Preliminary Field Trip Lab: Geomorphology of Southwestern New Hampshire GLS100 Geomorphology Lab Dr. Lindley S. Hanson, Dept. of Geological Sciences
This lab is to familiarize you with the area we will be studying during our class field trip.
Goal
To illustrate how the geomorphology of southwestern New Hampshire reflects past and present geologic processes, and to understand how basin geomorphology influence stream hydrology.
Objectives
Following completion of this lab you will are expected to be able to:
1. read and interpret topographic maps: Identify ridges and valleys and general topography 2. describe the major tectonic terranes of New Hampshire and Massachusetts 3. learn the difference between terrain and terrane 4. read and interpret hydrographs graphs 5. make and record observations: Identify sediments and processes in the field, make detailed descriptions, field sketches, etc. 6. relate the relationship runoff, baseflow, and stream discharge to basin drainage basin morphology and geology. 7. Use Google Earth’s measuring tool and topographic map overlays to gather profile data 8. construct profiles and measure gradients from topographic maps 9. identify and interpret glacial deltaic deposits from topographic maps 10. measure area, perimeter and length using ImageJ 11. know the terms and concepts emphasized in this lab
Lab Requirements 1. Colored Pencils 2. Google Earth (http://earth.google.com/download-earth.html).
Note: you should use the latest version of the software, available from the link above. If you have not used Google Earth before, take a few minutes to familiarize yourself with its capabilities. It is essentially a user-friendly GIS package that patches together aerial photography for the entire globe and outer space (some areas with better resolution than others) with topographic and other geographic information. It has limited but useful analytical tools. You can zoom
1 in and out of locations, rotate images, and change the tilt angle to provide 3- dimensional views of topographic features. You can enter locations in the search window to the left, and navigation tools are available in the upper-right of the image. Extensive on-line help is available for the program, and I can help get you started with some of the basics, if necessary. For this lab and other to follow you will be requested to download and load KMZ files that contain all the required location markers, profile lines and links to maps. The file will load in your temporary places and will be moved to
3. ImageJ (http://rsbweb.nih.gov/ij/) ImageJ a Java application used for image processing. Download and install the application and become familiar with the basic components of the toolbar and the Analyze menu command. You must have the ability to right click on your computer to take advantage of the range of tools.
Introduction to the Geology of Southwestern New Hampshire
Part I: Bedrock Geology
New England is a jigsaw of accreted lithotectonic terranes accreted to the margin of Proto-North America (Laurentia) during the Paleozoic Taconic and Acadian orogenies. Through convergence and docking of these terranes the Northern Appalachians were constructed during the Paleozoic Era. Traveling from east to west the terranes that we will visit are:
1. Avalon Terrane: A mirocontinent cored by 600 ma basement that attached to North America during the Devonian. Contains Precambrian through Cambrian metasedimentary rocks and a variety of Precambrian through Devonian igneous and volcanic rocks. This terrane underlies the North Shore. You’re familiar with this block— we live on it and studied some of its rocks on the Forest River Field Trip.
2. Central Maine Terrane (Kearsarge-Central Maine Synclinorium): composed of metamorphosed and highly deformed marine sediments scraped off the Iapetus ocean basin that separated and eventually subducted beneath Avalon and Laurentia during the Devonian Acadian Orogeny. This tectonic block contains Silurian continental margin deposits overlain by easterly-derived Siluro-Devonian foredeep turbidites shed from the approaching Avalon Microcontinent. This highly metamorphosed package was transported westward and folded into a complex series of nappes, portions of which we will see on Mount Monadnock.
3. Bronson Hill Terrane (Bronson Hill Anticlinorium) An ancient volcanic arc welded to North American during the Ordovician Taconic Orogeny. It contains metamorphosed Late Ordovician calc-alkaline volcanic rocks (Ammonoosic Volcanics) overlain by a carapace of related sedimentary and volcanic rocks (Partridge Formation). The eroded arc is unconformably draped by the Silurian continental shelf sediments
2 (Fitch and Clough formations) and Devonian Flysch. Alstead and South Acworth are located in the Bronson Hill Terrane.
