Writeup Instructions: For this lab, you will take a MULTIPLE CHOICE QUIZ. In the Submit Labs area, simply click the appropriate lab quiz, follow instructions, and answer the 20 multiple choice questions. All quizzes will be somewhat different because questions are randomly selected from a large data base. You can repeat the quiz if you wish, I will keep the highest grade.
When you take the quiz, I recommend that you use two open windows: one for the quiz and one open to this lab so you can look up information. I am not asking you to memorize anything and there is no time limit on the quiz.
Purpose: This lab introduces some of Hawaii's basic landforms and helps you to recognize them visually.
IMPORTANT! In the Fluvial and Coastal Landform sections below, images pop-up when the cursor is placed over the blue-linked landform names. You will probably need to disable your browser's pop-up blocker to see the images. Also, avoid clicking the image; if you do, the lab instructions page will jump to the top and the image will disappear behind it.
Hawaii Landforms includes a combination original fluvial and coastal geomorphology lessons and resources provided by Volcano World. On the quiz, you will be shown images of 20 of the following landforms, chosen at random. (Some images will be different than those presented below.) All you have to do is identify them. Before taking the quiz, be sure that you have gone through all of the material and can recognize all of the landforms. While taking the quiz, you should have two windows open, one open to the quiz and the other open to this Lab so you can compare quiz images with the material given in the Lab. NOTE: some of the images on the quiz will be new, but comparable to those shown in the following landform descriptions.
|Volcanic Landforms||Fluvial Landforms||Coastal Landforms|
Review the volcanic landforms lessons provided by Volcano World for Hawaiian Volcanism. Click the links at the right for lessons on Large Scale Features, Vents, Lava Flows, and Lava Transport.
Fluvial refers to the work of water, which is responsible for most of the erosional shaping of the surface of Hawaii's shield volcanoes. Geologists have identified a gradual erosion life cycle, which is illustrated below (from Macdonald et al., 1983)
In the initial youthful stage (A and B), streams carve well spaced, steep-sided, V-shaped valleys separated by wide flat expanses of the original shield volcano surface such as seen along the Hamakua coast of the Big Island. Notice the narrow stream channels identified by the dark green strips of trees. On volcanic islands, streams headwaters radiate out from the center of the island in a radial drainage pattern. Often the stream channels form a stepped course with plunge pools at the base of high waterfalls. As the topography matures, the upper reaches of stream-cut valleys also converge, with one valley often becoming the dominant water conduit in a process called stream capture. In the image, Waipio Valley has captured the headwaters of Waimanu Stream on the slopes of Kohala Volcano. The aging valleys grow into the familiar wide amphitheater-headed valleys such as Manoa. As the valley heads converge toward the center of the island, they isolate triangular sections near the coast called planezes, as illustrated in B above and seen on the house-covered slopes above East Honolulu. Notice how the houses rise up the flat planeze of Waahila Ridge to a triangular apex, after which a narrow ridge divides the upper (and converging) valleys of Manoa and Palolo.
In the mature erosion stage (C and D above) the flat planezes completely wear away, such as seen in the image of the eastern end of the Koolau range. As erosion continues, spectacular knife ridges form in the wet interiors separating "vertical valleys." The original valley walls eventually disappear leaving only the fluted valley headwalls and retreating ridges presiding over relatively flat terrain such as southeast Kauai (Lihue area). As the islands flatten out, the erosional work of the ocean becomes a more dominant shaping force.
Hawaii's surrounding ocean hammers relentlessly at the coastline, carving away a bit of the islands with each wave until, ultimately, it completely erases the aerial basalt of extinct volcanoes. As wave erosion shrinks the islands, it creates distinctive landforms. Windward shores feel the brunt of the ocean's assault and here erosional forces work most quickly to plane away the rock, leaving a notched coastal shape, as shown below.
The wave-cut nip forms at the shoreline under the most intense wave action. Anyone who has walked to the Toilet Bowl at Hanauma Bay has touched a wave-cut nip. The windward shore of Niihau gives an excellent example of sea cliffs with an offshore wave-cut terrace, which is visible as an offshore reef platform. Occasionally, these platforms may become exposed, perhaps due to falling sea level, and form flat coastal plains of old coral reef. In the image, you can clearly see the sea cliffs that mark the old coastline of Mana plain, west Kauai. Because the coastal rock differs in its resistance to erosion, an exposed headland may form, jutting out from the retreating adjacent coastline (note the Molulua sea stack in the background). This focuses wave energy to undercut the rock behind the headland which may carve a sea arch, such as this one in Volcanoes National Park. Small offshore islands, created by the collapse of a sea arch or simply isolation by erosion, are called sea stacks. Famous sea stacks of offshore Oahu include Mokoli'i (Chinaman's Hat) and the Mokuluas of Lanikai.
