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Item 7.01 Regulation FD Disclosure. On February 27, 2013, Cloud Peak Energy Inc. Posted investor slides, dated February, 2013, on the Investor Relations section of www.cloudpeakenergy.com. These slides are furnished as Exhibit 99.1 to this Form 8-K and incorporated herein by reference. The Cloud Peak Energy website is not intended to function as a hyperlink, and the information contained on such website is not a part of this Form 8-K. Item 9.01 Financial Statements and Exhibits (d) Exhibits. The following exhibit is being furnished herewith. 99.1 Furnished February 2013 Investor Slides 2. 1 Cloud Peak Energy Inc.
Financial Data Cloud Peak Energy Inc. Is the sole owner of Cloud Peak Energy Resources LLC. Unless expressly stated otherwise in this presentation, all financial data included herein is consolidated financial data of Cloud Peak Energy Inc. Cautionary Note Regarding Forward-Looking Statements This presentation contains forward-looking statements within the meaning of the safe harbor provisions of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Forward-looking statements are not statements of historical facts, and often contain words such as may, will, expect, believe, anticipate, plan, estimate, seek, could, should, intend, potential, or words of similar meaning.
Forward-looking statements are based on managements current expectations, beliefs, assumptions and estimates regarding our company, industry, economic conditions, government regulations, energy policies and other factors. These statements are subject to significant risks, uncertainties and assumptions that are difficult to predict and could cause actual results to differ materially and adversely from those expressed or implied in the forward-looking statements. For a description of some of the risks and uncertainties that may adversely affect our future results, refer to the risk factors described from time to time in the reports and registration statements we file with the Securities and Exchange Commission, including those in Item 1A 'Risk Factors' of our most recent Form 10-K and any updates thereto in our Forms 10-Q and current reports on Forms 8-K.
There may be other risks and uncertainties that are not currently known to us or that we currently believe are not material. We make forward-looking statements based on currently available information, and we assume no obligation to, and expressly disclaim any obligation to, update or revise publicly any forward-looking statements made in our presentation, whether as a result of new information, future events or otherwise, except as required by law. Non-GAAP Financial Measures This presentation includes the non-GAAP financial measures of (1) Adjusted EBITDA (on a consolidated basis and for our reporting segments) and (2) Adjusted Earnings Per Share (Adjusted EPS). Adjusted EBITDA and Adjusted EPS are intended to provide additional information only and do not have any standard meaning prescribed by generally accepted accounting principles in the U.S.
A quantitative reconciliation of historical net income to Adjusted EBITDA and EPS (as defined below) to Adjusted EPS is found in the tables accompanying this presentation. EBITDA represents net income, or income from continuing operations, as applicable, before (1) interest income (expense) net, (2) income tax provision, (3) depreciation and depletion, (4) amortization, and (5) accretion. Adjusted EBITDA represents EBITDA as further adjusted to exclude specifically identified items that management believes do not directly reflect our core operations. The specifically identified items are the impacts, as applicable, of: (1) the updates to the tax agreement liability, including tax impacts of our 2009 initial public offering and 2010 secondary offering, (2) adjustments for derivative financial instruments including mark-to-market amounts and cash settlements realized, and (3) our significant broker contract that expired in the first quarter of 2010.
Because of the inherent uncertainty related to the items identified above, management does not believe it is able to provide a meaningful forecast of the comparable GAAP measures or a reconciliation to any forecasted GAAP measures. Adjusted EPS represents diluted earnings (loss) per common share attributable to controlling interest, or diluted earnings (loss) per common share attributable to controlling interest from continuing operations, as applicable (EPS), adjusted to exclude the estimated per share impact of the same specifically identified items used to calculate Adjusted EBITDA and described above, adjusted at the statutory rate of 36%. Adjusted EBITDA is an additional tool intended to assist our management in comparing our performance on a consistent basis for purposes of business decision-making by removing the impact of certain items that management believes do not directly reflect our core operations. Adjusted EBITDA is a metric intended to assist management in evaluating operating performance, comparing performance across periods, planning and forecasting future business operations and helping determine levels of operating and capital investments.
Period-to-period comparisons of Adjusted EBITDA are intended to help our management identify and assess additional trends potentially impacting our company that may not be shown solely by period-to-period comparisons of net income or income from continuing operations. Our chief operating decision maker uses Adjusted EBITDA as a measure of segment performance. Consolidated Adjusted EBITDA is also used as part of our incentive compensation program for our executive officers and others. We believe Adjusted EBITDA and Adjusted EPS are also useful to investors, analysts and other external users of our consolidated financial statements in evaluating our operating performance from period to period and comparing our performance to similar operating results of other relevant companies.