On Saturday we will be working in the Bronson Hill Terrane. On Sunday we will climb Mount Monadnock (3,165 ft) located in the Central Maine Terrane.
Figure 1. Tectonic map of New England showing tectonic terranes and location of field trip area. From Wintsch and others (2002).
During the early-Acadian Orogeny (420-385 ma) these terranes experienced thrust faulting, were deformed into west-verging nappes, and intruded by syntectonic plutons, such as the Kinsman and Bethlehem granites. Continued deformation back-folded these structures into east-verging nappes that were domed and penetrated by the remobilized Ordovician Oliverian plutons of the ancient arc. These mantled gneiss domes characteristic of the Bronson Hill Anticlinorium were created during this last phase. (The Alstead Dome, visible from your campsite is such a dome.) Tectonic thinning and subsequent erosion of the Appalachians followed Acadian deformation.
3 Normal faulting and unroofing (tectonic thinning) accompanied relaxation and rifting of the orogen during late Paleozoic and Mesozoic periods. Continued erosion and glaciation during the Cenozoic added the final touches to the landscape we see today. The total amount of erosion can be roughly estimated from metamorphic mineral assemblages suggesting pressures greater than 4 kb. Because 1kbar ± 2 miles we can reasonably estimate that we are at an erosion depth of ~8 miles. The original sedimentary cover was entirely removes revealing a variably resistant terrain of crystalline metamorphic and meta-igneous rocks. With the exception of the upper 100 feet or so, all of this erosion was preglacial. Glaciers during the Pleistocene (1.8 ma-10ka) simply smoothed or streamlined hill crests, covered slopes with ground moraine (till), and filled valleys with ground moraine and glacial-fluvial melt-water sediments.
Figure 2. Jim Thompson's (1954) original map and cross section of local area. Since his original work 3 additional nappes and several thrusts have been identify yielding an even more complex structure (Robinson and others, 1991).
Residual Hills - Monadnocks
Although New England was quite active tectonically during the Paleozoic and Mesozoic, the present landscape is the result of erosion. Under such conditions the relative strength of the rocks exert a powerful influence on landscape. Mount Monadnock is composed of the same Devonian turbidites we mentioned in part IIB in your first lab. However, these turbidites were a bit more proximal and contained thicker beds of sandstone. The combination of a high-grade granoblastic metamorphic texture and higher quartz content have made the rocks forming this mountain quite resistant, as is towers over the adjacent
4 lowlands. Their horizontal structure may add to the mountains prominence. William Morris Davis, who promoted the fluvial cycle of landscape development, defined a monadnock as a residual hill resting on a peneplain--an erosional surface reduced to baselevel. Originally Davis believed that monadnock were random remants, but later admitted that they were probably composed of more resistant rock—thereby being the result of differential erosion of the peneplain surface.
Part II: Glacial Geology and Hydrology
During the Pleistocene Epoch continental ice sheets flowed into southwestern New Hampshire at least twice. Although the marine record illustrates several glacial advances over the last 1.8 million years, multiple glacial episodes are not evident in this area (Jack Ridge, Personal Communication). Nevertheless, an interglacial paleosol between tills exposed in the Boston Harbor drumlins provides documented evidence of two glacial advances through New England. Until otherwise proven, all till and glacial-fluvial deposits visited during our trip are assigned to the last stage of glaciation known as the late-Wisconsinian, and were the product of the Laurentide Ice Sheet.
