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Home , Sedimentary structures, Ubehebe Crater

BRUCE M. CROWE \ Department of Geological Sciences, University of California, Santa Barbara, RICHARD V. FISHER j Santa Barbara, California 93106 Sedimentary Structures in Base-Surge Deposits with Special Reference to Cross-Bedding, Ubehebe Craters, Death , California

Note: This paper is dedicated to Aaron and Elizabeth more km2. The volcanic field is named from Waters on the occasion of Dr. Waters' retirement. the largest crater, Ubehebe. Following the recognition of base-surge depositions in the rim beds of Ubehebe Crater ABSTRACT (Fisher and Waters, 1969, 1970), the present Ubehebe craters, , California, study was undertaken to evaluate in greater include over a dozen volcanoes formed detail the physical characteristics of base-surge primarily by phreatic eruptions of trachybasalt deposits in order to gain possible insights into through a thick and permeable fanglomeratic flow mechanisms of base surges. Particular sequence on the north slope of Tin Mountain. attention is given here to the forms de- derived from Ubehebe Crater, the scribed as at Ubehebe by Fisher and largest crater in the area, is characteristically Waters (1970). thinly bedded or laminated and was deposited The Ubehebe craters originated on the by airfall and base-surge processes. Thick- gullied northern slope of Tin Mountain in late bedded deposits showing evidence of mass flow Pleistocene or Holocene time following the dis- occur where base surges were concentrated appearance of ancient Pleistocene (?) lake within, and followed which had been waters. About 4 km north of the craters, tuff carved into the fanglomerate prior to eruption. from Ubehebe rests on lake deposits exposed Cross-bedded sequences were deposited by in the valley floor. The ancient lake has been base surges that moved radially outward from named Lake Rogers and was present during Ubehebe Crater. They occur in the form of Pleistocene time (Clements, 1954). The vol- relatively small and large dunelike structures canoes exploded through, and their deposits with spacing and morphologic features similar rest upon, a fanglomeratic sequence at least 500 to antidunes and migration patterns somewhat m thick. similar to climbing ripples. The largest in the area are composite structures that preserve X a sequence of bed forms deposited in the high flow regime. apparently began in "N X'« \ \ the phase of the upper flow regime, \ Ubthibt progressing in time through sinuous lamination i to plane beds as flow power decreased. Lamina- t tions are well developed and bed forms are preserved at each level within the composite \ California structures because of a high rate of deposition Ubehebe and high cohesion during flow of the Craters base surges. V-, ^f ^ %\ INTRODUCTION £ Tin % 1 km IN \ J Mountain • ' The Ubehebe craters area, located in Death See it Valley, California (Fig. 1), includes 13, possibly 16, volcanic craters within an area of about Figure 1. Index map showing location of Ubehebe 3 km2. Ejecta from the craters covers 15 or craters area.

Geological Society of America Bulletin, v. 84, p. 663-682, 14 figs., February 1973 663

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The fanglomerate consists of thick-bedded to The largest crater, Ubehebe Crater, is a massive, highly lenticular beds of roughly circular tuff ring (terminology of and with clasts composed Fisher and Waters, 1970) 0.7 to 0.8 km in predominantly of volcanic and metamorphic diameter and 235 m deep. The diameter of the rock varieties with lesser amounts of sedimen- crater at the original eruptive surface (top of tary and plutonic fragments. The sandstone fanglomerate) is about 0.6 km. The shape of interbeds and matrix of the coarse-grained the crater is modified in the northwestern and layers are composed of lithic fragments and southeastern parts by preemption topography minerals derived from materials as diverse as and posteruption slumping. the large clasts. The rocks are poorly sorted, Ejecta from Ubehebe Crater attain a maxi- weakly cemented with , and highly mum thickness of 50 m at the crater rim. The permeable. deposits generally decrease in thickness radially The Ubehebe craters are here divided into from the crater and dip gently outward at 10° (1) Ubehebe Crater, (2) Little Hebe Crater, to 15° except for local thickening and draping (3) a western crater cluster, and (4) a southern within preexisting gullies carved into the crater cluster (Fig. 2). fanglomerate. At one place on the southeast

PROBABLE SEQUENCE OF ERUPTIVE EVENTS OF THE UBEHEBE CRATERS

Nonphreatic vulcanian eruptions developed cinder cone located near crater no. 1; final stages of activity Strombolian. Vent area of cinder cone may have coincided with vent area of crater no. 1.

Phreatic eruptions formed crater no. 1 and destroyed cinder cone. Crater no. 2 developed approxi- mately contemporaneously with crater no. 1—both are explosion craters with little rim ejecta. Cra- ter nos. 3 and 4 developed after crater no. 1 and prior to Ubehebe Crater. Phreatic explosions of Western Crater Cluster may have been contsmporaneous with activity from Slouthern Crater Cluster.

Mild volcanic activity from Little Hebe Cra:er developed small spatter cone which was disrupted by phreatic base-surge forming eruptions from same vent, greatly widening Little Hebe Crater.

Repeated, phreatic, base-surge forming eruptions formed Ubehebe Crater; ejecta from Ubehebe Crater covers all craters in volcanic field.

Figure 2. Index map showing crater designation and probable sequence of eruptive events.

