The influence of slope aspect on soil weathering processes in the Springerville volcanic field, Arizona

Catena 43 Ž2001. 49–62 www.elsevier.comrlocatercatena

The influence of slope aspect on soil weathering processes in the Springerville volcanic field, Arizona Jason A. Rech a,) , Richard W. Reeves b, David M. Hendricks c a

Department of Geosciences and Desert Laboratory, UniÕersity of Arizona, 1675 W. Anklam Road, Bldg. 801, Tucson, AZ 85745, USA b Department of Geography and Regional DeÕelopment, UniÕersity of Arizona, HarÕill Bldg. Box 2, Tucson, AZ 85721, USA c Department of Soil, Water, and EnÕironmental Science, UniÕersity of Arizona, Shantz Bldg. a38, Tucson, AZ 85721, USA Received 25 November 1999; received in revised form 4 April 2000; accepted 5 April 2000

Abstract A comparison was made between soils on north- and south-facing slopes of six cinder cones in the Springerville volcanic field ŽSVF., Arizona, in order to determine the influence of slope aspect on soil weathering processes. Twenty-four soil pedons were sampled on different aspects of six cinder cones. To control for the influence of slope on pedogenesis, all sample sites possessed slopes of 17 " 28. Soil weathering processes were characterized by solum depth, texture, and Ca:Zr chemical weathering indices. Quartz and mica were used to identify eolian additions to the volcanic soils. Accelerated rates of weathering and soil development were found to occur in soils on south-facing slopes while no trend with aspect was found for eolian additions. Accelerated rates of weathering and soil development may influence cinder cone degradation and cone morphology. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Chemical weathering; Cinder cones; Dust; Slope aspect; Volcanic soils

1. Introduction Landform degradation results from the breakdown and removal of material by several earth surface processes. The type and abundance of vegetation, the amount of soil )

Corresponding author. Tel.: q1-520-629-9455 ext.108; fax: q1-520-792-8819. E-mail address: [email protected] ŽJ.A. Rech..

0341-8162r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 4 1 - 8 1 6 2 Ž 0 0 . 0 0 1 1 8 - 1

50

J.A. Rech et al.r Catena 43 (2001) 49–62

moisture, and the particle size of hillslope sediments all influence the nature of mass movements and the erodibility of hillslope material. Since landforms outside the tropics receive different amounts of insolation on north and south-facing slopes, weathering and hillslope denundation processes may also occur at different rates on opposing slopes. The central portion of the Springerville volcanic field ŽSVF., located in east-central Arizona Ž; 338N., contains over 150 cinder cones. Most of these cinder cones are asymmetrical with gentle south-facing slopes and steep north-facing slopes. Reeves Ž1996. calculated slopes for the entire population of cinder cones in the central portion of the field from digital elevation models and has found that the steepest facets of north-facing slopes Žazimuth between 3458 and 158. have an average inclination of 22.38, while the steepest facets of south-facing slopes Žazimuth between 1658 and 1958. have an average inclination of 18.58. This asymmetrical morphology is either a primary feature of these cinder cones or the result of differential weathering and erosion after formation. Porter Ž1972., for example, postulated that strong prevailing easterly winds during eruption produced the asymmetrical morphology of cinder cones on Mauna Kea Volcano, HI. Since the SVF does not experience consistently strong winds from a uniform direction, the asymmetrical morphology of the cinder cones is likely the result of differential weathering and erosion. Differential weathering is likely influenced by differences in temperature and moisture content between slopes, while erosion rates will be influenced by vegetation type and cover, particle cohesion, cryogenic turbation of the soil, and duration of snow cover. Cinder cones have been widely studied by geomorphologists to estimate rates of erosion and soil development ŽScott and Trask, 1971; Wood, 1980; McFadden et al., 1986; Dohrenwend et al., 1986; Renault, 1989; Hooper and Sheridan, 1998.. Cinder cones form by deposition of scoria around a volcanic vent. This process produces features that are initially similar in morphology, generally symmetrical with flanks inclining at the angle of repose, easily erodable, and dateable by a variety of geochronological techniques. Since cinder cone fields usually contain several hundred cinder cones of various ages, they represent a natural laboratory for studying rates of soil development, erosion, and landform denundation. Cinder cones degrade over time by a variety of surficial processes. The importance of soil development to decreasing the permeability of cinder cone surfaces and generating overland flow has been postulated by Wood Ž1980. and Renault Ž1989.. This research explores the possibility that either accelerated soil weathering environments or increased dust deposition rates on south-facing exposures create finer textured soils than on north-facing slopes. Either of these scenarios could influence degradation processes and ultimately cone morphology. There have been several studies on the influence of slope aspect and the resulting microclimate on weathering and soil development ŽCooper, 1960; Finney et al., 1962; Klemmedson, 1964; Fanzemier et al., 1969; Davis, 1976; Losche et al., 1970; Macyk et al., 1978; Daniels et al., 1987a,b; Carter and Ciolkosz, 1991.. All of these studies attempt to isolate the influence of microclimate by controlling other soil forming factors. The difficulty with this is in isolating a single variable, microclimate, and attributing all differences in pedogenesis to that variable. Previous studies have compared soils that developed on different lithologies or on slopes of different inclinations, either of which