Glacial Lake Hitchock Valleys often become temporarily dammed during deglaciation by a tongue of ice, or a dam of glacial debris left in the valley. Glacial lakes are evidenced by a variety of deposits that include varved clays, laminated silts, and flat delta plains composed of sand and gravel. The well-drained surfaces of glacial deltas make great sites for landing strips or airports, and cemeteries. There are also an important source of sand and gravel and make good aquifers. G.K. Gilbert first defined the structure of lake deltas, while investigating the pluvial lakes in the Basin and Range. These Gilbert-type deltas are composed of a three part sequences (fig. 3) that grades upward from fine to coarse:
1. bottomset beds: fine-grained laminated beds formed in deep water
2. foreset beds: dipping beds of sand and gravel formed by the avalanching of grains down the delta front
3. topset beds: fluvial beds of gravel and sand deposited by streams transporting sediment to the delta front
5 Figure 3. Components of a Gilbert-type delta, typically deposited in glacial lakes.
The elevation of the foreset-topset disconformity defines the level of the lake to which the delta was graded. Glacial geomorphologists use ancient glacial lake surfaces to determine variations in post-glacial rebound and thickness of the ice sheet. The rate of depression by the ice-sheet and subsequent rebound was about 4 feet (1.3 m) per mile extending from the ice margin (coastal area) to its source in Northeastern Canada.
The largest glacial lake in New England was Glacial Lake Hitchcock in the Connecticut Valley. Dammed by a moraine in Middleton Connecticut the lake progressively lengthen as the ice retreated northward reaching a length of 184 miles and lasting nearly 4000 years (Stone and Others, 1998, and references therein). Longevity of the lake was aided by flexural downwarping of the valley near northward-retreating ice margin. When the Middleton dam failed a lower lake developed until glacial rebound revived the valley's south-dipping gradient.
Eskers, deltas, drumlins and other glacial landforms have distinct morphologies that can be readily identified on a topographic map, provided the scale is not too small. A good surficial geologist will locate features on a map before going into the field.
6 Pre-Field Trip Laboratory Exercises
Exercise I: Glacial Lake Hitchcock
Open the SWNH KMZ file and load it into Google Earth. Included are topographic overlays of the field trip area. Look at the map in figure 4 and activate the Alstead topomap layer in Google Earth.
1. Study the topography around the Connecticut Valley shown below. Describe any evidence indicating the presence of a glacial lake.
2. On the map below, color the area occupied by Glacial Lake Hitchcock.
Figure 4. Topographic Map of the Connecticut Valley near Bellows Falls, VT.
7 3. Locate the broad delta plain east of the lower reach of Mountain Brook and north of the Cold River. If the foreset-topset contact is 5 feet below the delta surface, what was the elevation of the lake (relative to present-day sea level) during the time of deposition? ______ft
4. Do you think this represents the actual elevation of the lake during deposition? If not explain why.
5. There are a couple of flat terraces located at lower elevations. a) Propose one or more hypotheses explaining the origin of these terraces, and b) discuss how you would test them.
8 Exercise 2: Geomorphology and Hydrology . Stream channel characteristics and hydrology are strongly influence by the glacial sediments covering their drainage basins. Ground moraine (till) is highly impermeable where as glacial-fluvial sediment are permeable. The relative amount and distribution of these sediments with influence the amount of runoff and baseflow, and the subsequent stability of stream flow. In the last 12,000 post-glacial streams have incised the glacial deposits filling their valleys. We will focus on the drainage basin of the Cold River, a west-flowing tributary of the Connecticut. A principle tributary of the Cold River is, Warren Brook, the site of a devastating flood October 9, 2005. We will investigate the conditions leading to the flood during class and, observed the changes caused by the flood and subsequent reconstruction efforts in the field.
The Cold River has a drainage area of 110 square miles and includes 11 tributary basins. Data for each basin is shown below. (fig. 1., and Table 1) Excluding some minor ice-contact deposits (eskers and kames) most of the basin east of Alstead is underlain by ground moraine (till).
Figure 2. Cold River and its tributary basins. From Kelly (1983).
