B-Lab Report 056 Hawaii Combined - All Versions-2
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School
University of South Florida *
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Course
2000
Subject
Geology
Date
Apr 3, 2024
Type
Pages
8
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Report 5-1 Laboratory Number Five: The Geology of Hawaii Name: Partners: Activity 5.1, The Landscape of Hawaii (10 Minutes)
O
BJECTIVE
: To familiarize yourself with the geography and landscape of the Hawaiian island chain, and to learn about its age-progression.
This activity uses the large 1:500,000-scale State of Hawaii, Principal Islands Shaded Relief Map and the 1:500,000-scale State of Hawaii, Principal Islands Topographic Map. 1.
There are eight principal islands in the Hawaiian chain, which increase in age toward the northwest. List the eight islands in order of age. List the youngest first: (4 points, ☆
) 1 2 3 4 5 6 7 8 1.
There are five volcanoes on the Big Island of Hawaii: Hualālai, Kīlauea, Kohala, Mauna Kea, and Mauna Loa
. Make sure you can locate them on the map. Which two are the highest? (2 points, ☆
) High volcano #1: High volcano #2: 2.
Which volcano is the oldest? (1 point, ☆
) 3.
Which volcano is the youngest? (1 point, ☆
) 4.
Based on the shape of the landscape, how many extinct volcanoes do you think are found on Oahu? (1 point, ☆
) 5.
Which volcano has steeper sides, Mauna Loa or Mauna Kea? (1 point, ☆
) Activity 5.2, Minerals of Hawaii (13 Minutes)
O
BJECTIVE
: To learn how to identify the four common minerals of Hawaii in hand sample: olivine, pyroxene, plagioclase, and magnetite.
NOTE: This activity must be done first, before any other rock or mineral activities in the laboratory. Box 1 contains pure specimens of the four minerals that are common in Hawaii: olivine
,
pyroxene
,
plagioclase
,
and magnetite
. Note that almost all of the magnetite found on Hawaii is microscopic. 1.
Examine the specimens carefully, and fill in the following table which summarizes their physical properties. When you are done underline the property or properties that you think will be most useful in identifying each mineral in hand sample. (3 points each, all ☆
) 2.
What additional property of magnetite makes it very easy to identify? (HINT: this is sort of like, “What food do they serve a
t Pizza Hut?”) (1 gift point,
☆
) Minerals of Hawaii, Activity 5.2 Cleavage? Hardness? Luster? Color? H-A1: Olivine H-A2: Magnetite H-A3: Plagioclase H-A4: Pyroxene
Report 5-2 Activity 5.3, Aphanitic, Phaneritic, Porphyritic (5 Minutes)
O
BJECTIVES
: To learn how to recognize aphanitic, phaneritic, and porphyritic texture in igneous rocks. This activity contains five rocks that aren’t from Hawaii, but which demonstrate the meaning of the terms aphanitic, phaneritic, and porphyritic. For each rock, check the appropriate boxes in the following table. (1 point each, all ☆
) Pick one! Porphyritic Aphanitic Phaneritic HU-1 HU-2 HU-3 HU-4 HU-5 Activity 5.4, Hawaiian Rocks (15 Minutes)
O
BJECTIVES
: (a) To learn how to recognize the important Hawaiian minerals in rocks; (b) To learn how to recognize basalt; and (c) To learn how to recognize the important textural features of volcanic rocks: aphanitic, phaneritic, porphyritic, and vesicular. In this activity, you will identify the common rocks found on Hawaii, without the aid of a microscope. Since all of these rocks are aphanitic volcanic rocks, your only reliable clue to the rock type will be in the phenocrysts. NOTE: You must also have completed Activities 5.2 and 5.3 before doing this activity. 1.
For each of the following five rocks, identify any visible minerals and name the rock (2 points each, ☆
). NOTE: Do not just list the minerals that might be found in the rock; list only those minerals you can identify in the rock with your naked eye or with the aid of a hand lens. Visible Minerals Rock Name HAW-1 HAW-2 HAW-3 Visible Minerals Rock Name HAW-4 HAW-5 2.
For the same rocks, check all that apply to the texture
of the rock: (1 point each, ☆
) Pick one! Porphyritic Aphanitic Phaneritic HAW-1 HAW-2 HAW-3 HAW-4 HAW-5 Activity 5.5, Thin Section #1 (6 Minutes
)
O
BJECTIVES
: (a) To learn how to recognize olivine in thin section; (b) To learn how to infer crystallization order from the texture of volcanic rocks, especially in thin section. NOTE: Activities 5.3 and 5.4 must be done before this activity. This activity uses a thin section of Rock HAW-1, a clastic rock from Mauna Loa Volcano on the Big Island of Hawaii. There are both a hand sample and thin section for this rock. You have already identified the minerals visible in hand sample for this rock in Activity 5.4. 1.