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side of the rim, inward dipping strata are rim sequence include agglomerate (on the preserved. south side) derived from early cinder cone Inside the eastern portion of the crater below activity and a thin sequence of tuff identical the rim deposits are excellent exposures of the in kind to beds from Ubehebe which were basement fanglomerate. It is intensely fractured derived from earlier phreatic eruptions within and faulted, probably due to explosive crater the southern and western crater cluster groups. formation rather than tectonic processes. It is estimated that well over three-fourths of The western half of Ubehebe Crater has the 50-m rim-bed tuff sequence originated from been modified by posteruption slumping, which Ubehebe. is particularly pronounced on the northwest Beds derived from Ubehebe Crater contain side where slumped debris partially covers a accidental material derived from the under- resistant white lens of volcaniclastic sandstone lying fanglomerate, accessory ejecta from within the fanglomerate. Small debris flows pre-Ubehebe Crater vulcanian activity, and which develop from infrequent rains on poorly juvenile sideromelane fragments with some consolidated tuff are active on the inside slopes bombs derived from the Ubehebe eruption. It of the crater. The relatively flat floor oc- is likely that all three kinds of ejecta from the casionally contains ephemeral lakes. earlier eruptions were reincorporated with the Little Hebe Crater is a small cone with a early ejecta of Ubehebe. Color variations of the diameter of 100 m and a depth of 20 m. It is beds reflect the abundance of the various composed of agglutinated spatter overlain by a constituents: those rich in accidental debris 5- to 8-m veneer of pale red to orange base- are grayish-brown, those with abundant basaltic surge deposits derived from Little Hebe, and fragments are dark gray, and beds rich in is draped with gray tuff beds derived from sideromelane are light gray. Ubehebe Crater. Under the microscope, juvenile ejecta are The southern crater cluster consists of four hyalopilitic, although some samples are pilo- probable craters greatly modified by , taxitic due to microlite orientation during by the breaching of crater walls by adjacent aerial flight. Phenocrysts include kaersutite, craters (including Ubehebe), and by partial augite, and plagioclase. Plagioclase microlites covering with volcanic ejecta from Ubehebe are andesine to calcic-andesine; micropheno- Crater. Little Hebe Crater is nestled in the crysts and phenocrysts (calcic-oligoclase to northernmost crater (crater no. 1) of this andesine) are highly resorbed with cloudy cores cluster. filled with inclusions of glass, iron oxides, and The western crater cluster consists of seven rare clinopyroxene; thin sodic rims surrounding craters (including two craters somewhat south the cloudy cores are common. Kaersutite of the aligned crater cluster). The craters are occurs as scattered phenocrysts and micro- highly eroded and are draped with ejecta from phenocrysts but does not occur in the ground- Ubehebe Crater. Most are explosion craters mass. It is yellow-brown in plane light, has a with little rim ejecta, although the larger ones 2VX of about 67°, and is invariably surrounded appear to have sufficient ejecta surrounding by opacitic rims of magnetite and clino- their vents to be considered tuff rings. pyroxene. Clinopyroxene, occurring as pheno- Ejecta from Ubehebe Crater are most crysts, microphenocrysts, and microlites, has a voluminous and cover all preexisting craters; 2VZ of 44°, indicating that it is calcium-rich thus, Ubehebe was formed by the last and augite. Glomeroporphyritic clots, some ob- largest eruptive episode. Permeable served in hand specimens, are common. They within the underlying fanglomerate doubtless consist mainly of augite with lesser amounts of supplied water for the phreatic explosions. resorbed plagioclase and rare olivine. Ground- The probable eruptive sequence of Ubehebe mass glass is fresh, greenish-brown, and charged craters is given on Figure 2. with opaque iron oxides and plagioclase crystallites. Mineralogically, the juvenile ejecta are olivine-augite basalt. UBEHEBE CRATER AND ITS DEPOSITS Quickly chilled sideromelane shards are present in varying amounts (up to 15 percent Composition of the -size fragments) and were examined The rim deposits of Ubehebe Crater include in 38 grain mounts in the 2.5-^-size fraction. medium- to well-bedded tuff, lapilli tuff, and They have the characteristics of shards pro- tuff . The lowermost beds within the duced by phreatomagmatic eruptions described

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by Heiken (1972). The grains are blocky and graphic highs into lows within a very short have irregular-shaped surfaces due to brittle distance. On a small scale, beds pinch and swell fracturing. They are fresh and unaltered, and and coalesce and split when traced laterally, contain small plagioclase and clinopyroxene in contrast to the mantling and lateral con- crystals and disseminated iron oxides. Plagio- tinuity typical of airfall deposits. Although clase laths in the sideromelane grains are airfall deposits may slump or be washed into broken at grain margins, indicating growth of topographic lows following deposition, evi- plagioclase prior to explosive fragmentation. dence of reworking is usually present. Many of the larger sideromelane grains have 3. There is plastering of ejecta layers against tachylitic cores. Vesicles are relatively rare, topographic features at angles greater than the but when present they are generally confined to angle of repose, even vertical surfaces. The thin- the tachylitic cores. This suggests that bubble bedded, undisturbed layering of such deposits, growth was terminated by fragmentation. especially on vertical surfaces, requires deposi- Vesicles are invariably spherical, in marked tion from horizontally moving currents carry- contrast to stretched vesicles in the tachylite ing cohesive debris. Examples of plastering are observed in grain mounts studied from the shown in the photographs of Waters and Fisher early cinder deposits. Tachylite grains from (1971, Figs. 15, 16, 17). the cinder deposits are highly irregular in shape 4. There is thin, relatively continuous bed- with rough jagged edges due to breakage across ding of vent deposits. vesicles, and show fluidal shaping and a greater 5. Vesiculated tuffs may be present (Lorenz, vesicle abundance than the sideromelane grains. 1970). Recent work by Walke.r (1971) raises ad- General Sedimentary Features ditional possibilities of distinguishing airfall from deposits. He accumulated Introduction. Individual beds in the rim 1,300 mechanical analyses of airfall deposits and sequence of Ubehebe Crater are thin and over 300 mechanical analyses of pyroclastic continuous, a characteristic feature of maar flow deposits and plotted their values volcanoes (Waters and Fisher, 1970). Such beds versus median diameter. From this data he superficially look like tuff of airfall origin, but shows that fall and flow deposits cluster into transitional relationships of cross-bedded strata separate fields, although with some overlap with plane parallel bed forms make such an (Walker, 1971, Figs. 1, 2). origin for all of the beds suspect (Fisher and Size Analyses. Mechanical analyses of 51 Waters, 1969, 1970). Indeed, some beds which Ubehebe ejecta deposits were completed and appear to be plane parallel show internal low add to size data on base-surge deposits reported angle cross laminations on fresh exposures. by Fisher and Waters (1970) and Waters and Sedimentary structures at Ubehebe include Fisher (1971). One sample is of cross-bedded - or ripplelike bed forms, low angle cross base-surge deposits from Panuum Crater, a laminations, bedding sags, and a variety of small rhyolitic maar (with central plug dome) other "soft-sediment" structures. near Mono Lake, California. Most of the an- Airfall versus Emplacement by Flow. alyzed samples from Ubehebe craters are from Primary airfall deposits tend to mantle pre- deposits of known base-surge origin, although existing topographic irregularities, and they several are of airfall origin. Some samples are are never cross-bedded. Normal grading tends from plane beds whose origin is difficult to to develop in accordance with fall velocity of determine by field evidence. The size analyses particles. Base-surge deposits are generally are listed on Table 1. characterized by one or more of the following Median diameter (Mdv) ve rsus Inman sort- megascopic features: ing coefficient (o>) (Inman, 1952) for the 1. They exhibit low angle cross-bedding. samples are plotted on a graph showing This is particularly diagnostic if the cross- Walker's (1971) empirically derived airfall and bedding shows that flows moved radially out- pyroclastic fields (Fig. 3). Samples from cross- ward from the vent, or moved uphill. bedded base-surge sequences (Taal, Panuum 2. There is lenticularity of the deposits. On Crater, Ubehebe; see Fig. 3) are generally a large scale, the thickness of base-surge deposits better sorted than most of Walker's flow is initially controlled by the underlying topog- deposits and extend into the fall field. All of raphy. This is especially significant where the samples designated as probable base-surge individual beds thicken markedly from topo- deposits, one plane bed sample, and five samples

