Anatomy of modern sedimentary volcanoes produced by gas‐charged groundwater liquefaction, Lake Powell, Hite, Utah: Implications for the recognition and interpretation of ancient sedimentary volcanoes

Abstract

Numerous sedimentary volcanoes, recently exposed on the Colorado River delta surface at Lake Powell near Hite, Utah, were generated by sediment slurries propelled by gas, mainly microbially generated methane (CH₄). Two sedimentary volcanoes were excavated, one in 2016 and the other in 2019, in order to characterise the internal structures. Comparison of the internal structures of these features with those of previously documented seismic‐generated sedimentary volcanoes helps in differentiating the various modes of mobilised sediment generation. Sedimentary volcanoes are commonly employed as tools in palaeoseismic reconstruction, thus it is important to establish criteria to differentiate non‐seismic‐generated sedimentary volcanoes and accompanying sediment deformation from those features generated by earthquakes. Trenches through the volcanoes and immediate subsurface areas reveal a complex cone stratigraphy of centimetre‐scale graded sand‐silt laminations and clastic dikes that cross‐cut the cone and sub‐cone (delta) sediment. Some cone strata have ripple cross laminations, a scoured base and are disrupted by soft‐sediment deformation. In the 2016 volcano, the lowest 0.5 m of the dikes exposed in the trench are filled with organic‐rich mud, but these conduits are empty nearer to the surface as a result of sediment settling after eruption cessation. The 2019 sedimentary volcano differs from the other by: (1) more cross laminations in the cone, (2) collapse structures surrounding the crater, (3) a relatively simple plumbing system assisted by desiccation‐generated fissures and (4) a massive sediment infill of the vent. Both complex internal cone stratigraphy and the two distinct cross‐cutting dike‐conduit systems, unequivocally generated by recurrent gas and water discharge, add to the database of features for non‐seismic‐generated sedimentary volcanoes. This array of sedimentary structures from a non‐seismic‐generated sedimentary volcano demonstrates that certain features, including numerous internal laminations composing the cone and complex generations of dike systems are not unique to seismic‐generated sand volcanoes.

INTRODUCTION

Soft-sediment deformation structures (SSDS) are produced when unconsolidated sediment transforms from solid to a liquidised state and becomes capable of flow. This liquidisation occurs when pore-water pressure is increased from liquefaction, a temporary increase of pore-fluid pressure where sediment grains become suspended, and/or fluidisation, fluid flowing vertically through sediment sufficient to exceed grain support, leading to insufficient strength to resist the forces driving it to move (Lowe, 1975; Maltman & Bolton, 2003). Both gas and water fluids can generate SSDS, but only recently have there been studies focussed on differentiating them (Pralle et al., 2003; Frey et al., 2009; Hilbert-Wolf et al., 2016; Wheatley & Chan, 2017).

Sedimentary volcanoes are fabricated by the eruption of assorted mud-size to sand-size sediment slurries that are mobilised by overpressure forces generated by liquefaction and/or fluidisation in the subsurface and migrated through conduits to the surface. Some of the most spectacular geological phenomena, large-scale mud volcanoes, are gas-generated sedimentary volcanoes that develop in hydrocarbon basins from the release of primarily thermogenic methane (Dimitrov, 2003; Mazzini & Etiope, 2017). In some cases, as in Azerbaijan, complex mud volcano systems develop into kilometre-scale features (Roberts et al., 2010). These large-scale mud volcanoes are common features worldwide and collectively are a significant source of atmospheric methane, an important greenhouse gas (Dimitrov, 2003). Biogenic methane produced from the microbial decomposition of organic material sediments in lakes and reservoirs is also an important source of atmospheric methane (Delsontro et al., 2010).

Liquefaction-generated sand volcanoes, also known as sand boils or sand blows, are commonly employed as tools in palaeoseismic reconstruction. These volcanoes along with associated SSDS, such as clastic dikes and sills, are often used to indicate reoccurrence of ancient seismicity and employed to estimate factors such as distance to a palaeoepicentre, minimum seismic event magnitudes and/or to reconstruct recurrence intervals of strong earthquakes (Sieh, 1978; Allen, 1986; Obermeier, 1996; Galli, 2000; Rodríguez-Pascua et al., 2000; Castilla & Audemard, 2007; Hilbert-Wolf et al., 2009; Reicherter et al., 2009; Villamor et al., 2016; Tuttle et al., 2019; Gheibi et al., 2020; Bhadran et al., 2024 and many others). Lacustrine and deltaic sediments are often utilised in palaeoseismic studies (Sims, 1975; Sims & Garvin, 1995; Rodríguez-Pascua et al., 2000; Van Loon & Maulik, 2011; Üner, 2014; Törő & Pratt, 2016; Guo et al., 2023).

However, multiple types of triggers can also develop over-pressured sediments and generate sand volcanoes and other SSDS, including river flooding, gravity flows, artesian conditions and storm waves (Gill & Kuenen, 1957; Burne, 1970; Williams, 1974; Dionne, 1976; Guhman & Pederson, 1992; Holzer & Clark, 1993; Li et al., 1996; Strachan, 2002; Jianhua et al., 2004; Jonk et al., 2007; Netoff et al., 2010; Chen & Lee, 2013; Hilbert-Wolf et al., 2016; Kirkland et al., 2016; Oppo & Capozzi, 2016; Shanmugam, 2017; Wheatley & Chan, 2017). In fact, Shanmugam (2016) suggested that at least 21 triggering mechanisms can generate liquefaction and develop SSDS.

Two sedimentary volcanoes produced by gas and fluid escape were exposed during low water on the Colorado River delta sediments in Lake Powell, Glen Canyon National Recreation Area, Hite, Utah, USA (Figure 1). They were excavated and studied, one in 2016 and the other 2019. Because of the varied, complex sediment make-up of these volcanoes, the term sedimentary volcano best accommodates the grain-size variations and discrepancies between dike and cone compositions that are present across the Lake Powell delta. These sedimentary volcanoes are not seismogenic in origin but rather were produced by liquidisation generated by groundwater flow augmented by shallow production of microbially generated methane (CH₄), carbon dioxide (CO₂) and air degassing through the overlying muds (Malenda et al., 2020). As such, reported here are some of the first documented biogenic methane escape features and increasing the catalogue of gas-related SSDS that is critically needed in order to: (1) distinguish them from seismic-generated volcanoes and (2) differentiate liquid versus gas processes in generating SSDS (see Shanmugam, 2017; Wheatley & Chan, 2017).

