Visualization of folding in marble outcrops, Connemara, western Ireland: An application of virtual outcrop technology

K.J.W. McCaffrey* Earth Sciences Department, Durham University, Durham, DH1 3LE, UK M. Feely R. Hennessy Department of Earth and Ocean Sciences, National University of Ireland, Galway, Ireland J. Thompson Earth Sciences Department, Durham University, Durham, DH1 3LE, UK

ABSTRACT al., 2000; Pringle et al., 2004a, 2004b; Clegg et a 3D representation of a landscape, such as a al., 2005; Trinks et al., 2006) or Digital Outcrop digital elevation model (DEM), enables students Virtual outcrops have been generated from Model (Bellian et al., 2005). Terrestrial laser to attain an improved perception of the geology terrestrial laser scanner data captured at two scanning (ground-based lidar [light detection in a particular region. These data sets also offer marble outcrops in the Dalradian rocks of and ranging]) is the most commonly used tool geoscientists the opportunity to collect quantita- Connemara, western Ireland. Both locations to generate these models. A laser pulse is emit- tive data sets and make observations from rock are popular fi eld study sites in the region, ted toward the outcrop, and the travel time of the exposures at their convenience, in contrast to where complex fold structures are visible refl ected light is used to calculate the distance collecting data during a time-pressured visit to in the outcrops. The development of virtual and three-dimensional (3D) coordinates of the the outcrop during fi eldwork. outcrops for student instruction is discussed, refl ecting point. In modern terrestrial laser scan- In this contribution, we provide two examples both in communicating the theories of struc- ners, this process is repeated up to 12,000 times to illustrate the role virtual outcrops can play in tural geology in the classroom, and in pre- and per second to build a high-resolution topographic education for undergraduate students and the post-fi eld study instruction. Supplementary model of the outcrop. Georeferencing the data general public. From terrestrial laser scanned VRML (Virtual Reality Modeling Language) set using a differential global positioning system data, we generated virtual outcrops for two clas- models, Google Earth KML (Keyhole Markup (GPS) permits the generation of a geospatially sic exposures of folded Neoproterozoic marbles Language) fi les, and movies are used to com- accurate virtual outcrop that contains fully inte- in Connemara, Ireland. The locations differ municate the associated geological context for grated supplementary geospatial data such as signifi cantly in outcrop architecture: one is a each locality. Virtual outcrops and associated maps, aerial photographs, and other data sets. marble quarry with cleanly cut vertical walls; three-dimensional (3D) geological visualiza- Virtual outcrop data sets are increasingly used the other is a geomorphologically irregular, tions have the potential to supplement tra- as a research tool in the earth sciences to investi- naturally eroded valley exposing marble. The ditional educational content and aid in the gate problems in geomorphology (Rosser et al., models generated were used in two training improvement of students’ visual literacy. 2005; Wawrzyniec et al., 2007), sedimentology exercises for undergraduate students. A virtual (Bellian et al., 2005; Redfern et al., 2007), struc- outcrop created for a small marble quarry was Keywords: folds, virtual outcrop, laser scan, tural geology (Trinks et al., 2005; Pearce et al., used by an undergraduate student who had not education, Ireland. 2006; Sagy et al., 2007), and hydrocarbon reser- visited the outcrops as a basis for a laboratory- voir engineering (Pringle et al., 2004b; Enge et based research dissertation. The student carried INTRODUCTION al., 2007). These methods are of signifi cance to out a detailed structural analysis of the fold archiving sites of geological importance where geometries and styles. The other virtual outcrop Advances in geospatial surveying technolo- access to fi eld sites is limited or restricted (e.g., model was used in an educational resource for gies have provided new methods for collect- Bates et al., 2008). students prior to their visit to the site. The laser ing outcrop data, and when supported by digi- The generation and use of virtual outcrops in scan data were integrated with a 3D Virtual tal photogrammetry, can render quantitatively the analysis and interpretation of geological out- Reality Modeling Language (VRML) model accurate and visually impressive representations crops can be extended to the classroom, where depicting the surface cover and bedrock geol- of geological outcrops (McCaffrey et al., 2005). high-quality 3D visualizations can serve as ogy. These models allow user-controlled multi- This approach produces a data set that has been excellent instruction tools for educators (Trinks perspective viewing of the region’s topography termed a Virtual Outcrop (Xu et al., 1999; Xu et et al., 2005). Embedding virtual outcrops within and associated geology at a variety of scales.