Adjusted EBITDA allows investors to measure a companys operating performance without regard to items such as interest expense, taxes, depreciation and depletion, amortization and accretion and other specifically identified items that are not considered to directly reflect our core operations. Similarly, we believe our use of Adjusted EPS provides an appropriate measure to use in assessing our performance across periods given that this measure provides an adjustment for certain specifically identified significant items that are not considered to directly reflect our core operations, the magnitude of which may vary drastically from period to period and, thereby, have a disproportionate effect on the earnings per share reported for a given period. Our management recognizes that using Adjusted EBITDA and Adjusted EPS as performance measures has inherent limitations as compared to net income, income from continuing operations, EPS or other GAAP financial measures, as these non-GAAP measures exclude certain items, including items that are recurring in nature, which may be meaningful to investors. Adjusted EBITDA and Adjusted EPS should not be considered in isolation and do not purport to be alternatives to net income, income from continuing operations, EPS or other GAAP financial measures as a measure of our operating performance. Because not all companies use identical calculations, our presentations of Adjusted EBITDA and Adjusted EPS may not be comparable to other similarly titled measures of other companies. Moreover, our presentation of Adjusted EBITDA is different than EBITDA as defined in our debt financing agreements.
2 Cloud Peak Energy Profile One of the largest U.S. Coal producers 2012 coal shipments from Owned and Operated Mines of 90.6 million tons 2012 proven & probable reserves of 1.3 billion tons Only pure-play PRB coal company Extensive NPRB base for long-term growth opportunities Employs approximately 1,700 people NYSE: CLD (2/13/13) $16.95 Market Capitalization (2/13/13) $1 billion Total Available Liquidity (12/31/12) $778 million 2012 Revenue $1.5 billion Senior Debt (B1/BB-) (12/31/12) $600 million Market and Financial Overview Company Overview. Crow Tribal Legislature Agreements 21 Overview and process Exploration Agreement and Option Agreement to lease up to 1.4 billion tons of in-place Northern PRB coal. Approved by the Legislature and signed by the Crow Tribe and Cloud Peak Energy in January 2013. Cloud Peak Energy paid the Crow Tribe $2.25 million upon the signing.
The executed agreements have been submitted to the U.S. Department of the Interior for up to 180 days for review and requested approval by the Bureau of Indian Affairs. On approval, further $1.5 million payment to the Crow Tribe.
Crow Tribal Legislature Agreements 22 Exploration Agreement To complete delineation of the potentially economic coal tonnages subject to the options. Option Agreement Three exclusive options to lease three separate coal deposits. Initial five-year term, with potential extensions through 2035 if certain conditions are met. Total option payments of up to $10 million over the initial term, with additional annual option payments through any extension periods. Option exercise payments equal to $0.08 to $0.15 per ton, variable by deposit.
25 Executing on our Export Strategy Strong International Demand Cloud Peak Energy Logistics Established as the Primary Exporter of PRB Coal Youngs Creek Asset Acquisition Crow Exploration and Option Agreements Secured Port Throughput China and India expected to continue to drive significant demand growth Other Asian countries seeking security and diversity of supply Australian and Indonesian supply being hit by increasing capital and operating costs and regulatory uncertainty U.S. 28 2013 Guidance Estimates and 2012 Actuals 2013 (estimated) 2012 (actual) Inclusive of intersegment sales Non-GAAP financial measure Excluding impact of Tax Receivable Agreement.
(4) Excluding capitalized interest and federal coal lease payments. Operating Segments 30 Owned and Operated Mines - mine site sales from our three owned and operated mines Key metrics: Tons sold Realized price per ton Cost of product sold per ton Logistics and Related Activities delivered sales from our logistics and transportation services to international and domestic customers Key profitability drivers: Tons delivered Cost of transportation services contracted Benchmark price of Newcastle for international deliveries Corporate and Other Broker activity Results from 50% interest in Decker mine Unallocated corporate costs.
Owned and Operated Mines 31 Our Owned and Operated Mines segment comprises the results of mine site sales from our three owned and operated mines primarily to our domestic utility customers and also to our Logistics and Related Activities segment. (in millions, except per ton amounts) Q4 2012 Q4 2011 Full Year 2012 Full Year 2011 Tons sold 23.6 25.2 90.6 95.6 Realized price per ton sold $13.07 $13.06 $13.19 $12.92 Average cost of product sold per ton $ 9.38 $ 9.15 $ 9.57 $ 9.12 Adjusted EBITDA (1) $ 75.4 $ 88.2 $283.3 $318.8 We reduced production in 2012 by 5 million tons in response to weaker market demand Managed costs well Reduced use of contractors Matching labor demands to market needs Conditionally monitoring and maintenance program for equipment (1) Reconciliation tables for Adjusted EBITDA are included in the Appendix.
Logistics and Related Activities 32 Our Logistics and Related Activities segment comprises the results of our logistics and transportation services to our domestic and international customers. Profitability improvements Higher Newcastle prices resulting in higher settlement to international customers Curtailed international deliveries through Ridley Terminal $11.2 million realized gain in derivative financial instruments (1) Reconciliation tables for Adjusted EBITDA are included in the Appendix (in millions) Q4 2012 Q4 2011 Full Year 2012 Full Year 2011 Tons delivered 1.3 1.3 5.8 5.9 Revenue $ 65.1 $ 72.3 $ 338.8 $ 327.4 Cost of product sold (delivered tons) $ 57.5 $ 66.2 $ 280.2 $ 294.2 Adjusted EBITDA (1) $ 15.4 $ 2.6 $ 57.1 $ 24.7. 36 Reconciliation of Non-GAAP Measures Adjusted EBITDA (in millions) (1) Changes to related deferred taxes are included in income tax expense.