9 Drainage Ad Mean Main Main Basin relief Basin (mi 2) Annual Q Channel Channel (ft) (cfs) length (mi) slope (ft/mi)
1 Underwood Brook 1.62 2.47 2.8 164 941
2 Dodge Brook 10.8 26.5 6.2 48 1030
3 Honey Brook 2.9 4.5 2.8 180 790
4 Bowers Brook 5.8 9.1 4.7 185 990
5 Milliken Brook 2.9 4.5 3.7 227 980
6 Great Brook (Acworth) 7.4 12 5 175 1000
7 Crane Brook 2 3.17 4 259 1049
8 Warren Brook 20.8
9 Darby Brook 5.1 8.1 3.7 222 1210
Cold River (Drewsville) 82.6 118 20.2 47 1706
10 Great Brook (Langdon) 15.3 24 9.9 5 1443
11 Mountain Brook 1.8 2.8 3.1 222 849
Cold River at mouth 110 182 23.6 48 1840
Table 1. Mean Annual Flow (water year 1983) and drainage basin parameters for the Cold River and its sub-basins. (modified from Kelly, 1987)
Exercise II: Runoff, Baseflow and Hydrographs
Warren Brook (basin #8 on map) is a southwest flowing tributary of the Cold River. Both streams tend to be flashy, characterized by low low-flows in the summer and high peak-flows during storms or extended periods of precipitation. Their behavior is intricately tied to the geology and geomorphology of their drainage basins.
10 Figure 4 is an annual hydrograph of the Cold River created from data taken at the Cold River gage at Drewsville (1983-84). This plot is constructed by plotting the mean daily flows.
Look at the graph and answer the following questions: (Be careful, discharge is plotted on a logarithmic scale.)
1. What is the peak flow for this period in cubic feet/sec (cfs)? ______
2. What is the lowest flow in cfs? ______.
3. By convention these graphs are plotted on semilog paper. Why?
As shown in figure 4, you can separate the peak flows from an undulatory base. This base represents the groundwater contribution, or baseflow, to the river, while the separated peaks represent the runoff. Notice the seasonal fluctuation of baseflow and runoff. This is due to seasonal variations in evapotranspiration and precipitation.
Answer the following questions:
1. Geomorphologists are very much interested in the materials composing a landscape, and can infer much about surface materials from drainage density and the hydrology of streams. For example, we can conclude from the hydrograph that most of the Cold River Drainage Basin is underlain by impermeable glacial till and rock, rather than the permeable deltaic deposits seen near in and around the Connecticut valley. How? Explain the relationship between runoff, baseflow and permeability.
11 2. What other factors will also influence the relative proportion of baseflow and runoff?
3. The annual baseflow contribution for the Cold River fluctuates around 43% of the total flow at the Drewsville gauge. However, the baseflow in the basin east of Alstead is lower (<25%). Revisit Exercise I and propose a hypothesis as to why this might be true.
4. Using Excel quickly make a log-log plot of drainage area (X) and discharge (Y). Draw a best-fit line to the data and explain the relationship. How can this plot be used to predict the flow of ungauged streams.
5. How would you expect the graph to vary for an arid region? Explain.
On October 8-9, 2005 Southwestern New Hampshire was hit with approximately 10-12 inches of precipitation causing widespread flooding. Along scenic Warren Brook a torrent of water over 12 feet high sweep through the town of Alstead just before 7:00 am on October 9th. Twenty-nine houses were destroyed and four people were killed. Kmiec's Garage, a cement block and concrete building located near the confluence of Warren Brook and the Cold River, was swept away along with dozens of cars and the station’s underground gas tanks. Adding to the damage was the removal of a large section of Route 123 that followed the brook up to Lake Warren.
The U.S. Geological Survey (USGS) estimated that the peak flow of the Cold River at the Dyersville gauge, located about 2 miles downstream from the town of Alstead, and was 21,800 cubic feet per second (cfs). The mean annual streamflow at that point is typically around 100 cfs. Gauge height peaked at 23.7 feet, doubling the previous recorded maximum of 12.3 at a flow of 6,700 cfs (Mrazik and Foster, 2005). The October 2005 flood is considered to have a 500-year recurrence interval (Flynn, 2006). The extreme flooding was related to high precipitation, previously saturated antecedent conditions, failure of a blocked culvert (see map), and drainage basin characteristics. Basin characteristics that influence flooding are:
1. Composition of the drainage basin: A basin underlain by impermeable glacial till and bedrock would promote runoff.
2. Slope: A high percentage of steep slopes will increase runoff velocities and reduce residence time on the ground thereby inhibiting infiltration.