J.A. Rech et al.r Catena 43 (2001) 49–62

51

will influence soil formation. Another shortcoming of some studies is the small population of samples, sometimes as few as 4–8 pedons. In general, however, higher mean annual soil temperatures, approximately 28C, can be expected on south-facing slopes, while a higher moisture content can be associated with north-facing slopes in the northern hemisphere ŽCooper, 1960; Fanzemier et al., 1969.. Several studies ŽCooper, 1960; Finney et al., 1962; Fanzemier et al., 1969; Losche et al., 1970. found more advanced stages of soil development on south-facing slopes. In these studies, accelerated pedogenesis was attributed to increased weathering resulting from warmer temperatures, increased freeze–thaw cycles, or increased wetting and drying cycles. In contrast, others ŽMacyk et al., 1978; Daniels et al., 1987a,b; Carter and Ciolkosz, 1991., attribute thicker solums and higher clay concentrations on northfacing slopes to increased soil moisture and illuviation. There are several reasons for the disparate results among the previous studies on the relationship between slope aspect and soil development. One is the inherent problem in attempting to isolate one factor in a pedosequence. Another issue is that the influence of slope aspect on weathering is environment specific, and therefore one relationship can not be generalized for the entire Northern Hemisphere.

2. Methods 2.1. Study area The SVF, which covers approximately 3000 km2 , is one of the largest basaltic cinder cone fields in the western United States and is located in east-central Arizona ŽFig. 1.. Condit et al. Ž1989a,b, 1994, 1995. and Crumpler et al. Ž1994. have identified over 375 cinder cones in the SVF. All volcanics in the SVF have been dated to - 3.1 Ma, based on thirty 40 Kr40Ar dates, 90 magnetic polarity reversal records, and stratigraphic relationships ŽCrumpler et al., 1994.. The detailed mapping of cinder cone age and lithology makes this an excellent area to study the influence of slope aspect on soil weathering processes. The SVF ranges in elevation from approximately 1820 m in the western portion of the field to nearly 3000 m at the summit of Greens Peak ŽFig. 1.. This difference in elevation produces a variety of climatic conditions and soil types. Climate stations at McNary Ž2235 m. and Springerville Ž2150 m. record an average annual temperature of 88C for both stations. McNary receives 70 cm of precipitation annually while Springerville, which is located northeast of McNary, receives 25 cm annually. The majority of this precipitation occurs during the summer months. The disparity in annual precipitation results from a pronounced rainshadow effect as moist air masses move from the southwest to the northeast ŽSellers and Hill, 1974, p. 486.. Significant influences on soil weathering environments in the SVF include the abundance of summer precipitation, annual snow cover, and the number of annual freeze–thaw cycles. The great range in elevation and climatic conditions in the SVF produces several vegetation zones. Today, oakrjuniper woodlands dominate between 2100 and 2600 m

52

J.A. Rech et al.r Catena 43 (2001) 49–62

Fig. 1. Location of Springerville volcanic field and the six cinder cones sampled in this study. Vent number, age, and cone mineralogy from Condit et al. Ž1994.. Map adapted from Crumpler et al. Ž1994..