[IMAGE OMITTED. SEE PDF]

GEOLOGIC SETTING

Lake Powell was created in 1963 by the pooling of the Colorado River after the completion of the Glen Canyon Dam at Page, Arizona (Figure 1). A swiftly prograding delta developed at the north end of the lake around 1980 as a consequence of the Colorado River's prodigious sediment load coupled with the narrow width of the canyon (Netoff et al., 2010; Johnson et al., 2022; Figure 1). Extended droughts diminished inflow from 2000 to 2005, from 2011 to 2014 and again from 2017 to 2019 resulting in a significant 40 m drop in the lake pool level (Figure 2A). Annual lake-level fluctuations are superimposed on these longer-term changes (see Figure 2B). Due to the rapid base-level drop, the Colorado River channel incised into and exposed the delta plain sediment (Pratson et al., 2008; Johnson et al., 2022).

[IMAGE OMITTED. SEE PDF]

Neither sedimentary volcano was present during fieldwork in May 2014, at the time of extreme low water level (Figure 2). Thus the 2016 volcano, excavated in May 2016, formed between 2014 and 2016, and the 2019 volcano, not existent in May 2016 and trenched in March 2019, developed between 2016 and 2019. Neither volcano was actively effusive during their study. However, while studying the two volcanoes, subaerial volcanoes were observed erupting muddy flows and muddy effusions. Furthermore, visual observations over several hours on different days of active Lake Powell gas vents and mud volcanoes exposed on the land surface indicate that the unsteady erupting flow varies from quiescence to rapid bubbling within the same vent. This may be related to the short-term variations in the release of methane as documented by Malenda et al. (2020).

Information on close-by seismic activity is critical in eliminating a seismic origin for these sedimentary structures. An earthquake magnitude (M) of greater than 5.5 is often cited as a requisite for generating liquefaction and producing sand and mud volcanoes (Allen, 1986; Obermeier, 1996; Galli, 2000; Castilla & Audemard, 2007; Reicherter et al., 2009; Tuttle et al., 2019). In the Lake Powell region, no earthquake larger than 4.0 M has occurred since 1962 (Knudsen et al., 2020). Examination in the United States Geological Survey database of seismic activity in Utah, Colorado and the surrounding environs () indicates that there were no 4.5 or greater magnitude earthquakes within 100 km of the study area for at least 50 years previous to 2020.

The sedimentary volcanoes on the Lake Powell delta developed on a geomorphologically stable topographic low between the Colorado River and the Palaeozoic and Mesozoic rock outcroppings to the east. Beneath the delta, the westward dipping Cedar Mesa Sandstone acts as a confined aquifer sealed by Lake Powell muds (Netoff et al., 2010). During the initial lake-level lowering in 2004 the decrease of hydrostatic pressure and concurrent development of fissures, due to delta collapse as a result of fluvial incision, led to the over-pressured groundwater, augmented by locally derived methane gas, to breach the seal (Netoff et al., 2010). The fluid release led to bulging of the overlying mud, producing including metre to decametre-scale diameter domes, many of which developed into metre-scale sedimentary volcanoes, which ultimately collapsed into craters (pockmarks) (Netoff et al., 2010; Sherrod et al., 2016). Since then, the aquifer discharge has substantially ceased and subsequent (and ongoing ca 2011 to present) SSDS were generated primarily via gas release from shallow organic-rich sediments that produce methane via microbial methanogenesis of organics (Malenda et al., 2020). The later stage SSDS recognised in the delta sediments include pockmarks, salses (gas venting water-filled craters), sedimentary volcanoes (including the cones described here) and gas bubble cavities (Netoff et al., 2010; Sherrod et al., 2016; Miller et al., 2018).

METHODS

Both mud volcanoes were trenched to about halfway between the crater and the outer edge. Sediment samples were collected from various components of the sedimentary volcanoes as well as the source (delta) bed. The trenches were then extended further back to reach the crater and expose the feeder conduit (‘plumbing’) system. The samples collected in the field were brought back to Central Connecticut State University where the grain size was analysed with a Malvern Mastersizer 3000 (Figure 3). The instrument utilises laser diffraction to optically measure particles between 0.01 and 2000 μm in size. Samples were immersed in a dispersing agent (40 g/L of sodium hexametaphosphate) and subjected to an ultrasonic vibrator for 5 min to facilitate dispersion before grain-size analysis. The Mastersizer 3000 apparatus provides the median diameter and the percentages of the related size fractions of a sample with a relative error of less than 1%. Standard loss on ignition tests, were performed to determine the organic matter content of each sample. Photographs of the trench walls of the volcano were analysed and line-drawing overlays were created using Adobe Illustrator. The line drawings outline the internal stratigraphy, the internal plumbing system and significant internal features such as vents, clastic dikes and sills, and sedimentary structures within the cone and underlying strata.

RESULTS

Both volcanoes are similar in size and external morphology except that in plan view the 2016 volcano has a distinct elliptical shape compared to the circular 2019 volcano. The grain size and internal structures of the two cones are similar, however, the geometry and sediment fill of the plumbing systems for each volcano are significantly different.

2016 sedimentary volcano

The long axis of the elliptical-shaped cone is aligned along the flow direction of the Colorado River and asymmetrically elongated in the downflow direction (Figure 4A). The diameter of the cone is 1.5 m from margin to margin measured along the trench that was excavated parallel to the elongation direction and 1.2 m perpendicular to the trench. At the crest, the cone is about 7 cm higher than the underlying desiccated muds. The cone's crater is 20 cm in diameter and 6 cm deep with a smaller 3 cm diameter vent centrally located within the crater (Figure 5).

[IMAGE OMITTED. SEE PDF]

[IMAGE OMITTED. SEE PDF]

[IMAGE OMITTED. SEE PDF]

Trenching exposed three units, from the bottom of the trench to the top: (1) a black organic-rich silty mud layer (total thickness was not determined due to the water level in the trench but was constrained to be at a minimum of 20 cm), (2) 0.5–0.7 m of black to brown mud and (3) sand of the volcano edifice (Figures 4, 5 and 6). The basal black organic-rich mud contains 1 cm thick lenses of macerated plant material and small pieces of fragmented wood.