38 Reconciliation of Non-GAAP Measures Adjusted EPS Three Months Ended December 31, Year Ended December 31, 2012 2011 2012 2011 Diluted earnings per common share $ 0.46 $ 0.72 $ 2.85 $ 3.13 Tax agreement expense (benefit) including tax impacts of IPO and Secondary Offering (0.58) (0.63) Derivative financial instruments 0.08 (0.02) (0.12) (0.02) Expired significant broker contract Adjusted EPS $ 0.54 $ 0.70 $ 2.15 $ 2.47 Weighted-average dilutive shares outstanding (in millions) 61.3 60.7 60.9 60.6. 44 Lease Acquisition Strategy Building Reserves Source: Cloud Peak Energy management. Note: Acquired tonnage is not classified as reserve until verified with sufficient technical and economic analysis. Maps not to scale. Cordero Rojo Mine (8425 Btu) Maysdorf II North Tract Maysdorf II LBA is expected to be bid 2013. Tonnages below are as estimated by the BLM. Maysdorf II North Tract 149 million minable tons (1) Maysdorf II South Tract - 234 million minable tons (1) (1) In October 2012, an environmental group filed a notice of appeal with the Interior Board of Land Appeals, challenging the Bureau of Land Managements record of decision authorizing the sale and issuance of the Maysdorf II North and South tracts.
Subsequently, the environmental group requested to dismiss the appeal, which was granted by the Board of Land Appeals. Additional legal challenges may be made in the future. WAII North and South Tracts 383 million proven and probable reserves(1) Ridgerunner lease previously acquired 81 million proven and probable reserves Extends mine life by approximately 12 years at current production rates (1) Environmental organizations challenged certain actions of the BLM and Secretary of the Interior relating to the North and South tract leases. On July 30, 2012, the U.S.
District Court for D.C. Rejected these challenges. In September 2012, the environmental organizations appealed the District Courts decision to the D.C. Court of Appeals. Any adverse outcome of the appeal could adversely impact or delay our ability to mine the coal subject to the leases. Antelope Mine (8875 Btu) Ridgerunner Lease South Tract Acquired 2011 North Tract Acquired 2011 AWARDED LBA Mined Area (2009/1010) Leased Coal Maysdorf II South Tract GRAPHIC 3 g60081mmi001.jpg GRAPHIC begin 644 g60081mmi001.jpg MCX``02D9)1@`!`0$`8`!@``#VP!#``@&!@KQ O/T?;W^/GZ 0`'P$``P$!`0$! M`0$!`0````````$'`P0%!@)/#%OJ=U%%'-(S@ MK%G;PQ'N1 #J+'QM8PP#'K!4!T'#CC `.VOA5R3^RP!^3T(TZU& M,(RMT:MZ-BI593E&9@RK7B2ZTSQ?HCQ0PM!J!?S'?YG.H:WXE 0 M)XR'A073W?,+CS+HL.,.K+/^2F^$/K)2G`)+.50T;J593T((Y%<% )&8&Z$$F'.D6(^V!
Abstract In volcanically and seismically active rift systems, preexisting faults may control the rise and eruption of magma, and direct the flow of hydrothermal fluids and gas in the subsurface. Using high-resolution airborne imagery, field observations, and CO 2 degassing data on Aluto, a typical young silicic volcano in the Main Ethiopian Rift, we explore how preexisting tectonic and volcanic structures control fluid pathways and spatial patterns of volcanism, hydrothermal alteration and degassing.
A new light detection and ranging (lidar) digital elevation model and evidence from deep geothermal wells show that the Aluto volcanic complex is dissected by rift-related extensional faults with throws of 50–100 m. Mapping of volcanic vent distributions reveals a structural control by either rift-aligned faults or an elliptical caldera ring fracture. Soil-gas CO 2 degassing surveys show elevated fluxes (100 g m –2 d –1) along major faults and volcanic structures, but significant variations in CO 2 flux along the fault zones reflect differences in near-surface permeability caused by changes in topography and surface lithology. The CO 2 emission from an active geothermal area adjacent to the major fault scarp of Aluto amounted to ∼60 t d –1; we estimate the total CO 2 emission from Aluto to be 250–500 t d –1. Preexisting volcanic and tectonic structures have played a key role in the development of the Aluto volcanic complex and continue to facilitate the expulsion of gases and geothermal fluids.
This case study emphasizes the importance of structural mapping on active rift volcanoes to understand the geothermal field as well as potential volcanic hazards. INTRODUCTION Existing fault structures can play a significant role in the development of a volcanic complex, ultimately providing high permeability pathways for magma, hydrothermal fluids, and gas to ascend to the surface (e.g.,;;; ). Understanding how preexisting structures such as regional tectonic faults and caldera ring faults affect fluid flow to the surface is a major task in defining the evolution of rift zones and has important implications for mineralization, geothermal exploration, and the assessment of volcanic hazard. Recent work, specifically focused on hydrothermal venting and volcanic degassing (; ), has shown that while preexisting structures may control permeability at the edifice scale, at smaller scales these structural controls may be obscured by localized near-surface permeability variations. These local influences may include (1) lithological variations, where fluids will preferentially migrate along high permeability layers (e.g., poorly consolidated tephra layers) and (2) topographic controls, where the stress field induced by gravitational loading causes fracturing parallel to topography, and focuses pathways for steam and other gases toward topographic highs.