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TABLE 1. SIZE PARAMETERS OF UBEHEBE SAMPLES

Median Sorting Median Sorting Sample diameter* coefficient Sample diameter* coefficient no. <%> Comments no. (•V

A 1 1.80 1.44 Base surged foreset 24 2.2 1.35 Probable base surge (lee) of dune structure 25 -0.8 1.95 Maar sequence 2 0.87 1.31 Base surge; crest of dune structure 26 2.2 1.10 Maar sequence

3 1.28 1.40 Base surge; 27 -3.0 1.20 Maar sequence trough of dune structure 28 1.7 1.55 Maar sequence 4 1.63 1.48 Base surge; foreset of dune structure 29 -2.4 1.65 Maar sequence

5 1.08 1.14 Base surge; 30 -1.4 1.45 Maar sequence crest of dune structure 31 -1.9 1.60 Maar sequence 6 1.63 1.77 Base surge; trough of dune structure 32 0.9 1.90 Maar sequence

7 1.80 1.50 Base surge; foreset 33 2.1 1.10 Probable base surge of dune structure 34 1.6 1.05 Probable base surge S 1.11 1.10 Base surge; crest of dune structure 35 -1.9 2.20 Maar sequence

9 -0.80 1.70 Base surge; 36 1.8 0.65 Probable base surge plane bed beneath dune structure 37 -3.1 0.90 Maar sequence 10 0.31 1.68 Base surge; plane bed 38 -1.5 2.05 Maar sequence 11 2.27 1.25 Base surge; foreset of dune structure 39 -2.2 1.45 Airfall; black cinder layer 12 1.73 1.28 Base surge; backset (stoss) of dune structure 40 1.2 1.70 Maar sequence

13 1.82 1.44 Base surge; foreset 41 1.1 1.70 Maar sequence of dune structure 42 1.6 0.70 Maar sequence 14 1.82 1.35 Base surge; foreset of dune structure 43 0.4 1.90 Maar sequence

15 1.40 1.45 Base surge; backset 44 1.9 0.80 Probable base surge of dune structure 45 -1.7 1.45 Airfall; 16 0.10 1.40 Base surge; plane bed black cinder layer

17 1.67 1.80 Base surge; plane bed 46 1.7 1.05 Probable base surge

18 1.06 1.37 Base surge; 47 -2.7 0.80 Airfall; trough of dune structure black cinder layer

19 1.26 1.55 Base surge; 48 1.7 0.60 Probable base surge trough approaching crest 49 -0.8 0.95 Airfall; 20 1.06 1.37 Base surge; black cinder layer trough of dune structure 50 1.9 1.20 Probable base surge 21 -0.30 1.65 Base surge; plane bed 51 -1.1 1.45 Probable base surge 22 -3.1 1.95 Airfall; black cinder layer 52 3.2 1.03 Panuum Crater near Mono Lake; cross-bedded 23 -1.2 2.60 Maar sequence5 dune structure

'Median diameter and sorting coefficient in phi units: 4> 3 -log2 in millimeters; a^ = 16^-84^/2 (Inman, 1952). ^Base-surge deposits as designated in the field include cross-bedded structures and plane beds transitional with cross-bedded structures. §"Maar sequence" used if field characteristics of sampled beds did not allow distinction between base surge or alrfall. probable base surge" used if, in limited exposure, sampled bed vaguely cross-bedded or lenticular.

from the Ubehebe rim sequence plot within the samples are indistinguishable from airfall beds area which includes samples from the cross on the basis of size parameters, but tend to be beds. Except for one sample, however, all of the coarser grained than the cross-bedded layers. plane beds which are interpreted as base-surge It is not possible to distinguish the plane beds deposits because of their transitional relations of the rim sequence from airfall beds on the with cross beds, lenticularity, poor sorting, and basis of parameters; some plot in lack of grading lie outside the area encircling Walker's flow field but most correspond to air- samples from the cross beds. Thus, these fall deposits.

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-4 -3 -2 -I 0 12 3 4 Md ? Figure 3. Median diameter (Md^) and Inman (1952) base-surge deposits from Paiiuum Crater near Mono sorting (o^) plots of base-surge deposits superimposed Lake, California. Sorting coefficients reported from on Walker's (1971) flow and fallout fields. Dashed Waters and Fisher (1971, Table 1) for Taal sample lines, Walker's flow field; solid lines, fallout field. numbers 11, 14, and 18 inadvertently recorded as Contour lines designated with "8" enclose greatest Inclusive Graphic Standard Deviation of Folk (1965) density of Walker's samples. Dotted line encloses rather than Inman (1952) sorting coefficient (o^). cross-bedded Ubehebe base-surge deposits (including Corrected sorting coefficient values (

Flow Direction Measurements. Flow dire c- impact, probably due to the presence of inter- tions, measured from cross beds, are plotted stitial water. along with the directions of ballistic trajectories Contorted Stratification. Contorted strati- of blocks as determined from the geometry of fication (excluding bedding sags) occurs at bedding sags produced by impact (Fig. 4). several localities in thick, fine-grained beds All flow directions were measured from max- deposited within but not outside preexisting imum cross-bedding inclinations by dissecting channels. The term "con:orted stratification" the poorly consolidated tuff with a shovel. is used as a descriptive term for all disturbed With few exceptions, flow direction measure- stratification regardless of origin (Dott and ments show that currents moved outward from Howard, 1962). Ubehebe Crater. Flow directions measured The most common structure is disturbed within tuff beds deposited in preexisting bedding; that is, beds which were disturbed channels, however, show that the flows were after deposition and prior to consolidation or diverted by the channels and moved parallel to tectonic deformation (Crowell and others, the walls. On divides between the 1966). One spectacular occurrence consists of channels, flow directions trend radially away tightly folded overturned anticlines and syn- from Ubehebe Crater. clines, generally witli one limb thinned due to Bedding Sags. In addition to showing tra- shearing (Fig. 5). The folds occur in fine- jectory directions, a significant feature of grained ( to fine sand) massive beds with bedding sags is the induced plastic deformation interbedded, probable airfall cinder layers and flow of the impacted beds. This indicates which are intimately involved in the folding. that the beds were cohesive at the time of Tilt of the folds is variable and generally is