[IMAGE OMITTED. SEE PDF]

A complex subsurface plumbing system revealed in the trench consists of several subvertical conduits (Figures 4C, 5 and 6). The lower portions of the various conduits are filled with black organic-rich silt, clay and abundant plant debris (Figures 4C and 6A,B). Each conduit consists of an open (void) upper portion, up to 40 cm long and 1–3 cm wide, that directly connects to a lower sediment-filled dike, more than 30 cm deep (Figures 4 and 5). Some of the conduits link with other conduits, such as those that form the volcano vent (Figure 6C,D). The sediment-filled dikes were traced directly into the underlying black organic-rich silty mud layer, but could not be traced below because of the limit of trenching (Figures 4 and 5). The mud layer is the source of sediment that partially fills the conduits (Figure 5) and probably the source of methane-rich gas (Malenda et al., 2020).

The plumbing system that feeds the volcano vent is comprised of interconnected, irregularly shaped, vertical and lateral branching conduits/dikes. Only one of the conduits was observed to breach the vent surface (Figure 5). The feeder system is offset to the side of the crater and not located directly beneath the vent, illustrating the convoluted pathway of the gas migration (Figure 5). Another open conduit appears to be connected to the crater, but there is no evidence that effusive products were emitted to the vent surface from it. Conduit walls are smooth in the basal sediment-filled dike segment and become more branching and irregularly shaped, with highly crenulated margins upwards in the open void zone (Figure 6). Tens of centimetres away from the vent, but still within the edifice perimeter, are complex, organic-rich, black, silt and mud-filled dikes that also lack sediment fill in their upper reaches and cross-cut the internal stratification of the cone as a series of open fractures (Figures 4 and 6). The black silts forming the walls of the conduit are discoloured to brown adjacent to the open and sediment-filled portions of the conduits (Figures 4 and 6).

The internal stratigraphy of the cone flanks revealed in the trench consists of eight normally graded couplets that vary in thickness from 4 to 7 mm (Figure 6C,D). The couplets are characterised by parallel-laminated fine sands with sharp bases overlain by parallel-laminated fine sands to silts (Figure 3) that downlap onto the underlying older desiccated delta silts (Figure 6C,D). The only erosional scour recognised in the stratigraphy is at the top of couplet 6 (counted from the base). Couplet 6 is locally fully truncated by a low-angle scour and overlain by dark silts followed by couplet 7, which is thickened over the erosional depression. The open conduits that cross-cut the cone flanks have SSD consisting of anticlinal folds and loads on their margins (Figure 6C,D).

2019 sedimentary volcano

The external shape of the cone is nearly circular with a diameter of about 2 m (Figure 7A). The cone extends up to 12 cm above the delta surface. The cone's centrally located crater is 25 cm in diameter and 7 cm deep. The crater is partially filled in with sediment, but a 20 × 10 cm elliptical depression manifests the vent. Margins of the crater have superimposed rill features. Five radial cracks extend outward from the crater as parts of large polygons near the crater, but smaller polygons are developed towards the outer cone (Figure 7A). Crack margins are modified by high-angle rill features. At the margins of the volcano, strands of effluent extend outwards in the floors into the bases of the surrounding mud cracks (Figure 7A).

The sedimentary volcano developed on extensively mud-cracked delta surface muds (Figures 7 through 10). Diffuse layers of delta sediments exposed in the trench consist of brown to reddish-brown poorly sorted muds with grain-size distributions exhibiting bimodal peaks of silt and clay (Figures 3 and 8). Mud cracks extend up to 15 cm into the delta sediments and primarily structureless mud fills the base; parallel laminations are abundant near the top of the fill (Figures 8, 9 and 10). Laminations are similar in appearance and grain size (Figure 3) to the laminations associated with the cone. Excavations reveal the merger of two v-shaped structures producing a hanging pendant of delta sediments (Figure 9). At the base of the trench, a white laminated, very fine-grained sand and silt layer (Figure 3) is broadly folded, exhibits flame and load structures, and is cross-cut by muds (Figures 9 and 10).

[IMAGE OMITTED. SEE PDF]

[IMAGE OMITTED. SEE PDF]

[IMAGE OMITTED. SEE PDF]

[IMAGE OMITTED. SEE PDF]

Offset from the cone crater is a 10 cm wide conduit, probably arising from the mud-ejecting source, slightly coarser than the surrounding delta sediment (Figures 4, 10 and 11). The conduit, stretching 10 cm across, is filled in with massive sediments, differing from the internal fill of the other downward tapering fissures with stratigraphically lower tops (Figures 10 and 11). This fill extends to the base of the crater. The conduit cross-cuts rotated down-dropped blocks of flanking sediment. The sediment within the conduit is coarser than the surrounding bimodal deltaic sediments, with an average grain size of medium silt (Figure 3). The organic carbon of the sediment from the conduit is similar to that of the delta muds, mud-crack fillings and cone laminae, all ca 1.5–2.0%.

[IMAGE OMITTED. SEE PDF]

The internal stratigraphy of the cone flanks revealed in the trenches consists of two scales of features, larger scale normally graded couplets that vary in thickness from 1 to 2 cm (Figures 9, 10 and 12) and smaller laminations that subdivide the larger scale couplets (Figure 12C). The 2016 volcano only has the smaller laminations. The larger scale couplets are composed of groupings of parallel-laminated very fine sand and silts with sharp, often erosional, bases overlain by parallel-laminated to structureless clayey silts. Thickness varies along the length of these smaller couplets; the number of laminations varying along the length with numbers reducing distally. There are six well-developed couplets comprising the cone with several smaller and laterally discontinuous ones (Figure 12). The mean grain size of the cone laminations is fine silt, similar to the lower deltaic sediment (Figure 3). Laminations thicken near mid-cone and taper towards the periphery where they are best defined. The couplets contain ripple cross laminations, more abundant towards the crater, SSD, scour bases and syndepositional faults (Figure 12). In addition, scoured bases are more common and more deeply down cut towards the crater.