To understand how large-scale structures influence active volcanic processes it is useful to look at the surface expression of different volcanic fluids (i.e., magma, hydrothermal fluids, and gas) across a variety of scales to disentangle large-scale structural controls from these localized near-surface permeability variations. Both direct and remote measurements can be used to assess the spatial distribution of fluids and fluid pathways. Remotely sensed data such as lidar (light detection and ranging) and aerial photography (e.g.,; ) are powerful tools to analyze volcano morphology, map sites of eruption and extrusion, and distinguish zones of hydrothermal alteration and fluid upwelling (e.g., ).
On the other hand, volcanic gases (e.g., CO 2) that may be difficult to detect remotely, can be readily measured in the field using modern surveying techniques and gridded to produce detailed maps of gas flux across a volcanic edifice (; ). These techniques allow us to build detailed pictures of how different fluids are released from active volcanoes; the challenge for volcanologists is integrating these observations to unravel the subsurface structure and the processes controlling fluid pathways. The Main Ethiopian Rift (MER, East Africa) provides an ideal natural laboratory to study how preexisting structural features (of both volcanic and tectonic origin) influence active volcanic processes.
Firstly, the MER hosts a number of young silicic peralkaline volcanoes, allowing investigation of active magmatic and geothermal systems. Secondly, extension in the MER has generated abundant faults and fracture networks (e.g.,; ) through which magma can ascend and erupt. Finally, many of the MER volcanoes have undergone caldera collapse and thus are likely to have established ring fault systems (;;;; ). The silicic peralkaline volcanoes of the MER are among the least studied on Earth: few have detailed geological maps and significant knowledge gaps exist regarding their past and current activity. Detailed studies of peralkaline volcanic systems are limited to a few key complexes (e.g., Pantelleria;,;;;; ), despite the fact that they appear to be a ubiquitous feature of continental rift zones (; ). The caldera structures produced at peralkaline volcanic centers in the East African Rift system are also of note because many appear elliptical in map view (e.g.,;; ).
While several recent publications have emphasized the role of elongate magma chamber collapse in generating elliptical calderas in the East African Rift system (e.g.,; ), there is a lack of consensus regarding the exact mechanism in the MER. Establishing the controls on magma rise and ponding in tectonically thinned crust is fundamental to understanding how continental rift zones evolve. In this paper we integrate observations from field campaigns, airborne remote sensing (lidar, aerial photos) and soil-gas CO 2 surveys to examine how magma, hydrothermal fluid, and gas pathways are coupled to the major structural features on Aluto, a typical young peralkaline volcanic complex of the MER. We show that each data set provides unique information about the complex and the links between volcanic activity and preexisting volcanic and tectonic structures.
From these data we develop a conceptual model that captures both the volcanic evolution and the role these major structures play in controlling fluid pathways. MER—REGIONAL SETTING The MER is a zone of active extension in the East African Rift system that connects the Afar depression to the north with the Turkana depression and Kenyan rift to the south.
The MER is an oblique rift, exhibiting an overall NE–SW trend, formed by E–W extension between the Nubia and Somalia plates via both magmatic intrusion and tectonic faulting (;; ). Geodetic and seismic data (;; ) indicate that the current E–W (∼N100°E) extension rates are 4–6 mm yr –1. The MER is usually divided into three sectors (northern, central, and southern) that reflect differences in terms of the spatial pattern of the faulting , the timing of the major faulting episodes (;; ), and the thermal-mechanical state of the lithosphere (e.g., ).
This pattern is consistent with rift maturity increasing northward along the MER toward Afar, where the overall physiology changes from continental rifting to incipient oceanic spreading (;; ). The MER has two distinct fault sets: (1) NE–SW-oriented border faults with large vertical offsets (100 m) on the boundaries of the rift, and (2) a set of closely spaced internal faults, the Wonji faults, with smaller vertical offsets (10 m 2, which can be mapped using aerial photographs. While an automated mapping approach using the spectral signature of these alteration facies (e.g., ) would be feasible given our data set, for the purposes of this study the resolution of the aerial photos is sufficiently high that major altered zones can be approximately mapped, and their locations can be linked with structural interpretations and CO 2 degassing results. Our assessment of hydrothermal alteration made using the orthophotos correlates well with fumarole vents mapped on the ground by the Geological Survey of Ethiopia ; for hot spring locations that were beyond the coverage of our remote sensing data, we used to constrain their location. Soil CO 2 Flux Measurements of soil CO 2 flux on Aluto were undertaken in three surveys between January 2012 and February 2014. The first survey (January 2012) sought to transect large-scale structures and identify whether they provided key permeability pathways for CO 2-rich geothermal fluids and magmatic gases to upwell.