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elongation of some of the disturbed bedding features. The massive beds within the channels are notably finer grained and are generally more poorly sorted than beds outside the channels. The differences discussed above are shown within individual layers which can be traced across channels and onto divides between channels. Differences between beds within and outside of the channels probably result from variations in particle concentration within different parts of a flow and the confining or funneling effects of the channel through which the flows moved. Because particle concentration is likely to be greatest near the basal part of a moving base surge (Fisher and Waters, 1970), probably similar to the basal portions of nuées ardentes (Smith, 1960), or analogous to the bedload of a Figure 4. Map showing bedding sag trajectory swiftly moving , the greatest volume of directions and directions measured from cross highly concentrated debris was confined and beds in tuff from Ubehebe Crater. moved within the channels, whereas less con- unrelated to the demonstrable flow direction centrated and unconfined material swept over or local paleoslopes. There are no associated the channel sides and led to the deposition of cross beds or pinching and swelling of lamina- markedly different beds within a short distance tions characteristic of convolute laminations. across the axes of the channels. An increase in At some locations, thin tuff layers associated particle concentration results in a decrease in with thick, massive beds have been pulled apart the sorting ability of a flow as well as rapid (Fig. 6). Portions of the disrupted layers are deposition once deposition begins. Aligned curled and appear to lie disconnected within the fragments in some of the massive beds (Fig. 9) massive tuff. suggest that emplacement may have been by laminar flow (Fisher, 1971). Thus, the con- Some of the contorted stratification shows fined portion of the flow tended to produce evidence of the influence of currents on their rapidly deposited, poorly sorted beds which origin. A few flame structures, for example, are were highly unstable and easily distorted after present which are elongate in the flow direc- deposition. tion (Fig. 7). Also, in places, some of the folds of the disturbed bedding are elongate and Heiken (1971) attributes the origin of overturned in the flow direction. disturbed bedding in tuff rings of south- Channeled versus Unconfined Base Surges. central Oregon to gravity slumping, perhaps There is considerable contrast between the induced by disturbances due to eruptive events. base-surge deposits that occur within the pre- The disturbed bedding of the Ubehebe craters existing channels and those outside the channels is probably due to combinations of current- (Fig. 8C). On divides between channels, and induced deformation and gravity slumping where base surges moved unconfined across perhaps triggered by seismic events associated relatively level ground, the deposits are with volcanic eruptions. Pull-aparts suggest medium- to thin-bedded, laterally continuous, that the massive fine-grained beds moved and commonly cross-bedded. Within the pre- plastically for short distances by slow creep existing channels, however, many beds tend to after deposition. be thick and massive ; cross-bedding is relatively rare, and contorted stratification is common. CROSS-BEDDED STRUCTURES Flow directions shown by cross-bedded layers within the channels sloping down from Tin Introduction Mountain are invariably parallel to the channel Inclined laminations at Ubehebe craters walls and show that the flows moved uphill occur within single beds which have planar within the channels. Similar flow directions are upper and lower surfaces or within dune- and shown by elongation directions of flame struc- ripplelike structures which have undulating tures and by directions of overturning and upper surfaces and planar to gently curved

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Figure 5. Contorted stratification in relatively thick direction of photograph and parallel to exposure, beds within a filled preexisting . Axis of gully in

lower boundaries. The undulatory structures, crests consistently migrate downcurrent, and although smaller, are similar to structures laminae tend to steepen. This steepening is developed by base-surge flows at Taal Volcano usually accomplished ay an upward increase (Moore, 1967; Waiers'and Fisher, 1971). in the angle of climb, although the angle may The largest dunelike structures within the be variable within single dune structures. The area are well exposed in a roadcut along the set of laminae on the stoss side tends to be paved road leading to Ubehebe Crater (Fig. thinner and finer grained than the lee-side set. 10). At this locality, single dune structures Therefore, erosion of the stoss side must have begin development on plane parallel surfaces occurred during migration and only the finer with a slight heaping up of debris with low grained and the most cohesive ash collected on angle lee-side laminae and without stoss-side that side. The lee-sid: set includes coarse- laminae. These small ripplelike features are grained tuff and lap.lli tuff units which followed by distinctly finer grained tuff show- alternate with fine-grained laminae similar in ing nearly symmetrical low angle lee-side and grain size to laminae on the stoss side; the fine- stoss-side laminae. The crests in successive grained layers are commonly continuous from laminae usually migrate downcurrent, although stoss side to lee side. Apparently the coarser in some dune structures one or two of the lower ash was less cohesive than the fine ash and was laminae show upcurrent crestal migration. As more easily swept frorr.. the stoss-side surface the structure builds up, however, the successive onto the lee side and there was preserved (Fig.

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Figure 6. Bed in upper center portion of photo- due to short distance mass movement of bed downhill graph shows thin, discontinuous layer of tuff near its (to right) following deposition. Note bedding sags top which has been pulled apart and curled, probably near base of exposure.

10). Migration and upward building of the however, the coarse-grained tuff shows poorly dunes terminates with a thin, fine-grained, developed and extremely low angle cross- finely laminated bed continuous across several bedding (Fig. 10). of the dunes, and is overlain by distinctly As shown on Table 2 and plotted on Figure coarser grained tuff which fills the troughs and 11 with similar data from other places, wave becomes plane parallel upward. Internally, lengths of the dunes range from 30 to 210 cm

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Figure 7. Flame structures sheared in rection of current. Pencil, 17 cm long. and wave heights range from 2.5 to 23.8 cm. Dune- or ripplelike structures that are Wave heights are taken as the distance between smaller than the structures exposed along the the crest and the base where build-up of :he paved road occur within tuff derived from structure begins, rather than heights taken from Ubehebe and exposed in gullies which dissect individual laminations because individual the ejecta aprons surrounding the craters. laminae usually cannot be traced from crest to Some of the most: continuous wave trains are trough. These data indicate that wave height exposed within gullies southeast of Little Hebe to length ratios increase rather systematica.y. Crater and between 0.7 and 1.0 km from the Changes in size of the undulations are doubt ess center of Ubehebe Crater. In this area the base related to the strength of the flows as deter- surges traveled uphill within the gullies; sub- mined by the explosive strength of the erup- sequent erosion parallel to the current direction tion and the angle of the slope over which the provides excellent expasures. As shown on flows move. Table 3, wave lengths range from 65 to 155 cm These structures were termed "antidunes" and wave heights from 3 to 8 cm. These data, by Fisher and Waters (1970) because of the plotted on Figure 11, are consistent with regular sinuosity of their upper surfaces, similar data from the larger dunelike structures abundant preservation of stoss-side laminae, discussed previously, with wave height tending lee-side laminations with dip angles less than to increase with wave length. This relationship the angle of repose, and some evidence of up- appears ;o also held true for the dunes formed current migration of internal crestal axes at Taal Volcano, Philippines (Waters and within individual dunes (Fisher and Waters, Fisher, 1971, Table 1). which are compared 1970, PI. 3). with the smaller Ubehebe structures on Figure