What is the major phenocryst in this rock? (1 point, ☆
) 2.
Examine the phenocrysts both in plain-polarized and cross-polarized light. Do they cleave or fracture? (3 points, ☆
) 3.
What birefringent colors do the principal phenocrysts display (i.e., grays, vivid, or washed-out)? (2 points, ☆
)
Report 5-3 Activity 5.6, Thin Section #2
(7 Minutes)
O
BJECTIVES
: (a) To learn how to recognize plagioclase in thin section; (b) to learn how to infer crystallization order from the texture of volcanic rocks, especially in thin section. NOTE: Activities 5.3 and 5.4 must be done before this activity. This activity uses a thin section of Rock HAW-2, from Kilauea Volcano on the Big Island. There are both a hand sample (Activity 5.4) and thin-section for this rock. 1.
The most abundant phenocrysts in this rock display gray birefringent colors. What mineral is this? (3 points, ☆
) 2.
The most prominent feature of these minerals is the presence of abundant polysynthetic twinning
that can be clearly seen in cross-polarized light. This twinning causes the crystals to appear “striped”. Are individual stripes always black or white, or do they change colors when the stage is rotated? (2 points, ☆
) 3. The pale yellowish crystals in the groundmass are pyroxene
. What is the order of crystallization of minerals in this basalt? Defend your answer. (2 points, ☆☆☆
) Activity 5.7, Thin Section #3 (4Minutes)
O
BJECTIVES
: (a) To learn how to recognize pyroxene in thin section. NOTE: Activities 5.3 and 5.4 must be done before this activity. This activity uses a thin section of Rock HAW-3, collected from the north side of the volcano Haleakala on the island of Maui. HAW-3 contains pyroxene phenocrysts. Pyroxene looks
somewhat similar to olivine, but can be distinguished by a pale green or brown color in plain-polarized light
. Olivine is clear in plain-polarized light. Also, the presence of cleavage may sometimes cause the pyroxene to appear “fibrous” in thin section. What birefringent colors does pyroxene exhibit? (4 points, ☆☆
) EXTRA CREDIT: The groundmass of HAW-3 contains pyroxene, plagioclase, and glass. The plagioclase appears as clear needles in plain light, while the pyroxene displays higher birefringence. The glass is nearly opaque due to the presence of magnetite inclusions. Based on the texture of this rock, what was the order of crystallization? Make sure you include the magnetite. Defend your answer. (3 points, ☆☆☆
) Activity 5.8, Thin Section #4 (7 Minutes)
O
BJECTIVES
: To learn how to recognize volcanic glass in thin section. NOTE: Activities 5.3 and 5.4 must be done before this activity. This activity uses a thin section of Rock HAW-4, which comes from Kilauea Crater on the Big Island of Hawaii. It is a piece of a recent lava flow, probably erupted in the past 100 years. 1.
Notice the material that is green in plain-polarized light. Is this material opaque, isotropic, or anisotropic? (3 points, ☆
) 2.
What is this material? (2 points, ☆
) Activity 5.9, All Kinds of Beaches (12 Minutes)
O
BJECTIVES
: (a) To review the identification of the principal Hawaii minerals in hand sample and thin section; To review the sediment properties of sorting and roundness as applied to Hawaiian beach sediment.
NOTE: You must complete Activities 5.2-5.8 before you can start this activity.
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Report 5-4 Hawaii is justly famous for its beaches, which are some of the most beautiful and variable in the whole world. In this section you will examine beach sands from Hawaii and determine what they are made of and how they formed. The three beach sand samples can be examined as: (a) loose sediment that can be examined with a hand lens or with the magnifying microscope; and (b) thin sections of sand grains dispersed in an epoxy medium.
Complete the table on the top of this page, which summarizes the appearance, mineralogy, and textures of the three beach sands based on an examination of the loose sediment and thin sections. For glass, also describe the color of the glass in plain light (i.e., “pale brown glass”) in the column “Mi
nerals observed”. For roundness and sorting, use the charts found inside the cover of your laboratory manual. (4 points each, all ☆
) Activity 5.10, Summary of Hawaiian Rocks
(10 Minutes)
O
BJECTIVE
: To learn the relationship between igneous rock composition, rock type, and included minerals.
NOTE: Activities 5.1 through 5.9 should be complete before you do this activity. There are no rocks or maps to examine; just discuss the answers with your partner. Use your Igneous Rock Calculator to help you answer the following questions.
1.