and include ponderosa pine Ž Pinus ponderosa., gambel oak Ž Quercus gambelii ., alligator bark juniper Ž Juniperus deppeana., and Douglas fir Ž Pseudotsuga menziesii .. Elevations above 2800 m are dominated by sprucerfir forest, consisting of Englemen spruce Ž Picea engelmannii ., white fir Ž Abies concolor ., Douglas fir Ž P. menziesii ., limber pine Ž Pinus flexilis ., corkbark fir Ž Abies lasiocarpa., and quaking aspen Ž Populus tremuloides. ŽDavis, 1976.. There are also several areas of grasslands and cienagas above 2600 m. These are dominated by mountain muhly Ž Muhlenbergia montana., pine dropseed Ž Sporobolus cryptandrus., carex Ž Carex spp.., Arizona fescue Ž Festuca arizonica., Kentucky bluegrass Ž Poa pratensis ., June grass Ž Koeleria cristata., and mutton grass Ž Poa fendleriana. ŽDavis, 1976; Kearny and Peebles, 1951.. A conspicuous feature of this area is that many of the cinder cones above 2700 m have grassland-covered south-facing slopes and forested north-facing slopes ŽFig. 2..

J.A. Rech et al.r Catena 43 (2001) 49–62

53

Fig. 2. View of Greens Peak cinder cone from the southeast in March 1995. Photograph illustrates the significant differences in the amount of insolation received by south Žleft. and north-facing slopes, as well as differences in vegetation and albedo.

2.2. Methods Six cinder cones were selected to investigate the influence of slope aspect and vegetation on soil weathering environments ŽFig. 1.. Three cones Žcones 1–3. have grass-covered south-facing slopes and forested north-facing slopes and are located above 2700 m, while three cones Žcones 4–6. are forested on all exposures and located between 2250 and 2600 m. These two sets of cones were selected to encompass the variety of vegetation cover and climatic environments in the SVF. A total of 24 soil pedons, located on the north, north–northeast, south, and south–southwest aspects of each cone, were excavated. Pedons were located on these aspects to maximize the difference in microclimate. In order to control the influence of slope on soil development, pedons were generally located midslope at an inclination of 17 " 28. Soil samples were collected at a depth of 10 cm from all soil pedons and from 1 m depth from most pedons, except where bedded cinders or well-indurated argillic horizons were encountered - 1 m below the surface. In the latter cases, soil samples were collected at the cinder–soil contact or from the deepest location in the soil pit. One to three additional samples, depending on characteristics of each pedon, were also collected between 10 cm and 1 m. Soil morphology and pedon descriptions were based on texture, color, structure, and pH. X-ray fluorescence was used to determine elemental concentrations. Concentration of elements at 10 cm, 1 m Žor deepest sample., and from

54

J.A. Rech et al.r Catena 43 (2001) 49–62

parent cinders of all pedons was determined in the laboratory by a Spectrace 9000 field-portable X-ray fluorescence analyzer. A Phillips Electronic Instruments XRD-3000 was used for X-ray diffraction analyses of bulk soil, crushed cinder and clay samples. The pH of samples was determined with the 1:2 soil:water ratio method with a Beckman 11 combination pH electrode. Particle size was determined by the pipette method.

3. Results and discussion The representative pedon for midslope soils on young cinder cones Ž- 1 Ma. in the SVF is approximately 1 m thick and rests upon a bed of relatively unweathered cinders. The soil typically has a silty loam texture with - 10% clay, ; 60% silt, and ; 30% sand. On grass-covered soils there is a well defined A horizon overlying a cambic Bw horizon, or if there has been sufficient clay translocation, a Bt horizon. On forested sites there is a gradual transition between the A and the Bw or Bt horizon, which overlies unweathered cinders. The typical soil pedon on older cones Ž0.97–1.67 Ma. is similar to the younger cinder cone soils, but contains between 10% and 20% clay. Contrary to expectations, the youngest cinder cone sampled Žcone 6, 0.48 Ma. hosted the best developed argillic horizons, containing between 30–60% clay on all exposures. This illustrates that the age of the cinder cone does not determine the age of the soil. 3.1. Soil morphology There are several major differences in soil morphology between soils on north-facing and south-facing slopes on the six cinder cones sampled in the SVF. Solum depth is deeper on south sides of cinder cones than on north sides. Bedded cinders or welded pyroclastic material occur less than 1 m from the surface on seven of 12 north-facing profiles, while only one of 12 south-facing soils contain bedded cinders within 1 m of the surface. Finer- textured soils are found on south-facing aspects, with clay and silt percentages slightly higher on south-facing exposures ŽFig. 3A.. Surface horizons on north-facing aspects exhibited lower pH values than those on south-facing aspects ŽFig. 3B.. Table 1 displays cation abundance, particle size, and pH for all 10-cm and 1-m soil samples, as well as cation abundance for unweathered cinders at depth. Differences in pH of surface horizons between north-facing and south-facing aspects is likely the result of contrasts in microclimate and vegetation. Wetter conditions on north-facing aspects facilitate greater leaching, while the preponderance of spruce and fir trees Žcones 1–3. on north-facing slopes add more acidic organic matter to the soils than do grasses. 3.2. Weathering ratios Weathering ratios were used as a means of quantitatively differentiating weathering environments on north and south-facing slopes of cinder cones. Weathering ratios in soils are based upon the relative abundance of mobile cations in the soil environment,