[IMAGE OMITTED. SEE PDF]

INTERPRETATION: FORMATION OF THE SEDIMENTARY VOLCANOES

With the 2016 volcano situated at 1089 m elevation while the 2019 is at 1087 m, lake-level data and field observations indicate the sedimentary volcanoes developed subaqueously (Figure 2). The following observations support this assertion: (1) the observed subaerial volcanoes erupt muddy flows and muddy effusions; (2) there is no obvious source of sand-dominated sediment observed in the trenches, but sand is diffuse throughout the black and brown organic muds of the delta sediments indicating potential concentration through winnowing; (3) normally graded, well-developed, clayey silt caps to the cone strata; and (4) the 2016 sedimentary volcano has an asymmetry and elongation axis that parallels the Colorado River course thus indicating the sand volcano eruption was interacting with a weak southward-flowing unidirectional current. Burne (1970) recognised a similar cone asymmetry in sedimentary volcanoes developed on subaqueous mass flow beds and attributed the shape to shearing by weak residual currents. The 2019 sedimentary volcano does not exhibit cone asymmetry, but the well-developed clayey silt caps to the cone strata suggest they were also developed subaqueously, probably in ponded water.

The irregular-shaped, multi-cavity conduit-dike system in the 2016 volcano formed as groundwater, pressurised by microbially generated methane gas (Malenda et al., 2020), moved upwards, developing several pathways towards the surface. A second vent may have been present and, if active, was subsequently sealed (Figure 5). After the initial eruption ceased, the remaining material in the conduits settled downward and sealed the vents providing resistance, allowing the pressure to build up for a subsequent eruption phase and further dike and conduit development. This process was repeated several times in both volcanoes, as evidenced by the multiple graded beds recognised in the internal strata of the cones. Fracture development continued after the 2016 sedimentary volcano formation as evidenced by fractures (conduits) that cross-cut the edifice (Figures 4, 5 and 6). For the 2019 sedimentary volcano, only one conduit penetrated the strata from below the cone and that apparently utilised a large mud crack to breach the surface (Figures 10 and 11). The apparent conduit mud crack widened and experienced collapse of the surrounding rim (Figure 10).

The graded beds in the Lake Powell sedimentary volcano cones are interpreted to record temporal variations in gas and fluid flow out of the conduit. The reductions in lake level that took place during its formation do not match the number of internal laminations present in the cones (6–8), hence annual lake-level change is not a viable causal mechanism.

The short-term unsteady emissions from the active Lake Powell gas vents and mud volcanoes exposed on the land surface suggest the possibility of gas-charged sporadic eruptive flows. Over a much larger time frame, methane release from large deep-water lacustrine pockmarks has shown to be unsteady over thousands of years resulting in episodic Holocene sediment movement (Loher et al., 2016).

Intrusion of the organic-rich mudstone into the 2016 conduits indicates subsurface mobilisation of the underlying organic-rich mudstone occurred via gas and fluid migration (see Van Rensbergen et al., 2003). It is inferred that initial flow out of the vent contained both muds and sands; muds were ejected into the water column, the Colorado River current incorporated the silts and muds from the volcano effluent, transporting most of the finer-grained materials down river as suspended sediment and leaving silt and sand-rich sediment proximal to the vent to form a sand-dominated cone (Figure 3). This winnowing effect generated a cone consisting of sediment coarser than the effluent as represented by the sediment present in the dike conduits. Sand, winnowed from the organic-rich source bed flowed out of the crater overtopping the rim as high-density sand-rich sediment flows down the flanks similar to features and mechanisms described by Loher et al. (2016) and, in the case of 2019, more tractional flows characterise the crater rim area.

During development and expansion of the 2019 cone, mud cracks were filled with laminated sediment flowing out of the newly formed crater. Non-laminated sediment comes from the margin of the cracks by breakdown of the crack walls by wind and water movement or sedimentation from the overlying water column. The latter source probably filled the base of the large mud crack-fill when the area was resubmerged before the initial expulsion of the volcano. Because of the few metres of relief on the delta top, this filling of the large mud cracks from ponded lake sediment occurred only in the lower elevations. Where the elevation is slightly lower on the delta surface, it was resubmerged and the large cracks filled (Figure 7C), whereas those in the higher elevation surfaces were not (Figure 7B).

DISCUSSION

The vertical movement of liquid and gas in marginal lacustrine and deltaic settings is commonplace and produces large-scale SSDS, such as pockmarks, similar to those generated in marine settings (Dragantis & Janda, 2003; Duck & Herbert, 2006; Netoff et al., 2010; Bussman et al., 2011; Loher et al., 2016; Sherrod et al., 2016). Deep aquifers underlying modern lakes can generate subaqueous springs that influence sedimentation associated with pockmarks over a thousand's of years timeframe (Matter et al., 2010; Morellón et al., 2014; Ross et al., 2014). Wheatley and Chan (2017) proposed that considerable variation in geometry for larger conduits is produced by different types of fluid expulsion: cone-shaped for gas and more pipe-like for liquids. Although not as well-documented, small-scale sedimentary structures generated by vertical gas and fluid movement have been characterised by theoretical, experimental and field investigations (Nichols et al., 1994; Owen, 1996; Dragantis & Janda, 2003; Frey et al., 2009; Hilbert-Wolf et al., 2016; Miller et al., 2018).

The liquefaction origin and structure of seismically generated sand volcanoes is reasonably well understood (Saucier, 1989; Sims & Garvin, 1995; Jonk et al., 2007; Pringle et al., 2007; Reid et al., 2012; Quigley et al., 2013; Simpson et al., 2013; Rodríguez-Pascua et al., 2015; Tian et al., 2016; Tuttle et al., 2017; Maurer et al., 2019).

Internal cone stratigraphies of reported seismogenetic sand volcanoes vary from one layer to multiple stacked layers (Saucier, 1989; Sims & Garvin, 1995; Jonk et al., 2007; Pringle et al., 2007; Quigley et al., 2013; Simpson et al., 2013; Rodríguez-Pascua et al., 2015). From the 2010 to 2011 Christchurch, New Zealand, earthquake sequence, Quigley et al. (2013) report layers with very limited development of small-scale cross stratification capping stacked graded beds composing the sand volcanoes. Each graded bed relates to a specific seismic event that initiates a new discrete phase of liquefaction and extrusion (see Quigley et al., 2013 their Figure 2G). Maurer et al. (2019) also recognised recurrent liquefaction and eruption events in the sedimentary volcanoes developed during the Christchurch events, each manifested by centimetre-thick silt drapes. In contrast, Rodríguez-Pascua et al. (2015) interpret multiple graded beds consisting of ripple laminations overlain by silt within large fissure sand volcanoes as the product of evolving ground deformation related to a single 2012 seismic event in Italy.