Pyroxene is a very common mineral in Hawaiian rocks, though it is usually restricted to the groundmass of rocks and is therefore difficult to observe in the field. However, one of the best ways to identify minerals in rocks is based on association with other minerals. What other minerals does your Igneous Rock Calculator tell you should be associated with pyroxene in igneous rocks? (2 points, ☆
) 2.
Fill in the following table based on your Igneous Rock Calculator. (1 point, ☆
) Note that magnetite may also occur in any
rock (igneous, sedimentary, or metamorphic) so its presence doesn’t really help to identify the rock (but we’ve included it anyway so you
remember it’s there).
Basalt Gabbro Magnetite Magnetite 3.
What is the essential difference between a gabbro and a basalt? (1 point, ☆☆
) 4.
Would you expect to see pyroxene + quartz in an igneous rock? Why or why not? (2 points, ☆☆
) Pyroxene + quartz? Why or why not?
Beach sands of Hawaii, Activity 5.9 Sand Color of loose sediment Roundness of sand grains Sorting of sand grains Minerals observed (including glass), and percentage of each HBS-1 HBS-2 HKS-1
Report 5-5 Activity 5-11, Xenoliths in Hawaiian Lavas
(7 Minutes)
O
BJECTIVES
: (a) To learn how to recognize plutonic igneous rocks; (b) To learn about xenoliths, and why they occur.
In your first two laboratories you studied the geology beneath Florida. Since Florida is such a flat state, with very few rock exposures, it was necessary to use driller’s reports and cores to examine the rocks underlying Florida. In this laboratory, we are also interested in rocks buried deep under the ground, but in this case the rocks are so deep that they cannot be obtained by drilling (except at great and prohibitive expense). Instead, geologists take advantage of the natural ability of magmas to drag pieces of the surrounding rock up with them when they erupt to sample and interpret the rocks beneath Hawaii. As you have read, these pieces are called xenoliths
. Rock HAW-6 was collected from Puu Haiwahine, a cinder cone on the western flank of Mauna Kea. You will not be responsible for pronouncing Puu Haiwahine, but you should be familiar with Mauna Kea! 1.
Examine the hand sample of HAW-6 and notice that it contains both a xenolith and its host lava. In the table below, place a checkmark in each box that applies for both the xenolith and its host lava. (2 points, ☆
) Lava Xenolith Pick one Aphanitic Phaneritic Porphyritic Vesicular 2.
List all the minerals you can identify in the xenolith with your naked eye: (3 points, ☆
) 3.
What is the name of the lava rock
? (1 point, ☆
) 4.
What is the name of the xenolith
? (1 point, ☆
) EXTRA CREDIT: Now look at the thin section of HAW-6. Does this sample contain magnetite? Does it appear to be associated with any of the minerals in this thin section, and if so
–
which one? (3 points, ☆
) 5.
Rock HAW-7 was also collected from Puu Haiwahine. This is another small xenolith and is also quite crumbly
–
so be super extra careful with it. Identify the minerals in this xenolith, along with their proportions. Make sure the percentages add up to 100%. (3 points, ☆
) Mineral Percentage 6.
What kind of rock is the xenolith? (2 points, ☆
) EXTRA CREDIT: Does this rock represent magma that has solidified, or does it represent crystals that have been extracted from magma and solidified? Explain your answer!!! (It’s a big difference. In the former case, you could remelt the rock and reproduce the original magma. In the latter case, you can’t
). (5 points, ☆☆☆
)
Report 5-6 Activity 5-12, Earthquakes on the Hawaiian Islands (15 Minutes)
O
BJECTIVES
: (a) To learn how to read and interpret a seismicity map; (b) To learn why earthquakes form in Hawaii
. Study the map Seismicity of Hawaii, 1962-1985. This beautiful map shows the locations of significant earthquakes that occurred in the Hawaiian Islands over a period of 23 years. In addition to showing the distribution of earthquakes, the map is also a color-coded topographic and bathymetric map. 1.
What do the different size circles represent on this map? (2 points, ☆
) 2.
What is the evidence from this map that most earthquakes in the Hawaiian Islands are associated with active volcanoes, and aren’t just randomly distributed? (2 points, ☆☆
) 3.
Does this evidence necessarily mean that the earthquakes are caused by magma moving
–
or could there be another explanation for their association with volcanoes? Explain. (3 points, ☆☆☆
) Now look at the map Earthquake Map of South Hawaii, 1968-1981 It is a much more detailed map of a smaller area than the previous map, and only shows earthquakes on the southern part of the Big Island of Hawaii. 4.
What do the different colored symbols on this map correspond to? (2 points, ☆
) 5.