The erosion of the coastline pulverizes rock and coral into sand, which forms deposits both along the shoreline (beaches) and offshore (sometimes visible as sandbars). Hawaii's beaches change shape with the season and weather as sand moves both onshore and offshore and laterally with currents. In general, high wave energy gouges a steep beach face and moves sand offshore, while low wave energy forms a gently sloping beach face and moves sand back onto the beach. Beaches shape changes continuously as in this image showing the excavation of Kailua beach by high wave action. Inland from the beach face, a high berm typically forms which is the beach equivalent of a transverse dune found deserts. Individual beaches may be confined by rocky headlands with a high resistance to erosion. At the mouth of rivers and canals, the sand may close the channel completely forming a bay-mouth bar. The outgoing water simply filters slowly through the sand to escape to the ocean during normal conditions, but may open to the ocean during periods of high stream flow (or dredging).
As the waves plane the exposed basalt, they create broad wave-cut terraces on which the reefs grow. In Hawaii, all of the reefs are classified as fringing reefs, even though in some areas, such as Kaneohe Bay, they may extend two miles offshore. As the aerial rock erodes, it eventually shrinks to a few rocky pinnacles sitting on a submerged platform, such as the Gardener Pinnacles, Necker Island, and Nihoa Island northwest of Kauai, and then disappears completely. The reef continues to grow, however, on the broad flat platform left by erosion forming atolls, such as Midway and others in the northwest Hawaiian Islands. In Hawaii, the chain of atolls extends to about 30 degrees north latitude as shown in the map below. North of that, the water is too cold for corals to grow and the flat, coral-capped former islands sink beneath the waves forever as guyots. The entire sequence is animated in this Life of an Island movie created by Bishop Museum.
Most volcanic landform images from USGS
V-shaped valley, Waimanu, Big Island (http://www.webcom.com/trw/hawaii/contents.html)
Hamakua Coast (http://www.webcom.com/trw/hawaii/contents.html)
Stream Capture, Big Island (http://volcano.und.nodak.edu/vwdocs/hawaii_review/life_stages/post_alkalic/kohala1.html)
Planeze, East Honolulu (instructor)
Stage C, eastern Koolaus (http://soswcd.org/images2.htm)
Knife Ridge, windward Oahu (http://www.photolib.noaa.gov/coastline/coind9.htm)
Vertical Valley, windward Oahu (http://satftp.soest.hawaii.edu/space/hawaii/virtual.field.trips.html)
V Shapel Valley, Waimanu (http://polihale.com/display/60117/2)
Stage D, windward Oahu (http://satftp.soest.hawaii.edu/space/hawaii/virtual.field.trips.html)
Plunge Pool, Akaka (http://www.matuschek.net/vacation/hawaii2002/gallery/index.html)
Plunge Pool, Rainbow Falls (http://www.hawaiiweb.com/hawaii/html/sites/rainbow_falls.html)
Sea Cliffs, Niihau (http://polihale.com/display)
Sea Cliffs, Molokai (http://satftp.soest.hawaii.edu/space/hawaii/vfts/molokai/molokai.air.photographs.html )
Sea Arch, Volcanoes NP (http://www.terragalleria.com/parks/np.hawaii-volcanoes.2.html)
Coastal Plain, Mana, Kauai (http://polihale.com/display)
Wave-cut Nip (instructor)
Wave Face (instructor)
Sea Stack (instructor)
Bay-mouth Bar (instructor)
Berm, Big Beach, Maui (http://www.mauistore.com/picture_pages/big_beach_in_makena.htm)
Gardener Pinnicles (http://explorers.bishopmuseum.org/nwhi/picarch.shtml)
Midway Island (http://www.hawaiianatolls.org/maps/satimages.html)
Life Stages of Islands (http://www.hawaiianatolls.org/teachers/lesson_life_of_an_island.html)
Macdonald, G.A., Abbott, AT, Peterson, FL (1983) Volcanoes in the Sea, 2nd Ed., UH Press