In a non-seismic gas source involving modern flooding of the Mississippi River, Li et al. (1996) documented banding consisting of alternating sand and silty sand composing the sand volcano. In this setting, the sand source bed is within 0.3 m of the surface and the feeder system cross-cuts a silty sand layer composing the original ground surface.

In the late Permian of India, Van Loon and Maulik (2011) identified a suite of eroded sand volcano forms, all of which contained what appears to be a single graded bed and diffuse internal laminations composing the cone. Similarly, several studies have documented a single layer composing the seismic-related sand volcano cones from the rock record that contrasts with the multiple layers composing the Lake Powell sedimentary volcanoes (Jonk et al., 2007; Pringle et al., 2007; Simpson et al., 2013).

Overall, the similarities of scale and the strata comprising sedimentary volcanic cones from both seismically triggered and non-seismically generated liquefaction events preclude establishing definitive criteria for distinction. Furthermore, although the preservation potential for subaqueous lacustrine sedimentary volcanic cones is relatively good, in most sedimentary environments the cones would probably erode over time (Li et al., 1996; Van Loon & Maulik, 2011; Reid et al., 2012). However, the sub-cone SSDS in most settings would have a much greater potential for stratigraphic preservation.

Clastic dikes and sills are common sub-cone features in seismic-generated sedimentary volcanoes. The most common plumbing system within these volcanoes consists of a subvertical feeder dike that widen downwards or has parallel walls, and appears approximately linear in plan view (Obermeier, 1996). Multiple volcanoes, often elongated, may develop along fissures caused by lateral ground spreading (Sims & Garvin, 1995; Reid et al., 2012; Loope et al., 2013; Quigley et al., 2013; Rodríguez-Pascua et al., 2015; Tuttle et al., 2017). Reid et al. (2012) reported widened funnel-shaped openings to cylindrical feeder pipes, however the shallow water table precluded a deeper search for planar structures. More complex plumbing systems are also common, generated by seismogenic liquefaction with sills forming in weaker thin sand or silt layers between clay layers through which dikes develop (Saucier, 1989; Obermeier, 1996). Groundwater-charged sand volcanoes typically have cylindrical sand-filled feeder pipes (Guhman & Pederson, 1992; Li et al., 1996; Wheatley & Chan, 2017), however, Holzer and Clark (1993) reported sand volcanoes developing from aquifer discharge along a 500 m long fissure.

The Lake Powell 2019 sedimentary volcano exhibits complex dike feeder systems that do not widen downwards, have parallel walls and are not linear in plan view (Figures 4 and 5). The 2019 feeder system is poorly developed, relatively simple and the liquefied sediment appears to have benefited from the deep mud cracks to access the surface. Larger scale fissures developed in the study area with slumping and spreading of the sediment caused by the loss of lateral support as a result of the down-cutting of the Colorado River into the delta (Netoff et al., 2010). Although the sedimentary volcanoes that developed on the delta are not associated with surface fissures, the linear alignment of the volcanoes and pockmarks (see Sherrod et al., 2016, Figure 4B), indicate that fissures have probably influenced the development and arrangement of these features.

The dike fill in seismically induced sand volcanoes consists primarily of sands as liquefaction most readily acts on coarser sediments. Silty, very-fine sand is the finest sediment in which large seismically induced liquefaction features commonly form in the field (Obermeier, 1996). As little as 5% clay or silt-sized material in a sand deposit can make liquefaction significantly less likely than for the same deposit lacking finer grains (Obermeier, 1996). Because finer-grained sediments are more prone to cohesion, the rearrangement of particles becomes increasingly challenging impeding liquefaction. Furthermore, the sediment within seismically generated volcano dike systems fines upwards (Obermeier, 1996). The sediment size of conduit fills within the Lake Powell volcanoes varies for each volcano, but does not fine upwards. Conduit fills in seismic sedimentary volcanoes often contain brecciated clasts of the sidewall material within the dike and at the base of the cone (Saucier, 1989; Obermeier, 1996; Loope et al., 2013; Tuttle et al., 2017). This feature is often associated with seismic sand volcanoes, a result of sudden violent mobilisation and extrusion of material, but is rarely associated with non-seismic sedimentary volcanoes (Li et al., 1996). No clasts of the vent sidewalls were observed in the 2016 or 2019 Lake Powell volcanoes. Additionally, the vertical connection between a sediment-filled dike and open conduit fracture system appears not to have been previously reported from seismically generated sand volcanoes (Li et al., 1996; Obermeier, 1996; Rossetti, 1999; McCalpin, 2009; Reicherter et al., 2009; Hilbert-Wolf et al., 2016). The internal structure and sediment fill of the volcano feeder systems are potentially distinguishing criteria, but needs further investigation.

SUMMARY AND CONCLUSION

The Colorado River delta in Lake Powell exhibits several SSD features, including the two sedimentary volcanoes (one studied in 2016 and the other in 2019) reported in this paper. These volcanoes are not seismogenic in origin but were generated by biogenic gas-charged groundwater that produced liquefaction of subsurface delta sediment. Both volcanoes have been interpreted to be deposited subaqueously, however, the 2016 volcano was probably deposited in flowing water as indicated by the elongated external shape and coarse grain size. Dissimilarly, the 2019 volcano was probably deposited in still water as indicated by its finer grain size and circular external shape. The two volcanoes were trenched to study the internal structure of the cone and sub-cone sediments. The cones of the volcanoes consist of normally graded very-fine sand and silt laminations. Nearby volcanoes and pockmarks undergo intermittent bubbling, which all indicate non-steady gas and fluid discharge and support an expulsion pulse responsible for depositing individual graded layers. The internal plumbing of each volcano differs dramatically. The volcano trenched in 2016 contains a very complex feeder conduit system that cross-cuts the delta sediment and sand volcano cone. The bottom portions of the conduits are filled with mud and the top portions remain free of sediment. The walls are very irregular and the whole feeder system is offset to the side of the crater, rather than directly below it. This differs from the 2019 volcano that has a much less complex feeder system. The 2019 cone exhibits a relatively simple feeder system consisting of one main conduit filled with sediment directly beneath the crater, and that utilised the deep mud cracks on the delta surface. At some point, a wide chamber developed beneath the crater and subsequently collapsed into the vent.