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/84/2/663/3429009/i0016-7606-84-2-663.pdf by guest on 27 September 2021 Figure 8. View downslope toward west showing center of gully. Base surges moved uphill in gullies preexisting gully carved in fanglomerate which con- toward observer. tains deposits of Ubehebe tuff. Tuff beds thicken in

Figure 9. Massive bed with crude internal stratifi- Upper few centimeters of bed become finer grained cation suggesting emplacement by laminar flow. Pebble- and develop laminations showing tendency to form size fragments in pebble trains show increase in size undulating upper surface; this may have been de- upward from base (inverse grading), indicative of posited by less dense "tail" of current passing over- mass flow (Fisher, 1971). Corroborating evidence of head which moved toward right. Scale, in centimeters. emplacement by flow is rapid lateral thickness change.

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Figure 10. Close-up of a dune exposed along paved (east to west), away from Ubehebe Crater. Sharpest road to Ubehebe Crater. Dune built up from planar crestal angle occurs at top of bedding set; mantled by surface. Lower part broad-crested with very low angle thin, continuous, internally cross-laminated bed. This stoss- and lee-side dips. Stoss- and lee-side laminae is followed by a distinctly though crudely bedded tend to become steeper higher in sequence. Coarsest lapilli tuff sequence becoming plane parallel which laminae occur on lee side. Migration from left to right reveals poorly developed low angle cross-bedding.

11. Because the largest of the Taal dunes small dunes for which depositional slope is formed at distances comparable to the Ubehebe not compensated (Fig. 13A) show that most structures (within about 1 km from the source), of the stoss-side dips ar~ greater than the lee- we suspect that the base surges at Ubehebe side dips. The reverse is true if slope is cal- were less powerful than those at Taal. culated at 0° (Fig. 13B). In general, these Although the gradients are relatively plots suggest that stoss-side slopes increase as constant within any one segment, individual lee-side slopes decrease, and vice versa, but the beds or laminae on which the small dunes are scatter cf points is wide. In one instance, lee- built are somewhat undulatory. The slope side laminae which developed on an uphill angles of the depositional surfaces underlying slope of 20° dip 13° downhill (Fig. 14). the dunes therefore vary within a few degrees The size, shape, and spacing of the small but commonly dip downstream (Table 3), dunelike structures are similar to the lower although they may be horizontal or dip up- parts of the large dunes, suggesting that they stream. Plots of wave length to wave height may have formed under similar hydrodynamic ratios versus the angle of depositional surfaces conditions of flow. The possibility that they on which the structures are built (Fig. 12) may be antidunes requires a brief review of the show that wave length tends to increase with subject. respect to height as the uphill depositional slope increases. The exact cause for this relation- Antidunes ship is obscure, but it is certain that minor Antidunes are transitory bed waves which changes in slope have an effect on energy con- form on beds of cohesionless sediment in the ditions of the flow and hence on the resulting upper flow regime of flowing water. They in- form of the waves; we do not know if the same clude all sinuous bed forms which are in phase relationship holds for structures formed from with steeper gravity surface waves, and they base-surge flows that moved downhill. may migrate upstream, downstream, or remain Plots of stoss-side versus lee-side dips of the stationary. The characteristics of antidunes are

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• ' » • • • • 1 TABLE 3. MEASUREMENTS ON SMALL DUNELIKE STRUCTURES BETWEEN ABOUT 0.8 AND 1.0 km FROM CENTER OF UBEHEBE CRATER

- (degrees ) lengt h

heigh t o zc (cm ) (cm ) •T-

•M angl e angl e Wav e (degrees ) slop e Wav e o; 2 Angl e depositiona l (degrees ) Lee-sid e Stoss-sid e e 1 1 o e o 110 5 22.0 -8* -14 +4 (+12) • % " • (-6)+ U2l t. _J • • o 110 6 18.2 -8 -10 (-2) +9 (+17) u 100 140 7 20.0 -8 -8 (0) +11 (+19) LEGEND .. .

0 Dunn «apoood along poind road itt . f 130 7 18.5 -7 -13 (-6) +3 (+10)

1 bm htm mitccllOMOu« oioai (tab ~ ? L • DunM in gull«,« SC of Ubahob* C 1 • • Ovnn al Too Volcano, niilippn«« 130 7 18.5 -7 -10 (-3) +4 (+11) I 1 . . ! a (Wat*t and Fith«(, I9TI, la " 70 5 14.0 -5 -14 (-9) +5 (+10)

75 5 15.0 -3 -13 (-10) +7 (+10)

65 4 16.3 -5 -11 (-6) +7 (+12) . . 1 . . . . . 1 . . . . 5 10 50 100 200 55 6 9.2 -1 -10 (-9) +12 (+13) WAVE HEIGHT (CM) Figure 11. Log-log plot of wave length and wave 60 5 12.0 0 -4 (-4) +12 (+12) height of dunelike structures measured at Ubehebe 60 6 10.0 0 -14 (-14) +9 (+9) and of four examples from Taal Volcano, Philippines. 70 4 17.5 -5 -7 (-2) +9 (+14)

85 5 17.0 -5 -8 (-3) +10 (+15) TABLE 2. WAVE LENGTH AND HEIGHT MEASUREMENTS OF UBEHEBE 6 -20 -13 (+7) DUNES FROM PAVED ROAD LOCALITY AND FROM GULLEYS ON UBEHEBE SLOPES - 6 - +6 -12 (-18) +9 (+3)

Wave Wave (-16) +4 Ratio 105 8 13.1 -7 -23 (+11) length height Comments WL/WH (cm) (cm) 130 8 16.3 -7 -22 (-15) +1 (+8)

180 15 12.0 Measured along 105 8 13.1 -7 -15 (-8) +7 (+14) paved road about 180 20 9.0 0.8 km northwest 155 8 19.4 -4 -12 (-8) +3 (+7) from center of 120 10 12.0 Ubehebe Crater 110 7 15.7 -4 -10 (-6) +2 (+6)

110 13.8 8.7 65 6 10.8 -2 -10 (-8) +3 (+5) 180 20 9.0 *- sign, downstream dip; + sign, upstream dip. In all 110 7.5 14.7 cases, transport direction upstream. ^Parentheses enclose angle values assuming a horizontal 180 15 12.0 surface of transport.