Degassing surveys were conducted in November 2012 and February 2014, and focused on producing a detailed map of spatial degassing patterns along the major tectonic fault (Artu Jawe fault zone). A 1000 m × 800 m study area was chosen to include both the major fault scarp (photograph in ) and the productive geothermal wells (LA-3 and LA-6). A 30-m sampling grid was use, a compromise between attaining spatial coverage of the fault zone at sufficient sampling resolution.
In total 560 sites were visited (424 in November 2012 and 136 in February 2014). Those that were in geothermal effluent ponds, areas of dense vegetation, or on hazardous slopes were excluded, and in some instances extra measurements were made off the predefined sampling grid to help characterize the highest values in the degassing regions. The CO 2 flux was measured directly using two portable closed system gas analyzer units (a LICOR LI-8100 automated soil CO 2 flux system and a PP-systems SRC-1 chamber with EGM-4 analyzer). Both instruments have an infrared gas analyzer and use the accumulation method (; ) to measure CO 2 flux. Measurements were consistent between the instruments; comparisons made at identical sites showed variations of 10%–25% between the two instruments (significantly less than the variation seen across the complex). Repeated site measurements showed variations of ∼25% in low flux zones (100 g m –2 d –1), consistent with random error in natural emission rates (; ) and in line with the quoted reproducibility of each instrument (5%–10%,; ). To generate maps of soil CO 2 flux from the discrete point measurements the sequential Gaussian simulation (sGs) method was used.
A simulation grid was defined (at higher spatial resolution than the sampling grid) and 100 sGs were performed using the sgsim code available in the Stanford Geostatistical Modeling Software (SGeMS) open-source geostatistics package. A CO 2 flux map was constructed from these simulations taking the arithmetic mean of each individual cell across all simulations, equivalent to the E-type soil flux map proposed. The total CO 2 flux was calculated for each simulation and the mean and standard deviations of all simulations were computed and used to estimate total CO 2 release as well as the associated uncertainty. RESULTS Recent Volcanism and Links to a Ring Fracture System The spatial distribution of volcanic vents on Aluto is shown in. Vents are largely restricted to the main edifice and a NNE–SSE-trending zone to the northwest of this.
A detailed map of volcanic vents, lava flows, craters and fissures overlain on the lidar DEM is given in. Lava flows on the central edifice are rhyolitic; shows shaded relief and slope maps for a typical obsidian lava deposit. Craters are predominantly 10,000 g m –2 d –1 (the full range of flux values along the fault zone is shown in ). Profile B–B′ transects the remnant caldera rim structure. The CO 2 flux shows greatest values (to 1850 g m –2 d –1) at the base of the caldera rim, with lower values (2–7 g m –2 d –1) to the southwest and on the caldera rim.
The area of anomalous degassing is defined by several sets of fumaroles; CO 2 flux values are greatest on fumaroles (500–1850 g m –2 d –1) and lower in cohesive soils between the open fractures (15–240 g m –2 d –1; ). Profile C–C′ follows the topographic high on the southern rim of the complex. The CO 2 flux values increase from low background values (50–60 m in height) is comparable to other peralkaline calderas where subsidence is a few hundred meters.
The elliptical caldera form is typical of continental rift volcanoes worldwide (e.g.,;;;; ). Elliptical calderas may be produced by a number of different mechanisms , including (1) collapse of an elliptical magma reservoir; (2) nesting, where multiple collapse structures overlap and give rise to an elongate geometry; (3) shallow crustal processes, where asymmetric collapse, or distortion of caldera faults leads to an asymmetric caldera above a circular magma chamber; and (4) post-caldera modification, where a circular caldera is distorted by erosion or regional deformation. Ultimately, the infilling of the Aluto caldera has left little information concerning the original collapse structure and the nature of the collapse event. In particular, it is unclear whether the caldera collapse involved one or multiple events, to create a nested structure (as is typical for peralkaline volcanic complexes;;; ).
It is also not possible to infer whether collapse was asymmetric or whether subsidence was accommodated by existing tectonic faults. Assuming that collapse took place at 155 ka, the only age constraint for the major ignimbrite deposits of Aluto , and assuming current extension rates of 5 mm yr –1 (; ), then this would generate 90% of the water in the Aluto geothermal system is derived from rainfall from the rift shoulders with a minimal component (. Topographic map of the Main Ethiopian Rift (MER) indicating the three main sectors (northern, central and southern, i.e., NMER, CMER, and SMER). The surface faults (mapped by ) are shown in blue. Earthquake locations and focal mechanisms for the region are from the Global Centroid Moment Tensor Project catalogue (; 1976–2012; M 5). Red triangles identify volcanic centers thought to have been active in the Holocene.
White stars identify major centers of population (after the Socioeconomic Data and Applications Center, ): AA—Addis Ababa; NZ—Nazareth; SH—Shashemene; AW—Awassa. Lakes outlined in the MER: Ko—Lake Koka; Zw—Lake Ziway; Ln—Lake Langano; Ab—Lake Abijta; Sh—Lake Shala; Aw—Lake Awasa; Ay—Lake Abaya.