*[email protected]

Geosphere; June 2008; v. 4; no. 3; p. 588–599; doi: 10.1130/GES00147.1; 9 fi gures; 2 animations.

588 For permission to copy, contact [email protected] © 2008 Geological Society of America Fold visualization using virtual outcrops

Here we introduce the virtual outcrops, outline limestone, with intermittent sandstone beds and al., 1991; Tanner et al., 1989) and interpreted the methods used in their creation, and discuss abundant basic sills and lavas, and tuffaceous to have been emplaced from the northwest. The their application as an educational resource. horizons. The marbles of the Lakes Marble For- position of the Connemara Metamorphic Com- mation are mineralogically distinguished from plex is anomalous because it lies to the south of THE DALRADIAN MARBLES OF those of the Connemara Marble Formation by the Highland Boundary Fault. Elsewhere in Ire- CONNEMARA the lack of ophicalcite and dolomite, and visu- land and Scotland, Dalradian lithologies occur ally by their distinct blue-gray, ribbed appear- on the northwestern side of this major crustal Two distinct marble formations have been ance. The almost pure-calcite (and slightly discontinuity. The Dalradian Supergroup was described in the Neoproterozoic Dalradian rocks graphitic) marbles of the Lakes Marble Forma- deposited at the leading edge of Laurentia in Connemara (Leake and Tanner, 1994). These tion are generally homogenous but banded on a and is now exposed throughout the northwest- are the Lower Dalradian (Appin), Connemara centimeter scale, displaying thin ribs weathering ern parts of the British Isles. The sequence Marble Formation, and the Middle Dalradian out on the surface. was deformed and metamorphosed during the (Argyll) Lakes Marble Formation. Correlations Grampian (Taconic) orogeny resulting in the between the Connemara Dalradian and Scot- GEOLOGICAL SETTING OF THIS development in the Connemara region of four tish Dalradian have been described in Leake STUDY main fold phases and local attenuation of the and Tanner (1994). The Connemara Marble stratigraphic package. The metamorphic rocks Formation consists of green and white marbles, Two sites were identifi ed as excellent can- of Connemara have been subjected to amphibo- calcareous schists, and tremolitic amphibole- didates for widely useful virtual outcrops. The lite facies metamorphism, with grade increas- bearing rocks (Leake and Tanner, 1994). The sites are located 28 km apart on opposite sides ing from north (garnet zone) to south (upper Connemara Marbles have been correlated with of the ENE-WSW–trending Connemara Anti- sillimanite zone) through a series of east-west– the Scottish Appin Islay Limestone Formation form (Leake and Tanner, 1994) in the Neopro- trending metamorphic zones. (Leake and Tanner, 1994), and the rocks of terozoic-age Dalradian Metamorphic Complex the Argyll Lakes Marble Formation have been in Connemara, western Ireland (Fig. 1). The Streamstown Marble Quarry correlated with the Easdale Subgroup of the Connemara Dalradian, consisting of mainly Scottish Dalradian (Harris and Pitcher, 1975). marbles, schist, and quartzite, is allochthonous The two locations were chosen due to the The Lakes Marble Formation is a thick calcitic (Friedrich et al., 1999; Harris, 1995; Graham et contrasting nature of the exposures—one a

Figure 1. Geology of Connemara, Ireland, showing the locations of the two fi eld sites discussed in this paper.