120 10 12.0 described by Gilbert (1914), Langbein (1942), 180 12.5 14.4 Simons and Richardson (1961, 1962), Simons 150 12.3 12.2 and others (1965), and Kennedy (1961, 1963, 120 10 12.0 1966).

140 12.5 11.2 As pointed out by Hand and others (1972), the stationary waves accompanying antidunes 150 12.3 12.2 produced by density currents do not occur at 150 21.3 7.4 the free-water surface, but instead may form 210 23.8 8.8 at a density interface within the fluid, as sug- gested by Waters and Fisher (1971, p. 5611) for 33 3.2 10.3 Measurements from gulleys surrounding base-surge flows. 30 3.5 8.6 Ubehebe Crater Based upon Kennedy's (1961) formula which 37 4.3 8.6 relates the wave length of antidunes in open 82 6.3 13.0 channel flow to current velocity, and assuming

54 5.2 10.4 that the mobility of the bed causes it to behave as a continuation, at depth, of the wave at the 150 15.5 9.7 density interface, Hand and others (1972) show 47 2.4 19.6 that the formula relating velocity of the density

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1971). Surface profiles are trochoidal (Hand, 1969) with broad troughs and smoothly rounded but relatively more sharply peaked crests. Internal stratification is commonly poorly develo|>ed and may dip either upstream or downstream at angles less than the angle of repose. Cross-stratification dipping upcurrent is particularly diagnostic, and was used by Power (1961) to suggest that coarse-grained sand in the Pleistocene Coso Formation (California) was deposited as antidunes, al- though the structures may represent deposition _J from chute and pool flow. Upstream-dipping laminae have been developed in the laboratory from high flow regime chute and pool flow by Jopling and Richardson (1966). Several problems are involved in classifying the Uoehebe dunes a,; antidunes. Perhaps the most serious objection is that the crests migrate downstream rather than upstream (Fig. 10). However, antidunes are capable of migrating downcurrent as well as remaining stationary. In addition to migration direction, crests of the Ubehebe dunes tenc to be sharper than trochoids. Examination of the shapes of in- dividual laminae from bottom to top of the large individual Ubehebe dunes, however, shows that wave heights are low and crests are broad near the base and only become sharper ANGLE OF DEPOSITIONAL higher in the sequence. This upward change in crestal shapes suggests that conditions of flow SLOPE changed as deposition progressed. It is also Figure 12. Plot of the ratio wave length-wave height versus angle of depositional slope for small possible that the changing geometry of the dunelike structures southeast of Ubehebe Crater. Data underlying surface may have influenced the from Table 3. shape of the next succeeding lamination, and so on through the sequence. The well-developed current, U, to antidune wave length, L, is laminations may be related to the cohesiveness U2 = [gL/{2tt)] [Ap/(2p + Ap)], of the debris at the time of deposition. Faint laminations developed during antidune flow in where p is the density of the fluid above the the laboratory (Middleton, 1965) resulted from interface, g is the acceleration due to gravity, deposition of cohesionless sand. and Ap is the difference in density between the fluid above the interface and that below The Ubehebe dunes also bear some similar- it. Further, they point out that inasmuch as ities to ripple-drift cross-lamination (Walker, antidunes cannot form when the denisometric 1963; McKee, 1965; Jopling and Walker, 1968; Froude number is much less than unity, the Allen, 1970a). As with ripple-drift, the Ubehebe minimum current velocity compatible with dunes show a migration of successive wave antidunes can be estimated forms up the stoss side of preceding wave forms, downcurrent crest migration, varying degrees U\ gD (Ap/p), in thickness of the stoss-side set of laminations, where D represents the thickness of the density and an upward increase in climb angle. current. Furthermore, the predicated appearance of The internal structures and profiles of de- ripple-drift types in unsteady flow (Allen, posits formed from antidune activity have beta 1970a, p. 21) is similar to the upward sequence described from studies (Middleton, of cross-lamination observed in the large 1965) and have been recognized in the ancier.t Ubehebe dune structures. rock record (Hand and others, 1969; Skipper, There are, however, some important dif-

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ANGLE OF LEE-SIDE ANGLE OF LEE-SIDE LAMINAE LAMINAE Figure 13. Angle of stoss-side laminae plotted correction for depositional slope. Lines sloping toward against angle of lee-side laminae for small dunelike left on diagrams A and B are where stoss-side dips structures southeast of Ubehebe Crater. A, Plot with- equal lee-side dips; other lines bound areas of plotted out correction for depositional slope; B, plot with points.

Figure 14. Photograph showing laminae developed surface. Base surge moved uphill from left to right, in lee of flow dipping 13° downhill on 20° depositional Lower border of photograph horizontal.

