Hawai'i Physical Geography_ Kohala Waterfalls and Feral Relief_ GPH 112_ Intro to Phys Geography Lab

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Apr 3, 2024

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2/21/24, 8:48 PM Hawai'i Physical Geography: Kohala Waterfalls and Feral Relief: GPH 112: Intro to Phys Geography Lab (2024 Spring - A) https://canvas.asu.edu/courses/177445/quizzes/1332421 1/7 Hawai'i Physical Geography: Kohala Waterfalls and Feral Relief Due No due date Points 8 Questions 4 Time Limit None Instructions The geomorphology of a shield volcano (like Mauna Loa on the left) that turns into the wild feral relief created by erosion of that volcanic surface (like Kauai on the right that has only a tiny bit of the original dome shape) Mauna Loa - what Kauai once looked like. Kauai - little left of the original shield volcano Feral Relief (feral means 'gone wild'): Origins on the Big Island A wet tropical climate, basalt shield volcanoes, and time are the three ingredients needed to turn the dome-like surface of a volcano into a landscape of "feral relief". The features and imagery of feral relief are presented in the diagram below.

2/21/24, 8:48 PM Hawai'i Physical Geography: Kohala Waterfalls and Feral Relief: GPH 112: Intro to Phys Geography Lab (2024 Spring - A) https://canvas.asu.edu/courses/177445/quizzes/1332421 2/7 The oldest Hawaiian Islands (NE) have the most feral relief, like Kauai and Oahu. The youngest of the Hawaiian Islands (The Big Island) has the least feral relief. The Big Island is the best place for you to study how feral relief replaces the original dome shape of a shield volcano. QUESTION 1: WINDWARD/LEEWARD PRECIPITATION DIFFERENCES What is the difference in precipitation between the windward and rainshadow sides of the Kohala volcano for the two locations provided? These screenshots from the geovisualization should remind you of the helicopter ride up and over the Kohala volcano. Windward-side rains drive the development of feral relief on the Big Island. INSTRUCTIONS : You are given two locations at about the same elevation next to the deepest river valleys eroding into the two sides of Kohala: the west (rainshadow) side and the east (windward) side. Using Fast Travel to jump to each of these locations, write down the rainfall in millimeters. Then subtract the rainshadow precipitation from the windward side estimate the difference in rainfall. EXAMPLE : at the same elevation of about 1235 meters above sea level, the Rainshadow side: 20.0782 -155.7522 has a rainfall of 1222 mm

2/21/24, 8:48 PM Hawai'i Physical Geography: Kohala Waterfalls and Feral Relief: GPH 112: Intro to Phys Geography Lab (2024 Spring - A) https://canvas.asu.edu/courses/177445/quizzes/1332421 3/7 Windward side : 20.1221 -155.7194 has a rainfall of about 4006 mm Thus the difference in rainfall is 2783 mm. This is almost 110 inches of rain. Think about the implications of that much more rain and what it would mean for water pouring down the river channels on the side of volcano. QUESTION 2: PLUNGE-BASIN WATERFALL HEIGHT An important physical geography term is "knickpoint". It just means a waterfall (or a group of waterfalls or rapids). Niagara Falls is the classic example. Knickpoints are important here, because their "retreat" uphill is the way that the feral relief valleys grow towards the volcano summit. The sudden drop (in elevation) of water releases a lot of energy in the form of water turbulence. The turbulent water undermines the waterfall cliff, that then collapses. With each cliff collapse, the waterfall keeps moving uphill and the valley keeps growing up into the volcano. The plunge-basin waterfalls start at the coast, when water flows over a coastal cliff. Just try to picture a small stream flowing over the sea cliffs to the left, making a waterfall. As the waterfall "knickpoint" retreats into the center of the volcano, the stream valley continues to grow in length - eventually completely eliminating the original dome of the volcano. As some streams ate backwards into the volcano, they captured other streams, leading to greater erosion and growing into the large valleys we see today. INSTRUCTIONS : You are given two locations at the head of a feral valley on the Big Island. The first location is at the top of the waterfall(s). The other location is at the bottom of a single waterfall or sometimes a sequence of waterfall jumps. It is a lot more fun to Fast Travel to the top first. Then, jump your avatar down and locate the second spot manually (or you can Fast Travel again). Just write down the elevations and subtract the bottom elevation from the top elevation.

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