The Aluto volcanic complex is located within the white rectangle. Topographic map of the Main Ethiopian Rift (MER) indicating the three main sectors (northern, central and southern, i.e., NMER, CMER, and SMER). The surface faults (mapped by ) are shown in blue.
Earthquake locations and focal mechanisms for the region are from the Global Centroid Moment Tensor Project catalogue (; 1976–2012; M 5). Red triangles identify volcanic centers thought to have been active in the Holocene.
White stars identify major centers of population (after the Socioeconomic Data and Applications Center, ): AA—Addis Ababa; NZ—Nazareth; SH—Shashemene; AW—Awassa. Lakes outlined in the MER: Ko—Lake Koka; Zw—Lake Ziway; Ln—Lake Langano; Ab—Lake Abijta; Sh—Lake Shala; Aw—Lake Awasa; Ay—Lake Abaya. The Aluto volcanic complex is located within the white rectangle.
(A) ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) RGB321 image of Aluto volcano and the surrounding area. Geothermal wells on Aluto are labeled in blue (only wells LA-3 and LA-6 are productive). Yellow lines indicate the location of faults mapped in previous studies (; ) or indicated by deep well data (in B). Black open arrowheads or view lines indicate viewing direction for photographs in.
Coordinates are in UTM (Universal Transverse Mercator) Zone 37N, with the WGS84 (World Geodetic System 1984) datum (for this figure as well as all subsequent maps). AJFZ—Artu Jawe fault zone; RTS—regional tectonic structures visible east of Aluto; CR—caldera rim. (B) West-east cross section showing the deep stratigraphy and hypothesized subsurface structure. Well data represent the synthesis of several publications (;; ) and drilling reports provided by the Geological Survey of Ethiopia (;;; ). The geological units shown have been correlated between the different wells on Aluto (; ) and indicate a prevailing mode of deposition rather than a single homogeneous unit (e.g., paleosols occur within the Bofa basalt and ash horizons occur within lacustrine sequences). The section line is shown in A.
Note also that data from well LA-5 have been collapsed onto the section line. (A) ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) RGB321 image of Aluto volcano and the surrounding area. Geothermal wells on Aluto are labeled in blue (only wells LA-3 and LA-6 are productive). Yellow lines indicate the location of faults mapped in previous studies (; ) or indicated by deep well data (in B).
Black open arrowheads or view lines indicate viewing direction for photographs in. Coordinates are in UTM (Universal Transverse Mercator) Zone 37N, with the WGS84 (World Geodetic System 1984) datum (for this figure as well as all subsequent maps). AJFZ—Artu Jawe fault zone; RTS—regional tectonic structures visible east of Aluto; CR—caldera rim. (B) West-east cross section showing the deep stratigraphy and hypothesized subsurface structure. Well data represent the synthesis of several publications (;; ) and drilling reports provided by the Geological Survey of Ethiopia (;;; ). The geological units shown have been correlated between the different wells on Aluto (; ) and indicate a prevailing mode of deposition rather than a single homogeneous unit (e.g., paleosols occur within the Bofa basalt and ash horizons occur within lacustrine sequences).
The section line is shown in A. Note also that data from well LA-5 have been collapsed onto the section line. Photographs of major volcanic and tectonic structures on Aluto. (A) The Artu Jawe fault scarp viewed from the west (located in ).
Along the escarpment fumaroles are visible at the base of the structure and there is evidence of hydrothermal alteration at the surface. (B) Subvertical foliations developed in obsidian in crush zone of Artu Jawe fault scarp (located in A). Hammer is 30 cm in length. (C) The caldera wall of Aluto, identifying fumarole vents (red circles) and hydrothermal alteration at the base of the structure.
Asterisk in the center of the fumarole field indicates a zone that does not show any surface alteration and has low ground temperatures and CO 2 gas flux relative to the surroundings (see text). Photographs of major volcanic and tectonic structures on Aluto. (A) The Artu Jawe fault scarp viewed from the west (located in ).
Along the escarpment fumaroles are visible at the base of the structure and there is evidence of hydrothermal alteration at the surface. (B) Subvertical foliations developed in obsidian in crush zone of Artu Jawe fault scarp (located in A). Hammer is 30 cm in length.
(C) The caldera wall of Aluto, identifying fumarole vents (red circles) and hydrothermal alteration at the base of the structure. Asterisk in the center of the fumarole field indicates a zone that does not show any surface alteration and has low ground temperatures and CO 2 gas flux relative to the surroundings (see text). Map of volcanic vents, hydrothermal alteration, active fumaroles, and hot springs in the Aluto volcanic complex. Faults on the complex have either been mapped using remote sensing data sets (this study) or have been suggested by previous geological mapping reports and deep well data (;;; ). Regional faults were mapped. The dashed ellipses show the size and orientation of a buried ring fault that we propose may explain the distribution of volcanic vents on the main edifice; the fine dashed ellipses represent ±500 m uncertainty bounds on the central ellipse. The mapped caldera rim overlaps the proposed ring structure.
Major hydrothermal zones are labeled and link to the summary in, where the abbreviations used in the figure are expanded. Map of volcanic vents, hydrothermal alteration, active fumaroles, and hot springs in the Aluto volcanic complex.