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ferences between the Ubehebe bed forms and erosional surface which may be overlain by ripple-drift cross-lamination. The Ubehebe another cross-bedded or plane parallel set of bed forms, for example, have much larger wave laminae (Fisher and Waters, 1969, Fig. 3; lengths and wave heights than typical ripple- Fisher and Waters, 1970, Figs. 5, 6; Waters drift cross-lamination. They also differ in that and Fisher, 1971, Figs. 24, 25). It therefore ripple-drift cross-laminations are characterized appears that the described large Ubehebe by superimposed ripple sets, whereas the dunes record the passage of a single base surge, Ubehebe dunes generally show only single sets whereas more typically there are successive with migrating crests and regular wave length base surges, each of which forms a bedding set spacing: climbing "dune structures" with and modifies underlying structures. superimposed "dune sets," however, have been Does the described sequence of bed forms observed in maar deposits by one of us (R.V.F.) within a single dune structure represent near Koko Crater, Hawaii, and near Macdoel deposition solely in the upper flow regime, a in northern California (Fisher and Waters, progression from upper flow regime to lower 1969, Fig. 3). Ubehebe dunes also differ from flow regime, or deposition solely in the lower ripple-drift cross-lamination in that the length flow regime? Little is known about the of the stoss side as measured along a horizontal mechanics of base-surge flow and deposition, line is commonly equal to or longer than the but using the concepts developed for flow in length of the lee side, and the angle of stoss- alluvial channels, the observed high velocities side laminae may be steeper than that of the (Moore, 1967) make: it especially appealing to lee-side laminae (see Walker, 1969, for discus- attribute the bed forms to deposition in the sion of ripple-drift geometry). upper flow regime. Two important variables in the development DISCUSSION of bed forms are flow power and grain size, with Cross-bedding observed in the rim beds at both factors decreasing through time during Taal Volcano in the Philippines (Moore, 1967; deposition from density currents. Allen (1970b) Waters and Fisher, 1971), Zuni Salt Lake in has discussed the importance of these factors New Mexico, and Salt Lake Craters in Hawaii on the sequential development of bed forms in (Fisher and Waters, 1970), and in at turbidity currents. The presently accepted bed Fort Rock-Christmas Valley in Oregon form sequence and bed form descriptions, how- (Heiken, 1971) exhibit characteristics similar to ever, have been derived primarily from flume the Ubehebe dunes. That is, within a single experiments under squilibrium conditions in bedding set, the lower laminae tend to have which the equilibrium bed form, flow depth, broad crests with very low angle stoss- end lee- flow velocity, and bed shear stress were all side laminae. Upward within a bedding set, dependent upon a specified fluid and crests become sharper and steeper and migrate constant grain size. However, because of the in the downcurrent direction. pulsating nature of phreatic eruptions (Miiller Observational and photographic studies of and Veyl, 1957) and the complexities of base surges (Moore, 1967; Waters and Fisher, formation of base surges (Waters and Fisher, 1971) indicate that energy loss during flow 1971), there may be considerable and rapid is rapid and that the base-surge flows rapidly changes in flow power, grain sizes, and sorting decelerate. Deposition at a point in space parameters within successive surges or even should reflect these deceleration effects through within individual surges. time or upward in sequence. Thus it is con- Other factors not studied in which cluded that single base-surge bedding sets greatly affect bed form geometry include reflect a sequential upward change in flow con- variations in the re.tio of suspension fallout ditions and are composite structures. Similarly, and traction movement. Generally, the de- changing flow conditions appear to be recorded creasing values of flow power in a decelerating in ripple-drift cosets (Walker, 1969). current should cause the ratio to rise markedly, The large Ubehebe dunes are especially particularly if the depositing debris is cohesive. significant, because at the described roadcut These factors have been considered for lower locality the bed forms are preserved in. their flow regime tied forms (Jopling and Walker, entirety. More commonly, as seen in other 1968; Allen, 1970b) but not for upper flow maar volcanoes and in places at Ubehebe, the regime bed forms. Furthermore, flume studies crestal portions have been destroyed and are of bed form development and bed form geom- immediately followed by a planar or undulating etry have generally been conducted under

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conditions of nondeposition. Aggrading condi- concentration also would decrease the bed tions are required for sedimentary structures shear stress required for antidune development. to be preserved without modification in the The basal zones of base-surge flows (and tur- . bidity currents) are doubtless highly charged Important considerations bearing upon the with particles and, during deceleration and problem of formation of sinuous structures and shortly before deposition, the concentration antidunes are the observations of fopling and should quickly rise and cause a rapid increase Walker (1968) and Skipper (1971). Jopling in the density and viscosity of the dispersion and Walker (1968), for example, describe a (Fisher, 1971), thereby decreasing the settling sequence of lacustrine beds which velocity of individual particles. Thus, because includes ripple-drift cross-lamination. The of concentration effects, the rate of decrease sequence displays sinuous (trochoidal ?) ripple in flow regime may be slowed and not reach laminations consisting of superimposed un- the lower flow regime dune or ripple stage dulating forms which have broad crests and before deposition is complete. troughs with low angle laminae continuous The differences in bed forms produced from stoss to lee sides. Where asymmetry in- within the channeled (thick and massive) creases and crests migrate downcurrent, sets and unchanneled (thin and cross-bedded) base- of stoss-side laminae become thinner than on surge deposits at Ubehebe further suggest the lee side and the ripples pass to "type B that if concentration values, and possibly ripples" (Jopling and Walker, 1968) where lee- depositional rates, become extremely high, the side dips tend to be somewhat greater than on production of normal high flow regime bed the stoss side. The upper surface of continuous forms is inhibited and massive deposits are laminae tend to form undulations somewhat formed similar, perhaps, to the "quick" bed similar in shape to the sinuous beds, but up- formed during deposition of experimental ward successions show crestal migration in one high concentration turbidity currents (Middle- direction. ton, 1967). Skipper (1971) illustrates a vertical sequence We suggest that the Ubehebe dunes and in a turbidite deposit where antidune cross- similar structures observed in the rim sequences stratification is closely followed by low angle of maar volcanoes elsewhere preserve a sinuous lamination grading up to ripple-drift sequence of high flow regime bed forms at cross-laminations, although his other sections different levels within the bedding set and that showing antidunes lack ripple-drift cross- each level was preserved because of the ex- lamination. At each locality, however, antidune tremely high rate of burial and high sediment cross-stratification occurs below a sinuous cohesion. Based upon comparable bed forms boundary with wave lengths varying from 40 produced in alluvial channels, the base-surge to 80 cm and amplitudes from 2 to 5 cm. The flows at Ubehebe apparently began deposition asymmetry of the sinuous boundary is identical in the antidune phase of the upper flow regime, to the trochoidal profiles characteristic of some progressing through time and upward in antidunes described by Hand (1969), where the sequence through sinuous laminations to plane steeper slope faces upstream. Spacing of ripple bed as flow power decreased. Changes in bed crests with the ripple-drift sequence is ap- form geometry upward in sequence were proximately equal to the underlying antidune influenced not only by decreasing flow power, crests, indicating that the ripples did not but also by changing fall velocities caused by develop in equilibrium with the prevailing rapid and increasing concentration values, by flow conditions at the time of their formation increasing ratio of suspension fallout to traction (Skipper, 1971). movement as the velocity decreased, and Fall velocity is the primary variable that possibly by the shape of the undulating determines the interaction between the bed cohesive surfaces beneath the bed forms as they material and the fluid (Simons and others, built upward. 1965). Inasmuch as fall velocity of particles is influenced by the density and viscosity of a ACKNOWLEDGMENTS fluid, an increase in either (or both) has the This study of Ubehebe craters, part of effect of reducing the fall velocity of particles, an investigation of maar volcanoes in the and therefore of effectively increasing the western United States, Mexico, Hawaii, New flow regime (Simons and others, 1965). A Zealand, and Europe, was financed by the decrease in fall velocity with rising particle National Aeronautics and Space Administra-