J.A. Rech et al.r Catena 43 (2001) 49–62

55

Fig. 3. Average soil texture and pH for each aspect Žtotal of six pedons per aspect.. Clay, silt, and sand percentages are weighted with depth. Average pH values are from a depth of 10 cm.

e.g. Na, K, Mg, and Ca, to relatively immobile cations such as Fe, Al, Ti, and Zr ŽBirkeland, 1999, pp. 66–74.. As a soil becomes more weathered, mobile cations are removed and immobile cations increase in relative abundance. Weathering ratios are typically calculated for surface horizons of soils, and then compared to the underlying parent material. In order for these ratios to be meaningful, however, there must not be any additions of immobile and mobile cations used in the weathering ratios to the soil. Additions of elements not used in the weathering ratios, however, will not influence these indices. For example, additions of eolian quartz to the soil will not change the relative proportion Žratio. of a mobile element to an immobile element. Variations in the concentration of five elements at 10 cm and within parent material were used to assess the suitability of these elements for weathering indices. Fig. 4 shows the concentration of these elements, two mobile ŽCa, K. and three relatively immobile ŽFe, Ti, Zr., in the surface horizons Ž10 cm. as compared to parent material Žunweathered cinders at depth. at each pedon. Analysis of the parent material at each pedon

J.A. Rech et al.r Catena 43 (2001) 49–62

56

Table 1 Soil cation concentrations, particle size and pH Pedon Ždepth.

Fe Žppm.

Ca Žppm.

Ti Žppm.

K Žppm.

Zr Žppm.

C1-S 10 cm C1-S 1 m C1-S cinder C1-SW 10 cm C1-SW 1 m C1-SW cinder C1-N 10 cm C1-N 88 cm C1-Ncinder C1-NE 10 cm C1-NE 60 cm C1-NE cinder C2-S 10 cm C2-S 1 m C2-S cinder C2-SW 10 cm C2-SW 1 m C2-SW cinder C2-N 10 cm C2-N 1 m C2-N cinder C2-NE 10 cm C2-NE 90 cm C2-NE cinder C3-S 10 cm C3-S 55 cm C3-S cinder C3-SW 10 cm C3-SW 75 cm C3-SW cinder C3-N 10 cm C3-N 1 m C3-N cinder C3-NE 10 cm C3-NE 1 m C3-NE cinder C4-S 10 cm C4-S 85 cm C4-S cinder C4-SW 10 cm C4-SW 1 m C4-SW cinder C4-N 10 cm C4-N 1 m C4-N cinder C4-NE 10 cm C4-NE 88 cm C4-NE cinder

54,097 72,640 69,879 59,448 68,299 71,115 64,457 64,501 64,789 53,532 62,871 59,082 75,464 85,745 83,636 69,365 81,625 79,135 65,331 80,427 72,743 75,494 75,596 70,549 74,983 74,675 69,713 75,536 81,211 80,949 64,188 81,775 72,000 59,176 77,895 78,120 61,349 67,769 59,388 55,969 58,731 52,829 62,427 69,642 63,407 66,172 70,087 62,625