If you read the map text carefully, you will find that the earthquakes around Kilauea volcano indicated with red symbols are associated with magma movement during eruptions. Notice that these earthquakes are not restricted to the summit area but also occur widely over two swaths called rift zones
. Using earthquakes, can you trace these rift zones to the edge of the island? Beyond it? (3 points, ☆☆
) 6.
If these rift zones are areas where lava frequently erupts, what should they look like? Should they be hills? Ridges?
Basins? Valleys? (3 points, ☆☆
) EXTRA CREDIT: Locate the same rift zones on the Seismicity of Hawaii, 1962-1985 map by observing the color-coded topography. Do they extend to the edge of the island or beyond it? What does this imply about eruptions on Hawaii? (3 points, ☆☆☆
) Activity 5.13, Water on the Hawaiian Islands: Rain and Groundwater (15 Minutes)
O
BJECTIVE
: To learn how orographic rainfall occurs, and how it falls on the Hawaiian Islands. To learn how groundwater occurs on volcanic islands like the Hawaiian Islands.
Rainfall data for the Hawaiian Islands are summarized in a United States Geological Survey (USGS) Professional Paper entitled Summary Appraisals of the Nation’s Ground Water Resources
–
Hawaii Region (PP:813-M). 1.
Look first at the distribution of rainfall on the Big Island (page M7), the island with the highest mountains. Notice that rainfall isn’t equally distributed; which side is the wet side? (2 points, ☆
) 2.
Now examine the rainfall distribution for Kauai (page M7), which is a much older, eroded, and lower island. How is rainfall distributed on Kauai? How does it compare with the Big Island? (2 points, ☆
) EXTRA CREDIT: Where is the wettest place on the Hawaiian Islands? (1 point, ☆
) EXTRA CREDIT: Approximately how many inches fall there, on average per day? (1 point, ☆
) 3.
The distribution of rainfall on mountainous islands is due to the deflection of moist ocean winds by the high mountains, as described in Figure 5 on page M8. Hawaii
lies in the trade wind belt, a region of the earth in which strong,
steady
winds blow most of the time. As these winds travel across the open ocean, they absorb water and become very humid. When the trade winds reach Hawaii, they are deflected
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Report 5-7 upward by the mountains. The moist air then rises, and as it rises it cools down. (This cooling is due to something called the
adiabatic lapse
rate
, but it’s not important to remember that term. All you need to remember is what your experience already has instructed you: that as you go higher in elevation, it gets colder. That’s why it snows in the mountains.) When the air is cooled, it loses its ability to retain all the moisture it once held, and the moisture comes out in the form of rain. This rainfall is called orographic
rainfall
. Based on the maps of rainfall distribution, from what direction do the trade winds in Hawaii blow? (2 points, ☆
) 4.
According to the orographic model, it begins to rain when the air cools to a certain temperature, determined by its elevation. At what elevation does most of the rain fall? You can determine this by looking at the distribution of rainfall and comparing it to the topography of the Hawaiian Islands, or by studying Figure 5 carefully. (3 points, ☆
) EXTRA CREDIT: Based on the distribution of rainfall alone, where would be the best place on the Big Island to develop a resort? (Remember, tourists do not like to sit on the beach in the rain). (1 point, ☆
) Groundwater data for Hawaii are summarized in another part of USGS Professional Paper Summary Appraisals of the Nation’s Ground Water Resources–
Hawaii Region (PP:813-M). 5.
Based on the distribution of rainfall on the islands, which two Hawaiian Islands do you think have the least groundwater? (2 points, ☆
) 1. 2. 6.
Figure 9 on page M15 shows the nature of groundwater reserves and withdrawals on the Big Island of Hawaii. Which of the three major sources of fresh water (dike-impounded water, perched groundwater, and basal groundwater) do the major supply wells tap? (2 points, ☆
) 7.
How many regions of dike-impounded water can be identified on the Big Island of Hawaii? What do they correspond to? (2 points, ☆
) EXTRA CREDIT: Based on the distribution of dike-impounded groundwater, do you think Mauna Kea volcano has well-developed rift zones like Mauna Loa and Kilauea? Defend your answer. (2 points, ☆☆
) EXTRA CREDIT: Figure 12 on page M18 shows the nature of groundwater reserves and withdrawals on the island of Oahu. Oahu is the most populous island in the Hawaiian chain, and is home to the capital city of Honolulu. There are many water supply wells on Oahu that tap into the dike-impounded groundwater reservoir. Why is this a more viable option on Oahu than on the Big Island of Hawaii? Explain your answer. HINT: Think about population density and elevation. (3 points, ☆☆
)
Report 5-8