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Tectonic/Volcanic Landforms

Tectonic landforms usually dominate the scenery in any region that has experienced significant crustal disturbances, and this activity often shows as truly spectacular expressions in remote sensing images. For this reason, the theme chapter by this title in "Geomorphology from Space" is by far the longest. These landforms frequently reveal surface manifestations of the type of underlying deformation caused by plate tectonic interactions. Some of these interactions characterize orogenic (mountain) belts at subduction zones (convergence of two or more plates) or pull-apart regions where plates diverge. For anyone unfamiliar with the first-order framework of the global tectonic system, examine this map produced by Paul D. Lowman, Jr. (author of Section 12) of the lithospheric plates, spreading ridges, transform faults, and other tectonic features. Consult any introductory Geology textbook for more information on the Plate Tectonic paradigm.

First-order framework map of the global tectonic system.

We described some exceptional examples of tectonic landforms in Sections 2, 6, 7 and 9, which you can review (look particularly at the Zagros folds and the Pindus thrust belts in Section 2 and the Appalachian folds and Basin and Range block fault mountains in Section 6). These paragraphs focused on folds and faults, the most common types of tectonic deformation. The resulting landforms commonly have elevation differences (relief) that may be sufficient to change ecosystems developed at these heights. Thus, mountains in a semi-arid climate may be heavily vegetated (dark toned in visible band images) and adjacent basins less so (light), thus, showing strong contrasts in black and white images (the Nimbus 3 image in Section 14 is a good example). Mountainous terrains appear clearly in Landsat and radar images by virtue of shadowing, which causes tonal variations related to slope/sun positions.

Because we already showed several examples of fold belts, we will only re-enforce this survey with one additional image, here in western Pakistan, showing part of the fold belt that came from the huge collision between the Indian subcontinent and southern Asia (the context of this is evident in the mosaic examined earlier in Section 7). The scene shows the Sulaiman fold belt, consisting of echelon (offset) anticlines (some closed), making up the ridges (flat valleys occupy intervening synclines). The Kingri fault passes through the image center (look for an abrupt discontinuity). The crustal block to its west (left) has moved northward relative to the block on the east.

Color image part of a fold belt in western Pakistan.


17-3: As a generalization, would you say that the "style" of deformation in the Anti-Atlas and Pakistan scenes is similar or dissimilar? ANSWER

To the west is the Arabian tectonic plate, caught between the African, Eurasian, and Indian-Australian plates as they move in different directions. The western part of this plate is a crystalline shield (a continental nucleus containing ancient igneous and metamorphic rocks). Below is a mosaic (from 12 individual Landsat scenes) of the shield as exposed in southern Saudi Arabia and the Yemen Arab Republic.

Color Landsat mosaic image of the crystalline shield in the Arabian tectonic plate.

A dominant feature in this scene is the numerous granitic intrusions, whose boundaries show as distorted oval shapes. The shield is a region of low mountains separated by valleys, many of which are sand-covered. A prominent escarpment (near the upper, left edge) bounds the western edge of the shield. The coastal plain is edged by a fault-controlled scarp. Another scarp (lower right) also relates to the fault.

17-4: Broadly speaking, how does the tectonic "style" of this Arabian Shield scene differ from that of the previous two images? ANSWER

Another remarkable mosaic covers much of northwestern Australia, a region of limited vegetation so that the rocks and valley-fill stand out and reveal much of their underlying structure. This is the Western Australian shield, containing mostly Precambrian metasedimentary and metavolcanic rocks, interlaced in places by igneous rocks. At the top of the mosaic is the Pilbara block, a leading candidate for the classic expression of an ancient greenstone-granite complex anywhere on Earth.

Color Landsat mosaic image of the Western Australian shield.
Color-coded geomorphic map of the Western Australian shield.

The granite appears as batholiths, up to a 100 km (62 mi) long. These light rocks are diapiric intrusions into the dark greenstones (metamorphosed basalt). To the south is the Hamersley Range (blue area on the map) and the smaller Opthalmia Range (red), bordered on the south by the Ashburton Trough (left) and the Bangemall basin (right). Low-relief hills mark much of the region. The highest area (1,235 m, 4,051 ft) is in the Hamersley Range.

17-5: The upper and lower half of the Australian mosaic are tectonically different. What might this difference be (tectonically)? ANSWER

Turning now to volcanic landforms, we show two images that represent two major types of volcanoes.

False color image of Mauna Loa on the Big Island of Hawaii.

On the top is the Big Island of Hawaii (see Sections 8 and 14 for other renditions). Mauna Loa is the central part of a huge shield volcano, which comprises the entire island. Its summit crater, a collapsed caldera named Mokuaweoweo, lies beneath a crest at 4,135 m (13,563 ft). Its base lies about 4,000 m (13,120 ft) below sea level, which makes it the tallest single mountain in the world (Everest, while higher, rises from the valleys of the Himalayas that are thousands of meters above sealevel, so its relief is less). Numerous lava flows (dark basalt), many extruded over the last few centuries, emanate from Mauna Loa. Mauna Kea, a crater on the north section of the island, is now extinct. But the most active volcano in the world, Kilauea, lies along the east side of the island and is visible here as a dark patch. This island is quite young, consisting of multiple layers of basaltic flows built up in the last one million years. Hawaii is the latest in a series of volcanic islands formed from melted lower crustal rocks as the Pacific plate moves northwestward over a fixed hot spot in the Earth's mantle. A newer submarine, volcanic complex, now forming southeast of Hawaii, will eventually surface and replace the Big Island as the center of activity.

B/W image of the stratocone Muria on the island of Java in the Indonesian archipelago.

Above is a segment of Java, the main island in the Indonesian archipelago, a prime example of an island arc terrane still evolving. In the midst of thick sequences of geosynclinal sediments are a series of large composite stratovolcanoes, developed from crustal melt induced by frictional heat, as the Indian-Australian plate dives in subduction below the southernmost extension of the Eurasian plate (see the tectonic map at the top of this page). The stratocone on the north peninsula near the Java Sea is Muria. The highest (2,910 m, 9,545 ft) volcano is the active Merapi, which stands out as the lower of two in the left center. To its right is Lawu. Six other large volcanoes are mainly to the west (left) of Merapi.

17-6: What is missing volcanically in the Java image that is present in the Hawaiian scene? ANSWER

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Primary Author: Nicholas M. Short, Sr. email:

Collaborators: Code 935 NASA GSFC, GST, USAF Academy
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