This assemblage of SSDS from a methane-groundwater generated sedimentary volcano demonstrates that certain features, including numerous internal laminations comprising the cone and complex generations of dike systems are not unique to seismic-generated sand volcanoes. Non-seismic sedimentary volcanoes may also contain complex internal cone stratigraphy and complex dikes, internal features that closely mimic those generated by seismic events. Previously established criteria depicting features of seismic sedimentary volcanoes must be applied cautiously in differentiating seismic from non-seismic volcanoes. The internal structure and sediment fill of the feeder conduit systems in the two Lake Powell sedimentary volcanoes documented in this study contribute to the knowledge base of distinguishing criteria.

ACKNOWLEDGEMENTS

This work was supported by grants from the Kutztown University Research Committee, the Pennsylvania State System of Higher Education Professional Development Committee, and the CSU-AAUP Faculty Research Grant program. Jim Kirkland is thanked for his encouragement and pointing us in the direction of the project. The aid of John Spence, Chief Scientist of the National Park Service at Glen Canyon throughout our work is greatly appreciated. We thank reviewers Cari Johnson and Cecilia Benavente and the journal editorial staff for their help in improving the manuscript.

CONFLICT OF INTEREST STATEMENT

The authors have no conflicts of interest to declare.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.

References

Allen, J.L.R. (1986) Earthquake magnitude‐frequency, epicentral distance and soft‐sediment deformation in sedimentary basins. Sedimentary Geology, 46, 67–75.

Bhadran, A., Duarah, B.P., Girishbai, D., Raza, M.A., Mero, A., Lahon, S., Achu, A.L. & Gopinath, G. (2024) Soft sediment deformation structures from the Brahmaputra Basin: a window to the eastern Himalayan paleoseismicity and tectonics. Journal of Asian Earth Sciences, 259, [eLocator: 105894].

Burne, R.V. (1970) The origin and significance of sand volcanoes in the Bude Formation (Cornwall). Sedimentology, 15, 211–228.

Bussmann, I., Schlömer, S., Schlüter, M. & Wessels, M. (2011) Active pockmarks in a large lake (Lake Constance, Germany): effects on methane distribution and turnover of sediment. Limnology and Oceanography, 56, 379–393.

Castilla, R.A. & Audemard, F.A. (2007) Sand blows as a potential tool for magnitude estimation of pre‐instrument earthquake. Journal of Seismology, 17, 741–749.

Chen, J. & Lee, H.S. (2013) Soft‐sediment deformation structures in Cambrian siliciclastic and carbonate storm deposits (Shandong Province, China): differential liquefaction and fluidizaion triggered by storm‐wave loading. Sedimentary Geology, 288, 81–94.

DelSontro, T., McGinnis, D.F., Sobek, S., Ostrovsky, I. & Wehrli, B. (2010) Extreme methane emissions from a Swiss hydropower reservoir: contribution from bubbling sediments. Environmental Science and Technology, 44, 2419–2425.

Dimitrov, L.I. (2003) Mud volcanoes—a significant source of atmospheric methane. Geo‐Marine Letters, 23, 155–161.

Dionne, J.‐C. (1976) Miniature mud volcanoes and other injection features in tidal flats, James Bay, Québec. Canadian Journal of Earth Sciences, 13, 422–428.

Dragantis, E. & Janda, C. (2003) Subaqueous artesian springs and associated spring pits in a Himalayan pond. Boreas, 32, 436–442.

Duck, R.W. & Herbert, R.A. (2006) High‐resolution shallow seismic identification of gas escape features in the sediments of Loch Tay, Scotland: tectonic and microbiological associations. Sedimentology, 53, 481–493.

Frey, S.E., Gingras, M.K. & Dashtgard, S.E. (2009) Experimental studies of gas‐escape and water‐escape structures. Journal of Sedimentary Research, 79, 808–816.

Galli, P. (2000) New empirical relationships between magnitude and distance for liquefaction. Tectonophysics, 324, 169–187.

Gheibi, E., Gassman, S. & Talwani, P. (2020) Regional assessment of prehistoric earthquake magnitudes in the South Carolina Coastal Plain. Bulletin of Engineering Geology and the Environment, 79, 1413–1427.

Gill, W.D. & Kuenen, P.H. (1957) Sand volcanoes on slumps in the Carboniferous of County Clare, Ireland. Quarterly Journal of the Geological Society, 113, 441–460.

Guhman, A.I. & Pederson, D.T. (1992) Boiling sand springs, Dismal River, Nebraska: agents for formation of vertical cylindrical structures and geomorphic change. Geology, 20, 8–10.

Guo, L., He, Z. & Li, L. (2023) Lacustrine sedimentary responses to earthquakes—soft‐sediment deformation structures since late Pleistocene: a review of current understanding. Earthquake Research Advances, 3, [eLocator: 100158].

Hilbert‐Wolf, H.L., Roberts, E.M. & Simpson, E.L. (2016) New sedimentary structures in seismites from SW Tanzania: evaluating gas‐ vs. water‐escape mechanisms of soft‐sediment deformation. Sedimentary Geology, 344, 253–262.

Hilbert‐Wolf, H.L., Simpson, E.L., Simpson, W.S., Tindall, S.E. & Wizevich, M.C. (2009) Insights into syndepositional fault movement in a foreland basin: trends in seismites of Upper Cretaceous Wahweap Formation, Kaiparowits Basin, Utah, U.S.A. Basin Research, 21, 856–871.

Holzer, T.L. & Clark, M.M. (1993) Sand boils without earthquakes. Geology, 21, 873–876.

Jianhua, Z., Zhifeng, W., Guanmin, W., Xiban, W., Hongbo, L. & Xiaohua, S. (2004) Air‐discharge pits on the Yellow River delta plain. Sedimentary Geology, 170, 1–20.

Johnson, C., Root, J.C., Hynek, S. & Schmidt, J.J.C. (2022) Sedimentary record of annual‐decadal timescale reservoir dynamics: anthropogenic stratigraphy of Lake Powell, Utah, USA. The Sedimentary Record, 20, 15–29.

Jonk, R., Cronin, B.T. & Hurst, A. (2007) Variations in sediment extrusions in basin‐floor, slope, and delta‐front settings: sand volcanoes and extruded sand sheets from the Namurian of County Clare, Ireland. In: Hurst, A. & Cartwright, J. (Eds.) Sand injectites: implication for hydrocarbon exploration and production, vol. 87. Tulsa, OK: AAPG Special Publication, pp. 221–226.