14,182 14,586 34,216 24,734 29,239 39,055 29,765 41,493 39,654 29,745 45,894 44,305 21,047 26,537 50,298 26,908 35,777 51,580 22,683 39,852 56,036 26,646 43,110 38,904 45,259 47,158 61,195 21,338 19,507 61,804 28,013 54,331 63,756 34,385 35,985 67,186 35,783 41,301 56,559 30,473 39,772 45,007 30,980 37,754 42,693 32,808 39,405 57,844

8817 12,178 11,317 10,173 11,985 12,274 11,391 11,530 10,635 9803 11,337 9665 15,659 18,142 18,164 14,367 17,526 17,005 11,783 16,808 14,677 15,341 17,388 15,703 14,594 14,624 13,208 13,768 14,507 15,570 11,900 16,690 13,117 10,745 16,208 15,636 12,171 14,031 12,356 9488 10,785 9562 12,080 15,544 13,669 13,257 15,655 13,481

21,599 20,540 21,442 13,993 10,550 7569 12,940 9577 9734 15,822 11,262 14,679 14,197 9576 8309 14,002 4985 4156 14,820 8012 6659 10,578 7551 7259 12,460 10,731 9444 16,886 11,315 11,575 16,078 11,955 11,667 15,440 11,381 7778 13,795 7070 12,100 14,624 12,968 13,887 10,442 4701 5241 11,487 6911 8520

306 356 335 343 370 353 348 289 291 302 295 274 295 318 290 319 330 260 267 292 274 307 313 273 265 289 259 322 335 264 252 230 222 249 373 259 255 248 215 304 320 254 254 271 259 293 269 252

Clay Ž%.

Silt Ž%.

Sand Ž%.

pH

5 6

68 50

27 44

5.89 6.43

4 4

73 56

23 40

6.50 6.99

4 1

55 75

41 24

6.53 6.29

9 5

71 48

20 47

5.72 6.12

4 7

64 66

32 27

6.60 7.20

5 4

54 40

41 56

5.82 6.88

7 3

56 39

37 58

5.20 6.18

4 1

54 40

42 59

5.67 6.01

4 7

42 40

54 53

6.27 7.56

12 29

59 46

29 25

6.31 6.88

7 4

56 23

37 73

5.20 5.84

3 3

71 42

26 55

5.40 5.68

6 16

64 54

30 30

6.92 6.71

15 14

55 38

30 48

5.90 6.81

8 15

60 59

32 26

5.65 5.84

9 13

59 50

32 37

5.39 6.23

J.A. Rech et al.r Catena 43 (2001) 49–62

57

Table 1 Ž continued . Pedon Ždepth.

Fe Žppm.

Ca Žppm.

Ti Žppm.

K Žppm.

Zr Žppm.

Clay Ž%.

Silt Ž%.

Sand Ž%.

pH

C5-S 10 cm C5-S 75 cm C5-S cinder C5-SW 10 cm C5-SW 70 cm C5-SW cinder C5-N 10 cm C5-N 75 cm C5-N cinder C5-NE 10 cm C5-NE 75 cm C5-NE cinder C6-S 10 cm C6-S 75 cm C6-S cinder C6-SW 10 cm C6-SW 70 cm C6-SW cinder C6-N 10 cm C6-N 72 cm C6-N cinder C6-NE 10 cm C6-NE 75 cm C6-NE cinder

76,688 69,700 80,701 75,546 60,994 70,186 75,108 75,280 76,850 80,664 81,907 79,676 70,253 80,366 70,355 69,046 67,657 66,405 86,146 78,371 69,883 84,655 83,139 67,496

25,973 38,690 61,247 23,449 25,031 56,953 37,755 62,336 65,193 32,482 47,573 63,209 17,948 26,322 59,173 24,828 24,038 52,153 18,663 39,884 65,377 17,843 27,624 64,181

13,364 11,042 14,443 13,952 8885 11,728 13,050 13,576 14,573 14,969 15,759 15,240 12,618 12,890 11,669 11,862 10,081 10,720 13,430 13,479 11,631 13,561 13,317 11,868

17,169 10,497 12,499 19,157 9971 8838 12,970 6411 8113 13,548 5675 4150 18,769 6361 5822 22,488 13,462 12,630 17,821 4850 6740 18,296 5937 5432