3. Shape of the basin and distribution of tributaries: A rounded basin with a dendritic pattern is more prone to flooding than an elongate basin with a trellis-type distribution of tributaries.
12 4. Drainage Density: (sum of all tributary lengths/basin area) This characteristic shortens the path that water has to travel before entering a stream. A higher drainage density promotes flooding.
Exercise 3: 2005 Warren Brook Flood
Google Earth is great for viewing landscapes and measuring distances but does not measure area, unless you buy the $600 version. For this reason we are going to take an image that I created and save in Google Earth and import into ImageJ for analysis. We will measure some morphometric features that will help us characterized the drainage basin and quantify characteristics that promote flooding. Follow the steps below to determine the perimeter and area of the drainage basin and length of the stream. Record the values below.
Step I: From WebCT download the WarrenBrook.jpg. Step II: Open ImageJ and go to file>open, locate the image and load it. Step II: Zoom in on the image so you can clearly see the bar scale (2.05 miles between tic lines) Step IV: Select the line tool in the tool bar. Carefully draw a line between two tic lines then go to the menu and select Analyze>set scale. Type in the known distance (e.g. 2.05) and the unit of length (miles). On a separate piece of paper record the distance in pixels and the known distance. If your measurement seems off base chances are the scale was altered. When that happens simply return to Analyze>set scale and retype the numbers. Step V: In the toolbar select the polygon tool and outline the drainage basin. Once completed, adjust the line for accuracy. Then select Analyze>measure to get the area and perimeter of the basin. Step VI: Measure the length of Warren Brook. In the toolbar right click the line tool to select segment line. Draw the line along the length of the stream and measure.
Note: 1. Press the space bar and drag the image in order to scroll while drawing. To right click on a Mac Book Pro place fingers on the track pad and click (but it must be enabled – instructions) 2. Use Ctrl+D key commands to make the line permanent.
Record and complete the following:
1. Perimeter of Warren Brook Drainage Basin: ______miles 2. Area of Warren Brook Drainage Basin: ______square miles 3.Length of Warren Brook from the mouth to the tip of the longest tributary: ______miles
13 4. Approximately what percentage of area is covered by slope? ______
5. From the map determine the basin's maximum relief? ______Calculations: Highest point in the basin______- Lowest point in the basin = ______
6. Determine the average gradient of Warren Brook. Calculations: ( Highest point on the Brook _____ - Lowest point on the Brook)/stream length _____ = ______feet/mile
7. Using the techniques learn determine the gradient of Warren Brook along the reach between Warren Pond and the Cold River. ______
8. Complete the Table 1 by filling in the data for Warren Brook.
9. Flood discharge in Warren Brook during thee 2005 flood. Given are the following conditions: Warren Brook flowed through a 6’ diameter culvert beneath Cooper Hill Road (by Forstall Corner), a secondary road built on a 30-foot-high earth-filled embankment that filled the valley. Obstruction of the culvert caused the broad valley upstream to fill with water forming a temporary lake. When water started flowing over the road, the embankment failed sending a powerful flood surge into the populated valley.
From the following information calculate the flood discharge: The area of the temporary lake is shown in blue on the Warren Brook image. Assume an average depth of 11 feet. If it took 15 minutes for the impoundment to drain following failure of the culvert what would be the flood discharge (cfs) down the valley? ______(There are 5280 ft in a mile) Calculations:
10. Elongation ratio (Er) is a dimensionless number (<1) dependent on a basin's shape (figure 6) and is calculated using the following equation: Er= DA /DL where: DA is the diameter of a circle equal to the area of the drainage basin: DA =2(A/3.1416).5) DL is the maximum length of the basin
a. Determine the elongation ratio for Warren Brook. ______b. Basin Area______c. Basin Length ______
14 d. Figure 6 shows how the flood hydrograph varies for two similar basins with different shapes. Think how basin shape effect flooding and offer an explanation.