Kirkland, J.I., Simpson, E.L., DeBlieux, D.D., Madsen, S.K., Bogner, E. & Tibert, N.E. (2016) Depositional constraints on the Lower Cretaceous Stikes Quarry dinosaur site: upper Yellow Cat Member, Cedar Mountain Formation, Utah. Palaios, 31, 421–439.

Knudsen, T.R., Hiscock, A.I., Lund, W.R. & Bowman, S.D. (2020) Geologic hazards of the Bullfrog and Wahweap high‐use areas of the Glen Canyon National Recreation Area, San Juan, Kane, and Garfield Counties, Utah, and Coconino County, Arizona, vol. 166. Salt Lake City: Utah Geological Survey Special Study, p. 66.

Li, Y., Craven, J., Schweig, E.S. & Obermeier, S.F. (1996) Sand boils induced by the 1993 Mississippi River flood: could they one day be misinterpreted as earthquake‐induced liquefaction? Geology, 24, 171–174.

Loher, M., Reusch, A. & Strasser, M. (2016) Long‐term pockmark maintenance by fluid seepage and subsurface mobilization – sedimentological investigation in Lake Neuchâtel. Sedimentology, 63, 1168–1186.

Loope, D.B., Elder, J.F., Zlotnik, V.A., Kettler, R.M. & Pederson, D.T. (2013) Jurassic earthquake sequence recorded in multiple generations of sand blows, Zion National Park, Utah. Geology, 41, 1131–1134.

Lowe, D.R. (1975) Water escape structures in coarse‐grained sediments. Sedimentology, 22, 157–204.

Malenda, M., Betts, T.A., Simpson, W.S., Wizevich, M.C., Simpson, E.L. & Sherrod, L. (2020) Methane emissions from muds during low water‐level stages of Lake Powell southern Utah, USA. Geology of the Intermountain West, 7, 97–112.

Maltman, A.J. & Bolton, A. (2003) How sediments become mobilized, vol. 216. London: Geological Society Special Publication, pp. 9–20.

Matter, M., Anselmetti, F.S., Jordanoska, B., Wagner, B., Wessels, M. & Wüest, A. (2010) Carbonate sedimentation and effects on eutrophication observed at the Kališta subaquatic springs in Lake Ohrid (Macedonia). Biogeosciences, 7, 3755–3767.

Maurer, B.W., Green, R.A., Wotherspoon, L.M. & Bastin, S. (2019) The stratigraphy of compound sand blows at sites of recurrent liquefaction: implications for paleoseismicity studies. Earthquake Spectra, 35, 1421–1440.

Mazzini, A. & Etiope, G. (2017) Mud volcanism: an updated review. Earth‐Science Reviews, 168, 81–112.

McCalpin, J.P. (2009) Paleoseismology. In: International geophysics, vol. 95, 3rd edition. Cambridge, MA: Academic Press, p. 648.

Miller, K., Simpson, E.L., Sherrod, L., Wizevich, M.C., Malenda, M., Morgano, K., Richardson, A., Livingston, K.A. & Bogner, E. (2018) Gas bubbles in deltaic muds, Lake Powell delta, Glen Canyon National Recreation Area, Hite, Utah. Marine and Petroleum Geology, 92, 904–912.

Morellón, M., Anselmetti, F.S., Valero‐Garcés, G.S., Ariztegui, D., Sáez, A., Pilar Mata, M., Barreiro‐Lostres, F., Rico, M. & Moreno, A. (2014) The influence of subaquatic springs in lacustrine sedimentation: origin and paleoenvironmental significance of homogeneities in karstic Lake Banyoles (NE Spain). Sedimentary Geology, 311, 96–111.

Netoff, D., Baldwin, C.T. & Dohrenwend, J. (2010) Non‐seismic origin of fluid/gas escape structures and lateral spreads on the recently exposed Hite delta, Lake Powell, Utah—preliminary findings. In: Carney, S.M., Tabet, D.E. & Johnson, C.L. (Eds.) Geology of South‐Central Utah, vol. 39. Salt Lake City: Utah Geological Association Publication, pp. 61–92.

Nichols, R.J., Sparks, S.J. & Wilson, C.J.N. (1994) Experimental studies of the fluidization of layered sediments and the formation of fluid escape structures. Sedimentology, 41, 233–253.

Obermeier, S.F. (1996) Using liquefaction‐induced features for paleoseismic analysis: an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of Holocene paleo‐earthquakes. Engineering Geology, 44, 1–76.

Oppo, D. & Capozzi, R. (2016) Spatial association of mud volcano and sandstone intrusions, Boyadag anticline, western Turkmenistan. Basin Research, 28, 827–839.

Owen, G. (1996) Experimental soft‐sediment deformation structures formed by liquefaction of unconsolidated sands. Sedimentology, 43, 279–293.

Pralle, N., Külzer, M. & Gudehus, G. (2003) Experimental evidence on the role of gas in sediment liquefaction and mud volcanism. In: Hillis, R.R., Maltman, A.J., Morely, C.K. & Van Rensbergen, P. (Eds.) Subsurface sediment mobilization, vol. 216. London: Geological Society Special Publication, pp. 159–171.

Pratson, L., Hughes‐Clarke, J., Anderson, M., Gerber, T., Twichell, D., Ferrari, R., Nittrouer, C., Beaudoin, J., Granet, J. & Crockett, J. (2008) Timing and patterns of basin infilling as documented in Lake Powell during a drought. Geology, 36, 843–846.

Pringle, J.K., Westerman, A.R., Stanbrook, D.A., Tatum, D.I. & Gardiner, A.R. (2007) Sand volcanoes of the Carboniferous Ross Formation, County Clare, Western Ireland: 3‐D internal sedimentary structures and formation. In: Hurst, A. & Cartwright, J. (Eds.) Sand injectites: implications for hydrocarbon exploration and production, vol. 87. Tulsa, OK: AAPG Special Publication, pp. 227–231.

Quigley, M.C., Bastin, S. & Bradley, B.A. (2013) Recurrent liquefaction in Christchurch, New Zealand, during the Canterbury earthquake sequence. Geology, 41, 419–422.

Reicherter, K., Michetti, A.M. & Silva, P.G. (Eds.). (2009) Palaeoseismology: historical and prehistoricial records of earthquake ground effects for seismic hazard assessment, vol. 316. London: The Geological Society Special Publication, p. 324.