244 189 188 283 168 181 218 185 168 227 229 194 249 280 236 303 232 230 329 261 237 351 271 222

18 26

54 30

28 44

6.83 7.08

15 50

62 29

23 21

6.38 6.86

11 12

44 12

45 76

5.56 6.46

15 25

50 28

35 47

6.01 6.65

15 29

67 46

18 25

6.62 6.99

12 48

56 25

32 27

6.49 7.39

17 34

47 39

36 27

6.99 7.39

16 40

55 37

29 24

6.35 6.80

precludes problems associated with assuming parent material homogeneity. Results show that these soils are enriched in potassium, likely by eolian processes and possibly due to some recycling of potassium by vegetation. The concentration of calcium decreases substantially in surface soils as a result of weathering. There is no pedogenic carbonate in these soils, which would interfere with weathering indices, and any pedogenic carbonate added to soils by dust likely readily leaches through soils due to the wet, acidic conditions. Concentrations of immobile cations ŽFe, Zr, Ti. in soil and parent material identified Zr to be the least mobile, since ZrsoilrZrpm ) 1 ŽFig. 4.. Ca:Zr ratios were used to quantify soil weathering environments since they appear to be the most mobile and immobile elements, respectively. Ca:Zr ratios at 10 cm and 1 m Žor deepest sample in pedon. were compared to those in the underlying parent material. Fig. 5 displays the average ŽCarZrsoil .rŽCarZrpm . for both 10-cm and 1-m soil samples. Both 10-cm and 1-m average Ca:Zr ratios identify greater weathering in soils on south-facing slopes and greater weathering near the surface than at depth. 3.3. Eolian influence on soils Eolian dust makes major contributions to some soils, especially in the southwest USA ŽGile et al., 1981; Machette, 1985.. In basaltic terrains, eolian input can often be

58

J.A. Rech et al.r Catena 43 (2001) 49–62

Fig. 4. Mobility of the five cations measured. Values significantly )1 indicate additions to soil, values -1 indicate losses, while values close to 1 indicate immobility.

Fig. 5. Average Ca:Zr weathering ratios for 10 cm and 1 m soil samples. Lower average ŽCarZrsoil .rŽCarZrpm . ratios indicate greater chemical weathering while a value of 1 would indicate no weathering.

J.A. Rech et al.r Catena 43 (2001) 49–62

59

identified by the presence of extralocal minerals, such as quartz and mica ŽRex et al., 1969; Dymond et al., 1974; Graham and Franco-Vizcaino, 1992.. Eolian additions to soils will only influence weathering ratios if they contain cations being used in these calculations. Additions of eolian material, however, could influence the particle size of soils if dust deposition consistently occurs on a certain slope aspect. Since eolian additions to soils may be quite significant on cinder cones, especially on young cinder cones with high surface roughness, patterns of dust deposition may be important to soil development ŽMcFadden et al., 1986.. In order to assess the presence and any patterns of eolian additions to soils on the Springerville cinder cones, X-ray diffraction was used on all 10-cm bulk soil samples to identify eolian quartz and on a subset of 10-cm clay fractions to identify eolian mica. X-ray diffraction analyses of 10-cm soil samples revealed quartz in all cinder cone soils. Fig. 6A displays a representative X-ray diffraction pattern of a 10-cm soil sample

Fig. 6. X-ray diffraction patterns for two representative soils in the SVF. ŽA. X-ray diffraction patterns of a 10-cm bulk soil sample and a crushed cinder from 80 cm in pedon 3-S. ŽB. X-ray diffraction patterns from clay fractions for 10- and 80-cm samples from pedon 6-NE.

60

J.A. Rech et al.r Catena 43 (2001) 49–62

and unweathered cinders from the same profile. The majority of soil minerals, including magnetite, maghemite, hematite, pyroxene, and plagioclase, are from weathered cinders, while quartz in the 10-cm soil sample is eolian in origin. No trend of eolian quartz was found with aspect, and therefore dust deposition patterns do not appear to contribute to differences found in soil texture with aspect. X-ray diffraction data also reveals the addition of eolian mica to 10-cm soil samples, but not at depth ŽFig. 6B.. No pattern was found between slope aspect and concentration of eolian mica.