Figure 6. Two drainage basins with different shapes and different responses to a storm. The unit hydrographs illustrate how each stream response to a single storm event. The elongation ratio is low for A and high for B.
In summary; The intense rainfall of October 5-6, 2005 on a naturally flashing drainage basin coupled with poor planning and maintenance of a local culvert resulted in 500-year flood for this area.
15 Exercise 4: Mount Monadnock
Before climbing a mountain it’s nice to know what you’re in for. So we are going to do a little preliminary study of the mountain and the trail. In Goggle Earth activate the topographic overly of Mount Monadnock and the White Arrow Trail, and answer the following questions:
1. Determine the length of the hike in miles: ______2. Determine the vertical change in elevation along the trail: _____ 3. What is the gradient from the base to the Hermitage: ______4. What is the gradient from the Hermitage to the top: ______5. Are you likely to get your feet wet on the trail? ______If so where and why?
6. Are there any features visible from the map that might indicate that Mount Monadnock was covered by glacial ice? Discuss if your answer is yes.
You are now ready to do a little field exploration!
16 References
Allen, Tim, Nappes, 19 , Gneiss Domes and Plutonic Sheets of West-Central New Hampshire: in Timothy W. Grover, Helen N. Mango, and Edward J. Hasenohr, editors, Guidebook to Field Trips in Vermont and Adjacent New Hampshire and New York, New England Intercollegiate Geologic Conference, 89th Annual Meeting, p. A2.1 - A2.19.
Chamberlain, Page C., and Lyons, J. B., 1983, Pressure temperature and metamorphic zonation studies of pelitic schists in the Merrimack Synclinorium, south-central New Hampshire: American Mineralogist, v. 68, p 530-540.
Flynn, R.H., 2006, Flood study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005: U.S. Geological Survey Open-File Report 2006-1313, 48 p.
Kelley, Edward, F., 1987, Surface water hydrology of the Cold River, Southwestern New Hampshire: Master's Thesis, Boston University, Boston, MA, 156 p.
Olson, Scott, 2006, Flood of October 8 and 9, 2005, on Cold River in Walpole, Langdon, and Alstead and on Warren Brook in Alstead, New Hampshire, Federal Emergency Management Agency Open-File Report 2006–1221,U.S. Department of the Interior U.S. Geological Survey 46 p. (pdf)
Mrazik, Brian, and Foster, Debra, Oct. 18, 2005, Updated October 2005 Flood Data for New Hampshire and Vermont, USGS News Release, http://nh.water.usgs.gov/What'sNew/newsreleases/flood101805.htm
Stone and others, 1998, Quaternary Geologic Map of Connecticut and Long Island Sound Basin: U.S. Geological Survey Open File Report OF 98-371.
Thompson, J. B., Jr. (1954) Stratigraphy and structural geology or the Skitchewaug Mountain area, Claremont quadrangle, Vermont-New Hampshire: New England Intercollegiate Geological Conference, 46th Annual Meeting, Hanover, New Hampshire, Guidebook, p. 93-174.
Thompson, Peter J., 1985, Stratigraphy, Structure and Metamorphism in the Monadnock Quadrangle, New Hampshire: Ph.D. thesis, Contribution no. 58, Department of Geology and Geography, University of Massachusetts, Amherst, MA, 119 p.
Thompson, Peter J., 2001, Geology of Mount Monadnock: in West, David P., Jr., and Richard H. Bailey (eds.), Guidebook for Field Trips in New England, 2001 Annual Meeting of the Geological Society of America, Boston, Massachusetts, p. R1-17.
17 Wintsch, R. P., Kunk, M. J., Boyd, J. L., and Aleinikoff, J. N., 2003, P-T-t Paths and differential Alleghenian Loading and uplift of the Bronson Hill Terrane, South Central New England: Amer. Jour. Scien., v. 303, p. 410-446.
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