Reid, C.M., Thompson, N.K., Irvine, J.R.M. & Laird, T.E. (2012) Sand volcanoes in the Avon–Heathcote Estuary produced by the 2010–2011 Christchurch Earthquakes: implications for geological preservation and expression. New Zealand Journal of Geology and Geophysics, 55, 249–254.

Roberts, K.S., Davies, R.J. & Stewart, S.A. (2010) Structure of exhumed mud volcano feeder complexes, Azerbaijan. Basin Research, 22, 439–451.

Rodríguez‐Pascua, M.A., Calvo, J.P., De Vicente, G. & Gómez‐Gras, D. (2000) Soft‐sediment deformation structures interpreted as seismites in lacustrine sediments in the Prebetic Zone, SE Spain, and their potential use as indicators of earthquake magnitudes during the Late Miocene. Sedimentary Geology, 135, 117–135.

Rodríguez‐Pascua, M.A., Silva, P.G., Pérez‐López, R., Giner‐Robles, J.R., Martin‐González, F. & Del Moral, B. (2015) Polygenetic sand volcanoes: on the features of liquefaction processes generated by a single event (2012 Emila Romagna 5.9 M_w earthquake, Italy). Quaternary International, 357, 329–335.

Ross, K.A., Smets, B., de, M., Hilbe, M., Schmid, M. & Anselmetti, F. (2014) Lake‐level rise in the late Pleistocene and active subaquatic volcanism since the Holocene in Lake Kivu, East African Rift. Geomorphology, 221, 274–285.

Rossetti, D.F. (1999) Soft‐sediment deformation structures in Late Albian to Cenomanian deposits, Sãn Luís Basin, northern Brazil: evidence for paleosismicity. Basin Research, 46, 1065–1081.

Saucier, R.T. (1989) Evidence for episodic sand‐blow activity during the 1811‐1812 New Madrid (Missouri) earthquake series. Geology, 17, 103–106.

Shanmugam, G. (2016) The seismite problem. Journal of Palaeogeography, 5, 318–362.

Shanmugam, G. (2017) Global case studies of soft‐sediment deformation structures (SSDS): definitions, classifications, advances, origins, and problems. Journal of Palaeogeography, 6, 251–320.

Sherrod, L., Simpson, E.L., Higgins, R., Miller, K., Morgano, K., Snyder, E. & Vales, D. (2016) Subsurface structure of water–gas escape features revealed by ground‐penetrating radar and electrical resistivity tomography, Glen Canyon National Recreation Area, Lake Powell delta, Utah, USA. Sedimentary Geology, 344, 160–174.

Sieh, K.E. (1978) Prehistoric large earthquakes produced by slip on the San Andreas fault at Pallett Creek, California. Journal of Geophysical Research: Solid Earth, 83(B8), 3907–3939.

Simpson, E.L., Hilbert‐Wolf, H.L., Wizevich, M.C. & Tindall, S.E. (2013) Implications of the internal plumbing of a Late Cretaceous sand blow: Grand Staircase‐Escalante National Monument, Utah. In: Titus, A. & Lowen, M.A. (Eds.) At the top of the grand staircase—the Late Cretaceous of Southern Utah. Bloomington IN: University Press, pp. 74–84.

Sims, J.D. (1975) Determining earthquake recurrence intervals from deformational structures in young lacustrine sediments. Tectonophysics, 29, 141–153.

Sims, J.D. & Garvin, C.D. (1995) Recurrent liquefaction induced by the 1989 Loma Prieta earthquake and 1990 and 1991 aftershocks: implications for paleoseismicity studies. Bulletin of the Seismological Society of America, 85, 51–65.

Strachan, L.J. (2002) Slump‐initiated and controlled syndepositional sandstone remobilization: an example from the Namurian of County Clare, Ireland. Sedimentology, 49, 25–41.

Tian, H., Zhang, S. & Zhang, A. (2016) Test investigation on liquefied deformation structure in saturated lime‐mud composites triggered by strong earthquakes. Acta Geologica Sinica, 90, 2008–2021.

Törő, B. & Pratt, B.R. (2016) Sedimentary record of seismic events in the Eocene Green River Formation and its implications for regional tectonics on lake evolution (Bridger Basin, Wyoming). Sedimentary Geology, 344, 175–204.

Tuttle, M.P., Villamor, P., Almond, P., Bastin, S., Giona Bucci, M., Langridge, R. & Hardwick, C.M. (2017) Liquefaction induced during the 2010–2011 Canterbury, New Zealand, earthquake sequence and lessons learned for the study of paleoliquefaction features. Seismological Research Letters, 88, 1403–1414.

Tuttle, M.P., Hartleb, R., Wolf, L. & Mayne, P.W. (2019) Paleoliquefaction studies and the evaluation of seismic hazard. Geosciences, 9, 311.

Üner, S. (2014) Seismogenic structures in Quaternary lacustrine deposits of Lake Van (eastern Turkey). Geologos, 20, 79–87.

Van Loon, A.J. & Maulik, P. (2011) Abraded sand volcanoes as a tool for recognizing paleo‐earthquakes, with examples from the Cisuralian Talchir Formation near Angul (Orissa, eastern India). Sedimentary Geology, 238, 145–155.

Van Rensbergen, P., Hillis, R.R., Maltman, A.J. & Morely, C.K. (2003) Subsurface sediment mobilization: introduction. In: Hillis, R.R., Maltman, A.J., Morely, C.K. & Van Rensbergen, P. (Eds.) Subsurface sediment mobilization, vol. 216. London: Geological Society Special Publication, pp. 1–8.

Villamor, P., Almond, P., Tuttle, M.P., Giona‐Bucci, M., Langridge, R.M., Clark, K., Ries, W., Bastin, S.H., Eger, A., Vandergoes, M., Quigley, M.C., Barker, P., Martin, F. & Howarth, J. (2016) Liquefaction features produced by the 2010–2011 Canterbury earthquake sequence in southwest Christchurch, New Zealand, and preliminary assessment of paleoliquefaction features. Bulletin of the Seismological Society of America, 106, 1747–1771.

Wheatley, D.F. & Chan, M.A. (2017) Water escape versus gas escape structures: examples from the ancient and modern records and laboratory experiments. Reservoir, 44(6), 14–21.

Williams, J.G. (1974) Sand boils: a modern analogue of ancient sand volcanoes. Journal of the Arkansas Academy of Science, 28, 80–81.