4. Discussion and conclusions This study found soils on south-facing slopes of cinder cones in the SVF to have deeper solums, finer textures, and lower Ca:Zr ratios, indicating greater chemical weathering, than soils on north-facing slopes. Soils on north-facing slopes have lower pH values, shallower solums, and coarser textures than soils on south-facing slopes. No trend was found between the deposition of eolian dust and slope aspect. Differences in soil development likely result from differences in the amount of insolation received by opposing slopes. Higher temperatures on south-facing slopes could increase rates of chemical weathering on these aspects. The relatively rapid rate of cinder cone weathering, due to the high concentration of unstable mafic minerals and large surface area of vesicular cinders, will also enable slight differences in weathering rates to be manifested in soil development. Other factors that could influence weathering rates include the number of freeze–thaw cycles and the availability of moisture on slopes. It is also possible, however, that differences in weathering and soil development are the result of differences in hillslope stability. Differences in vegetation caused by microclimatic differences could make south-facing slopes more stable and thereby cause soils on these slopes to become more developed. Cinder cones in SVF generally range in age between ; 1 and 2 Ma. Therefore, it is important to place weathering environments and vegetation communities on cinder cones within the context of a glacial climate since glacial conditions prevailed for the majority of the Pleistocene. A cooling on the order of 5–88C would have significantly influenced soil temperatures, snow cover, and vegetation communities on cinder cones. Springerville Ž2150 m. and McNary Ž2235 m., which are lower in elevation than most of the cinder cones in SVF, have average annual temperatures of ; 88C. Temperatures on cinder cones, especially on north-facing exposures, are lower than this due to the effects of elevation and slope aspect. During the last glacial, temperatures on north-facing exposures may have been - 08C. These low temperatures would have significantly reduced chemical weathering on these slopes, and may have caused permafrost conditions that effectively stopped chemical weathering on these slopes. At this time it is difficult to assess what role slope aspect has played in controlling slope stability, and ultimately cinder cone morphology in the SVF over time. Microclimatic differences resulting from slope aspect appears to influence rates of chemical weathering and thereby both solum thickness and soil texture. Further study is necessary to determine how these differences may influence permeability, overland flow, and general slope stability on these cinder cones.

J.A. Rech et al.r Catena 43 (2001) 49–62

61

Acknowledgements We wish to thank Pete Van de Water and Mary Kay O’Rourke of the NHEXAS project, Arizona Prevention Center, at the University of Arizona for use of the Spectrace 9000 XRF. Support was provided to Jason A. Rech by the NASA space-grant program. We would also like to thank Jay Quade for his helpful comments. This paper benefited from reviews by Peter W. Birkeland and an anonymous reviewer.