Faults on the complex have either been mapped using remote sensing data sets (this study) or have been suggested by previous geological mapping reports and deep well data (;;; ). Regional faults were mapped. The dashed ellipses show the size and orientation of a buried ring fault that we propose may explain the distribution of volcanic vents on the main edifice; the fine dashed ellipses represent ±500 m uncertainty bounds on the central ellipse.
The mapped caldera rim overlaps the proposed ring structure. Major hydrothermal zones are labeled and link to the summary in, where the abbreviations used in the figure are expanded. (A) Lidar hillshade DEM covering the main edifice of Aluto volcano (black box in ).
Black box insets link to and, where detailed imagery and interpretation of the volcanic features are given. Black triangular features show the viewing direction for the three-dimensional DEM imagery given in. The light blue lines A–A′, B–B′, and C–C′ correspond to the CO 2 degassing transects given in. (B) Structural map and interpretation of the DEM imagery. The older, more weathered obsidian lava flows of Aluto are covered in a thin shower of gray pumice, unlike the younger obsidian lavas. The lidar data set used in this study is. (A) Lidar hillshade DEM covering the main edifice of Aluto volcano (black box in ).
Black box insets link to and, where detailed imagery and interpretation of the volcanic features are given. Black triangular features show the viewing direction for the three-dimensional DEM imagery given in. The light blue lines A–A′, B–B′, and C–C′ correspond to the CO 2 degassing transects given in. (B) Structural map and interpretation of the DEM imagery. The older, more weathered obsidian lava flows of Aluto are covered in a thin shower of gray pumice, unlike the younger obsidian lavas. The lidar data set used in this study is.
Examples of volcanic features mapped using the airborne data sets. (A) Hillshade DEM and slope map showing a typical obsidian lava flow vent and elongate crater.
These flows often preserve compression folds on the surface that are characteristic of viscous silicic lavas (e.g.,;; ). The length-weighted rose diagram (top right) was generated by analyzing the orientation of all the individual segments that compose the crater feature (yellow outline); the dominant ESE–WNW orientation is clearly identified (for a circular crater rim, a radial distribution would be generated). (B) Aerial photograph of the Auto fumarole zone on the west of Aluto. Hydrothermal alteration of pumiceous deposits produces bright red clays adjacent to active fumaroles. (C) Hillshade DEM identifying a set of three aligned obsidian domes and nested craters on the west of the caldera floor suggestive of an underlying tectonic control.
Examples of volcanic features mapped using the airborne data sets. (A) Hillshade DEM and slope map showing a typical obsidian lava flow vent and elongate crater.
These flows often preserve compression folds on the surface that are characteristic of viscous silicic lavas (e.g.,;; ). The length-weighted rose diagram (top right) was generated by analyzing the orientation of all the individual segments that compose the crater feature (yellow outline); the dominant ESE–WNW orientation is clearly identified (for a circular crater rim, a radial distribution would be generated).
(B) Aerial photograph of the Auto fumarole zone on the west of Aluto. Hydrothermal alteration of pumiceous deposits produces bright red clays adjacent to active fumaroles. (C) Hillshade DEM identifying a set of three aligned obsidian domes and nested craters on the west of the caldera floor suggestive of an underlying tectonic control. Three-dimensional view of the hillshade DEM covering the Artu Jawe fault zone. (A) Fault scarps and their possible continuation into the volcanic pile (indicated by deep gorges); geothermal wells are also shown (the only productive wells are located adjacent to the major fault scarp). (B) Fumaroles identified either in the field or using locations reported from field mapping by the Geological Survey of Ethiopia.
The pink shaded area and dashed line delimit the pumice dome ; the elongate nature of the dome is interpreted to reflect the underlying tectonic control. Three-dimensional view of the hillshade DEM covering the Artu Jawe fault zone. (A) Fault scarps and their possible continuation into the volcanic pile (indicated by deep gorges); geothermal wells are also shown (the only productive wells are located adjacent to the major fault scarp). (B) Fumaroles identified either in the field or using locations reported from field mapping by the Geological Survey of Ethiopia. The pink shaded area and dashed line delimit the pumice dome ; the elongate nature of the dome is interpreted to reflect the underlying tectonic control. Rose plots comparing regional fault trends, volcanic crater rim and fissure orientation and vent alignments, shown as trends in degrees from north (i.e., 0° = north; 90° = east; 180° = south). Arrows are used to identify the long and short axis of the ring structure (white), which has an approximately E–W elongation; the mean trend of the Wonji faults (red); and the mean trend of the border faults (gray).
(A, B) Regional fault strike for the Wonji and border faults of the central Main Ethiopian Rift analyzed using the database (available online at ). (C) Length-weighted rose plot that analyzes the orientation of all crater rim and fissure line segments mapped using the lidar data set (shown in ) to identify prevailing orientations of elongate vents and fissure features. (D, E) The azimuth between neighboring volcanic vents, analyzed using the vent locations (black point features) in. Vent azimuth is analyzed both on and off the main edifice (i.e., the area covered by the lidar; ). The data are filtered such that only those vents separated by 0.2–2 km are analyzed.