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tion (NASA NGL-05-010-019). Aaron Wa';ers, Inman, D. L., 1952, Measures for describing the co-investigator on this grant, was not directly size distribution of : Jour. Sed. involved with the field work at Ubehsbe, Petrology, v. 22, p. 125-145. although he was aware of the study anc closely Joplhg, A. V., and R chardson, E. V., 1966, Back- followed its progress, giving valuable assistance, set bedding developed in shooting flow in advice, and moral support. We prepared this laboratory experiments: Jour. Sed. Petrology, v. 36, p. 821-825. manuscript without his knowledge to appear Jopling, A. V., and Walker, R. G., 1968, Morphol- in this edition of the Bulletin in honor of (and ogy and origin of ripple-drift cross-lamination, to surprise) Aaron Waters. with examples fiom the Pleistocene of Mas- sachusetts: Jour. Sed. Petrology, v. 38, p. 971-984. REFERENCES CITED Kennedy, J. F., 1S'61, Stationary waves and Allen, J.R.L., 1970a, A quantitative model of antidunes in alluvial channels: California Inst. climbing ripples and their cross-laminated Technology, W. M. Keck Lab. Hydraulics deposits: , v. 14, p. 5-26. and Water Resources, Rept. KH-R-2, 146 p. 1970b, The sequence of sedimentary structures 1963, The mechanics of dunes and anti-dunes in , with special reference to dunes: in erodible bed channels: Jour. Fluid Me- Scottish Jour. Geology, v. 6, p. 146-161. chanics, v. 30, p. 741-773. Clements, Thomas, 1954, Geological story of 1966, Nomenclature for bed forms in alluvial Death Valley: San Bernardino, Calif., Inland channels: Am. Soc. Civil Engineers. Proc., Printing and Engraving Co., 62 p. Jour. Hydraulics Div., v. 92, no. HY3, p. 51- Crowell, J. C., Hope, R. A., Kahle, J. E., Oven- 64. shine, A. T., and Sams, R. H., 1966, Deep- Langbein, W. B., 1942, Hydraulic criteria for sand water sedimentary structures, Pliocene Pico waves: Am. Geophys. Union Trans., v. 23, Formation, Santa Paula Creek, Ventura Basin, p. 615-621. California: California Div. Mines and Geol. Lorenz, Volker, 1970, Some aspects of the eruption Spec. Rept. 89, 40 p. mechanism of the Big Hole maar, central Dott, R. H., Jr., and Howard, J. K., 1962, Con- Oregon: Geol. Soc. America Bull., v. 81, p. volute lamination in non-graded sequences: 1823-1830. Jour. Geology, v. 70, p. 114-120. McKee, E. D., 1965, Experiments on ripple Fisher, R. V., 1971, Features of coarse-grained, lamination, in Middleton, G. V., ed., Primary high-concentration fluids and their deposits: sedimentary structures and their hydro- Jour. Sed. Petrology, v. 41, p. 916-927. ciynamic interpretation: Soc. Econ. Paleontol- Fisher, R. V., and Waters, A. C., 1969, Bed forms in ogists and Mineralogists Spec. Pub. 12, p. base-surge deposits: Lunar implicaticns: Sci- 66-83. ence, v. 165, p. 1349-1352. Middleton, G. V., IS65, Antidune cross-bedding 1970, Base surge bed forms in maar volcanoes: in a large flume: Jour. Sed. Petrology, v. 35, Am. Jour. Sci., v. 268, p. 157-180. p. 922-927. Folk, R. L., 1965, Petrology of sedimentary rocks: 1967, Experiments on density and turbidity Austin, Tex., Hemphill's, 159 p. currents, i?t. III. Deposition of sediment: Gilbert, G. K., 1914, The transportation of debris Canadian Jour. Earth Sci., v. 4, p. 475-505. by running water: U.S. Geol. Survey Prof. Moore, J. G., 1967, Ease surge in recent volcanic Paper 86, 263 p. eruptions: Bull. Vulcanol., v. 30, p. 337-363. Hand, B. M., 1969, Antidunes as trochoidal waves: Müller, G., and Veyl, G., 1957, The birth of Jour. Sed. Petrology, v. 39, p. 1302-1309. Nilahue, a new rr.aar type volcano at Rinina- Hand, B. M., Wessell, J. M., and Hayes, M. O., hue, Chile:: Cenozoic volcanism: Internat. 1969, Antidunes in the Mount Toby Con- Geol. Cong., 20th, Mexico City 1956, sec. 1, glomerate (Triassic), Massachusetts: Jour. pt. 2, p. 375-396. Sed. Petrology, v. 39, p. 1310-1316. Power, W. R., Jr., 1961, Backset beds in the Coso Hand, B. M., Middleton, G. V., and Skipper, Formation, Inyo County, California: Jour. Keith, 1972, Antidune cross-stratification in a Sed. Petrology, v. 31, p. 603-607. turbidite sequence, Cloridorme Formation, Simons, D. B., and Richardson, E. V., 1961, Forms Gaspe, Quebec: Sedimentology, v. 18, p. 135— of bed roughness ii alluvial channels: Am. Soc. 138. Civil Engineers Proc., Jour. Hydraulics Div., Heiken, G. H., 1971, Tuff rings: Examples from v. 7, no. HY3, p. 37-105. the Fort Rock-Christmas Lake Valley basin, 1962, Discussion of bed roughness in alluvial South-central Oregon: Jour. Gcophys. channels: Am. Soc. Civil Engineers Proc., Research, v. 76, p. 5615-5626. Jour. Hydraulics Div., v. 88, no. HY4, p. 1972, Morphology and petrography of vol- 237-243. canic ashes: Geol. Soc. America Bull., v. 83, Simons, D. B., Richardson, E. V., and Nordin, C. p. 1961-1988. F., 1965, Sedimentary structures generated by

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flow in alluvial channels, in Middleton, G. V., 1969, Geometrical analysis of ripple-drift cross- Primary sedimentary structures and their lamination: Canadian Jour. Earth Sci., v. 6, hydrodynamic interpretation: Soc. Econ. p. 383-391. Paleontologists and Mineralogists Spec. Pub. Waters, A. C., and Fisher, R. V., 1970, Maar vol- 12, p. 34-52. canoes, Second Columbia River Basalt Sym- Skipper, K., 1971, Antidune cross-stratification in a posium Proc.: Cheney, Eastern Washington turbidite sequence, Cloridorme Formation, State Coll. Press, p. 157-170. Gaspé, Quebec: Sedimentology, v. 17, p. 1971, Base surges and their deposits: 51-68. CapelinhosandTaal Volcanoes: Jour. Geophys. Smith, R. L., 1960, Ash flows: Geol. Soc. America Research, v. 76, p. 5596-5614. Bull., v. 71, p. 795-842. Walker, G.P.L., 1971, Grain-size characteristics of pyroclastic deposits: Jour. Geology, v. 79, p. 696-714. Walker, R. G., 1963, Distinctive types of ripple- MANUSCRIPT RECEIVED BY THE SOCIETY APRIL 7, drift cross-lamination: Sedimentology, v. 2, 1972 p. 173-188. REVISED MANUSCRIPT RECEIVED JULY 13, 1972

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