References Birkeland, P.W., 1999. Soils and Geomorphology, 3rd edn. Oxford University Press, Oxford, 430 pp. Carter, B.J., 1991. Slope gradient and aspect on soils developed from sandstone in Pennsylvania. Geoderma 49, 199–213. Condit, C.D., Crumpler, L.S., Aubele, J.C., 1989a. Patterns of volcanism along the along the southern margin of the Colorado Plateau: the Springerville field. J. Geophys. Res. 94, 7975–7986. Condit, C.D., Crumpler, L.S., Aubele, J.C., 1989b. Springerville volcanic field. In: Chapin, C.E., Zidek, J. ŽEds.., Field Excursions to Volcanic Terranes in the Western United States. Southern Rocky Mountains Region, vol. 1, New Mexico Bureau of mines and Mineral Resources, Memoir 46. Condit, C.D., Crumpler, L.S., Aubele, J.C., 1994. Thematic geologic maps of the Springerville volcanic field, east-central Arizona. US Geological Survey Miscellaneous Investigations Series Map I-2431. Cooper, A.W., 1960. An example of the role of microclimate in soil genesis. Soil Sci. 90, 109–120. Crumpler, L.S., Aubele, J.S., Condit, C.D., 1994. Volcanoes and neotectonic characteristics of the Springerville volcanic field, Arizona. New Mexico Society Guidebook. 45th Field Conference, Mogollon Slope, west-central New Mexico and east-central Arizona. Daniels, W.L., Everett, C.J., Zelazny, L.W., 1987a. Virgin hardwood forest soils of the Southern Appalachian Mountains: I. Soil morphology and geomorphology. Soil Sci. Soc. Am. J. 51, 722–729. Daniels, W.L., Everett, C.J., Zelazny, L.W., 1987b. Virgin hardwood forest soils of the Southern Appalachian Mountains: I. Weathering, mineralogy, and chemical properties. Soil Sci. Soc. Am. J. 51, 730–738. Davis, S.E., 1976. The influence of slope aspect on selected soil properties, Greens Peak, Apache County, Arizona. MS thesis, Dept. of Soil and Water Science. Dohrenwend, J.C., Wells, S.G., Turrin, B.D., 1986. Degradation of quaternary cinder cones in the Cima volcanic field, Mojave Desert, California. Geol. Soc. Am. Bull. 97, 421–427. Dymond, J., Biscaye, P.E., Rex, R.W., 1974. Eolian origin of mica in Hawaiin soils. Geol. Soc. Am. Bull. 85, 37–40. Fanzemier, D.P., Pederson, E.J., Longwell, T.L., Byrne, J.G., Losche, C.J., 1969. Properties of some soils in the Cumberland Plateau as related to slope, aspect, and position. Soil Sci. Soc. Am. Proc. 33, 755–761. Finney, H.R., Holowaychuk, N., Heddleson, M.R., 1962. The influence of microclimate on the morphology of certain soils of the Allegheny Plateau of Ohio. Soil Sci. Soc. Am. Proc. 33, 755–761. Gile, L.H., Hawley, J.W., Grossman, R.B., 1981. Soils and geomorphology in the Basin and Range area of southern New Mexico — Guidebook to the Desert Project. New Mexico Bureau of Mines and Mineral Resources Memoir 39, 222 pp. Graham, R.C., Franco-Vizcaino, E., 1992. Soils on igneous and metavolcanic racks in the Sonoran Desert of Baja California, Mexico. Geoderma 54, 1–21. Hooper, D.M., Sheridan, M.F., 1998. Computer-simulation models of scoria cone degradation. J. Volcanol. Geotherm. Res. 83, 241–267. Kearny, T.H., Peebles, R.H., 1951. Arizona Flora. University of California Press, Berkeley, CA, 1032 p. Klemmedson, J.O., 1964. Topofunction of soils and vegetation in a range landscape. Am. Soc. Agron. 5, 176–189, special publication. Losche, C.K., McCracken, R.J., Davey, C.B., 1970. Soils on steeply sloping landscapes in the Southern Appalachian Mountains. Soil Sci. Soc. Am. Proc. 34, 473–478. Machette, M.N., 1985. Calcic soils of the southwestern United States. Geol. Soc. Am., Spec. Pap. 203, 1–21.

62

J.A. Rech et al.r Catena 43 (2001) 49–62

Macyk, T.M., Pawluk, S., Lindsay, D., 1978. Relief and Microclimate as related to soil properties. Can. J. Soil Sci. 58, 421–438. McFadden, L.D., Wells, S.G., Dohrenwend, J.C., 1986. Influences of quaternary climatic changes on processes of soil development on desert loess deposits of the Cima volcanic field, California. Catena 13, 361–389. Porter, S.C., 1972. Distribution, morphology, and size frequency of cinder cones on Mauna Kea Volcano, Hawaii. Geol. Soc. Am. Bull. 83, 3607–3612. Reeves, R., 1996. Cinder cones and the valley asymmetry problem. Association of American Geographers Annual Meeting, Abstract Volume. Renault, C.E., 1989. Hillslope processes on late quaternary cinder cones of the Cima volcanic field, Eastern Mojave Desert, California. Masters thesis, University of New Mexico. Rex, R.W., Syers, J.K., Jackson, M.L., 1969. Eolian origin of quartz in soils of Hawaiian Islands and in Pacific pelagic sediments. Science 168, 277–279. Scott, D.H., Trask, N.J., 1971. Geology of the lunar crater volcanic field, Nye County, Nevada, Geological Survey Professional Paper 599-I. Sellers, W.D., Hill, R.H., 1974. Arizona Climate. University of Arizona Press, Tucson, AZ. Wood, C., 1980. Morphometric analysis of cinder cone degradation. J. Volcanol. Geotherm. Res. 8, 137–160.