A number of different distance filter windows were explored and while the 0.2–2 km filter window is shown here, the results of similar size windowing methods between 0.1 km and 4 km tended to produce comparable results. Rose plots comparing regional fault trends, volcanic crater rim and fissure orientation and vent alignments, shown as trends in degrees from north (i.e., 0° = north; 90° = east; 180° = south). Arrows are used to identify the long and short axis of the ring structure (white), which has an approximately E–W elongation; the mean trend of the Wonji faults (red); and the mean trend of the border faults (gray). (A, B) Regional fault strike for the Wonji and border faults of the central Main Ethiopian Rift analyzed using the database (available online at ).
(C) Length-weighted rose plot that analyzes the orientation of all crater rim and fissure line segments mapped using the lidar data set (shown in ) to identify prevailing orientations of elongate vents and fissure features. (D, E) The azimuth between neighboring volcanic vents, analyzed using the vent locations (black point features) in. Vent azimuth is analyzed both on and off the main edifice (i.e., the area covered by the lidar; ). The data are filtered such that only those vents separated by 0.2–2 km are analyzed.
A number of different distance filter windows were explored and while the 0.2–2 km filter window is shown here, the results of similar size windowing methods between 0.1 km and 4 km tended to produce comparable results. Focused study of degassing along the Artu Jawe fault zone. (A) Shaded relief digital elevation model (DEM) showing the Artu Jawe fault scarp (black) and its projected continuation north (dashed).
Less-pronounced breaks in topography (10–20 m high) west of the main fault scarp are marked by white dashed lines (these are also visible in in ). Blue points identify the location of the productive geothermal wells (LA-3 and LA-6), as well as the site of the new well (LA-9); pp—the Aluto-Langano geothermal power plant. (B) Surface geology map constructed from the observations of the exposure noted at each grid locality and further discriminated using the aerial photos.
Surface geology consists of pyroclastic deposits (pink), alluvium (yellow), and obsidian lava (red). (C) CO 2 flux map derived using the sequential Gaussian simulation (sGs) approach. Gray points represent a discrete flux measurement. W–W′, X–X′, Y–Y′, and Z–Z′ are transects in.
(D) Probability plot of soil CO 2 flux values from the survey grid identifying background and volcanic-hydrothermal populations in the distribution (for detailed explanation of application of probability plots to CO 2 flux data sets, see ). Focused study of degassing along the Artu Jawe fault zone. (A) Shaded relief digital elevation model (DEM) showing the Artu Jawe fault scarp (black) and its projected continuation north (dashed). Less-pronounced breaks in topography (10–20 m high) west of the main fault scarp are marked by white dashed lines (these are also visible in in ). Blue points identify the location of the productive geothermal wells (LA-3 and LA-6), as well as the site of the new well (LA-9); pp—the Aluto-Langano geothermal power plant.
(B) Surface geology map constructed from the observations of the exposure noted at each grid locality and further discriminated using the aerial photos. Surface geology consists of pyroclastic deposits (pink), alluvium (yellow), and obsidian lava (red). (C) CO 2 flux map derived using the sequential Gaussian simulation (sGs) approach. Gray points represent a discrete flux measurement. W–W′, X–X′, Y–Y′, and Z–Z′ are transects in. (D) Probability plot of soil CO 2 flux values from the survey grid identifying background and volcanic-hydrothermal populations in the distribution (for detailed explanation of application of probability plots to CO 2 flux data sets, see ). Conceptual model summarizing the evolution of the major structures on Aluto and their controls on surface volcanism, geothermal fluids, and degassing.
(A) Regional tectonic structures aligned with the Wonji faults develop prior to surface volcanism, creating fault-bounded blocks over which abrupt lateral thickness variations in the deep well lacustrine sediments occur. (B) Surface volcanism at Aluto builds a silicic shield, which then undergoes caldera collapse. The dynamics of caldera formation remain unclear, because most of the structure has either been removed by erosion or buried by subsequent volcanic deposits. (C) Post-caldera volcanic eruptions, as well as ongoing geothermal activity and degassing processes, exploit the existing volcanic and tectonic fault network. While various fault structures provide high permeability zones for fluid flow (, B–B′), the Artu Jawe fault zone appears to represent the main pathway connecting the hydrothermal reservoir to the surface.
Conceptual model summarizing the evolution of the major structures on Aluto and their controls on surface volcanism, geothermal fluids, and degassing. (A) Regional tectonic structures aligned with the Wonji faults develop prior to surface volcanism, creating fault-bounded blocks over which abrupt lateral thickness variations in the deep well lacustrine sediments occur. (B) Surface volcanism at Aluto builds a silicic shield, which then undergoes caldera collapse. The dynamics of caldera formation remain unclear, because most of the structure has either been removed by erosion or buried by subsequent volcanic deposits. (C) Post-caldera volcanic eruptions, as well as ongoing geothermal activity and degassing processes, exploit the existing volcanic and tectonic fault network. While various fault structures provide high permeability zones for fluid flow (, B–B′), the Artu Jawe fault zone appears to represent the main pathway connecting the hydrothermal reservoir to the surface.