use of GVP data, rudimentary landform features for Antarctica have been added. See details in the Antarctica section below. Refined the definition of Murphy's Isolated Volcanics classification. If the volcanic landform occurred outside of an orogenic, rifting, or subducting zone, only then did we consider it isolated. The areas along tectonic plate boundaries are where volcanoes typically occur. Only volcanoes occurring in areas with no tectonic activity are considered isolated. These typically occur in mid-continent or mid-tectonic plate. See details in the Isolated Volcanic Areas section. Edits to tectonic process attributes in selected areas. The GVP point locations for volcanoes include an attribute for the underlying tectonic process. The concept matched the existing tectonic process in the NLWv2, and we compared the values. When the values differed, we reviewed research and made changes. See details in the Tectonic Process section below. Minor boundary changes at the province, section, and landform level in the western mountains of North and South America. Details are provided below in the Boundary Change Locations section. Technical Characteristics The NLWv2 and NLWv3 are derived from the same raster datasets used to produce the 2018 version of the World Terrestrial Ecosystems (WTEs), which, when combined, have a lowest-common-denominator resolution (minimum mapping unit) of 1 km. Some features, such as very small islands, were not included in NLWv3, and complex coastlines were simplified and were only included if the 1-km cell contained at least 50% land. Because the coastlines in the raster datasets varied by as much as 3 km from the actual coastline, nearly always due to missing land. Many of the worst such cases in NLWv2 were manually corrected using the 12-30-meter resolution World Hillshade layer as a guide. In NLWv3, we continued this work by adding 247 volcanic islands, some of which were smaller than 1 km in area. We estimate that these islands comprise about one percent of the world's smaller islands. In NLWv3, we also refined the coastlines of volcanic coastal areas, particularly in Oceania and Japan. For NLWv4, we plan to continue this refinement work, intending that future versions of NLW will have a progressively refined, medium-resolution coastline. However, we do not intend to capture the full detail of the Global Islands dataset, which was produced from 30-m Landsat data. Detailed Description of Updates Volcanic Attributes The GVP Excel spreadsheets for the Holocene and Pleistocene epochs, which contained the coordinates and attributes for each volcano, were combined. A column for the geologic age was added before saving the spreadsheet as a .CSV file and importing into ArcGIS Pro. The XY Table to Points tool was used to create point features. Nearly ten percent of the point locations that lacked sufficient precision to fall within the correct landform polygon were revised manually in order to assign the correct Volcano ID to each polygon. 2,394 of the 2,662 GVP volcanic features were assigned to landform polygons. 198 GVP features were not assigned because they represented undersea features, and 75 GVP features did not have apparent corresponding landform polygons because they were either too small or indistinguishable from surrounding topography. This view layer was produced by filtering all landforms where the Volcano Name is not blank or an empty string. Of the 2,394 assigned GVP features, 48% are Holocene Age features and 52% are Pleistocene epoch features. 225 GVP features did not fall within within a landform feature that represented topographically a volcanic landform feature, such as a caldera or stratovolcano. This was usually due to insufficient precision of the GVP coordinates, which sometimes were rounded to the nearest integer of latitude and longitude and could therefore be over 50km away from the landform's location. Attribute Description Volcano ID (SI) The six-digit unique ID for the Global Volcanism Program features. Volcano Name (SI) The Name of the volcanic feature as provided by the Global Volcanism Program. Volcanic Region (SI) The Name of the volcanic region as provided by the Global Volcanism Program. Volcanic Province (SI) The Name of the volcanic province as provided by the Global Volcanism Program. Volcanism A consistently formatted description volcanism for the landform feature based on the age, last eruption, landform type, and type of material. This information was not consistently available from the Global Volcanism Program, and we used a Python script to determine the condition of the Global Volcanism Program"s data and then include whatever information was available. Antarctica Several recent analyses of Antarctica complemented the GVP point features. In particular, the British Antarctic Survey's 2019 Deep glacial troughs and stabilizing ridges unveiled beneath the margins of the Antarctic ice sheet show sufficiently detailed land surface elevation beneath the ice sheets to support identifying topographic landform classes. We georeferenced the elevation image and combined it with Bridge's geomorphological divisions and provinces to divide the continent into different landform polygons. Additional work is needed to make these landform polygons as rich and accurately defined as those in NLWv2. Isolated Volcanic Areas There are 333 Isolated Volcanic landforms in NLWv2. We intentionally expanded on Murphy"s map which could not show many of the smaller landforms and areas due to the 1:50,000,000 scale (poster sized map of the world). Murphy"s map only included isolated volcanic areas in three locations: north-central Africa, Hawaii, and Iceland. In NLWv2, we used the Global Lithological Map to identify several areas on each continent and used the example of Hawaii to include many other known volcanic islands. In most ways, Isolated Volcanics denoted geographic isolation from other mountain systems. NLWv3 includes 2,798 volcanic landform features, and 185 have been assigned Murphy's Isolated Volcanic structure class because they do not occur within a region with the tectonic process of orogenic, subduction, or rifting. These Isolated Volcanic landform features are located mostly in mid-tectonic plate regions of Africa, the Arabian Peninsula, and on islands, particularly in the southern hemisphere, with a few in North America and Asia. NLWv3 contains 2,603 volcanic landform features, occurring on all continents and on islands within all oceans. Tectonic Process The GVP data included a tectonic setting attribute that was compiled independently of the NLWv2 tectonic setting variable. When these differed, we reviewed and, if needed, updated the tectonic setting variable in the NLWv3. This also revealed several regions of landforms that required updates to the Structure class. These areas included Japan, northeast Asia, the Aleutian Islands, and Alaska. We independently verified these regions using Orogeny and Mantle Dynamics: role of tectonic erosion and second continent in the mantle transition zone, which indicated specific orogenic and subducting areas, disagreeing with our original assessment and the GVP attribution for tectonic setting. Tectonic Process Holocene Volcanic Features Pleistocene Volcanic Features None (Isolated) 77 97 Orogenic 329 497 Subduction Zone 639 655 Rifted Area 275 130 Boundary Change Locations The locations of GVP features proved useful in conjunction with the multidirectional hillshade layer as a basis to refine the edges of several of E.M. Bridges' geomorphological provinces - specifically only along the edges of volcanic landforms. NLWv2 boundaries were based on landform boundaries produced using the GMTED 2010 250-meter global elevation dataset. Therefore, landforms that were smaller than 10 square km were unlikely to be found and included. The multidirectional hillshade layer displays landforms at finer resolutions than 250-meters, allowing for substantially smaller landforms to be seen, including cinder cones and traces of caldera margins. In several cases in the Western Cordillera ranges of the Americas these smaller landforms extended many kilometers beyond NLWv2 province boundaries. These boundaries have been modified to completely include the volcanic features.