Geosphere, June 2008 589 McCaffrey et al. natural outcrop surface and the other a quarry “z” fold patterns, with two distinct synformal estimate is given by the manufacturer as ±5 mm exposure. The fi rst location is a small quarry folds present on this west-facing outcrop. at these scales of observation (<25 m). at Streamstown (Irish National Grid 65497 261915) located 3 km northeast of Clifden in LIDAR DATA COLLECTION (LASER Data Acquisition: Cur Hill Connemara, western Ireland. It was chosen for SCANNING) its excellent exposures of Connemara Marble Four laser scans (three panoramas and one fold structures (see Fig. 2.26, p. 53, in Stan- The lidar data sets were collected from tripod detailed fi ne scan) were taken at Cur Hill from ley, 1999). The quarry is located in a pocket of positions that were sited for optimum view- three positions (Fig. 2B). Scans 1 and 3 were Connemara Marble, ~1 km east of the Renvyle- shed of the outcrops under study. Point clouds taken in the middle of the Green Valley, while Clifden-Murvey Fault, a major NNW-SSE struc- were captured over a two-day period with one scan 2 was taken approximately 4 m west of the tural feature traversing the western Connemara day spent at each location. A Riegl LMS Z420i iconic fold outcrop. Each panorama scan took region (Fig. 2A). Connemara Marble is found in laser scanner with typical acquisition rates up 4 min and 8 s to capture ~2 million measure- discontinuous outcrops stretching for ~30 km to 12,000 points/s was used (Fig. 3B). A Nikon ments at a laser rate of 24,100 Hz. The fi ne scan on the southern limb of the regionally signifi - D100 digital camera with a 14-mm lens was (145° horizontal sweep) took 10 min to capture cant D4 Connemara Antiform. At Streamstown, precisely mounted on the scanner and from pho- ~3.3 million readings at the same laser rate. the distribution of the Connemara Marble types tographs of the target area, provided individual is controlled by two mesoscale antiforms named color (RGB) attributes for the x,y,z point cloud. Point-Cloud Processing the Quarry and Crag antiforms (Fig. 2A). There A laptop, running RiSCAN Pro version 1.2.1 are three principal marbles in the quarry—a was used in the fi eld to control the scanner and After data were acquired, a series of standard white calcite marble, a green tremolite marble, camera, as well as for data storage and quality processing steps including scan co-registration and a green serpentine marble; hence struc- control of data gathering during the acquisition and georeferencing were followed to produce tures are well defi ned by the color contrasts. At process. a 3D model. A key challenge in processing Streamstown, the stone was extracted by sawing Ten scanner refl ectors (5-cm cylinder) were and analyzing laser scan data is to reduce fi le large blocks from the walls and fl oor resulting distributed around the study sites. The positions size without losing desired resolution because in smooth vertical and horizontal surfaces in the of these refl ectors were georeferenced using merged point-cloud fi les containing tens of mil- main quarry that provide an opportunity to test an Ashtech ProMark2 Differential GPS survey lions of points quickly overwhelm most personal our ability to extract useful 3D information from system. A base station (Fig. 3C) was set up to computers (PCs). For example, manual fi ltering a virtual data set (Fig. 5). record GPS data continuously, while fi ve other can remove extraneous returns from the veg- refl ector locations were captured using a rover etation in front of the outcrop surface and other Cur Hill, Maam Valley GPS unit. Postprocessing the GPS data resulted data that are peripheral to the main objective. in horizontal and vertical accuracies in the When viewed from a distance, the colored The second site chosen for the study is on the <2-cm range and enabled the point clouds to point cloud provides a reasonable representa- southern slopes of Cur Hill (93117 252856) in be co-registered with one another and georef- tion of the outcrop surface; however, on closer a major east-west–trending glacial valley, the erenced to the Irish National Grid. The internal inspection, as the data are zoomed toward the Maam Valley (see Yardley and Long, 1983). precision for the scan co-registration calculated viewer, the particulate nature of the point cloud Cur Hill (310 m) is located on the northern from the refl ector positions was less than 2 cm means that details of the structures become limb of the Connemara Antiform (Fig. 1), and in all three (x,y,z) directions. fuzzy (Fig. 4A). To overcome this effect, the consists of east-west–striking Middle Dalra- point clouds are meshed and the digital pho- dian marbles, metasediments, and amphibo- Data Acquisition: Streamstown tograph rendered onto the meshed surface lites. Cur Hill represents an anticlinal synform to provide a high-resolution color 3D object (Yardley, 1974), plunging eastward at a low The laser scans were taken from a tripod (Fig. 4B). At this stage the accuracy of the scan- angle (12°–20°). Scanning was carried out in a position on the eastern side of the main quarry ner now becomes an issue. In the Streamstown small valley in which iconic folds of the Lakes (Fig. 2A). For this study we collected a single point cloud at 16 m distance the point spacing Marble Formation are found (Fig. 2B). The val- panorama scan taken with a 360° horizontal is ~10 mm, but the distance error is ±5 mm. ley is herein referred to as the Green Valley due sweep and ±40° vertical sweep from the hori- Triangulation of all the points in a point cloud, to the rich vegetation present on the lime-rich zontal. A series of seven digital photographs when the magnitude of the error approaches bedrock (Fig. 3A). The Green Valley is bisected were taken to provide the color information. the magnitude of the point spacing, produces by a stream, much of which fl ows below the sur- The digital single-lens refl ex (SLR) camera is a very irregular, “spongy” surface that is not face through carbonate caves and cavities. The mounted precisely on top of the laser scanner, an improvement over the original point cloud. outcrop surfaces are very irregular varying from which enables the RiSCAN software to calcu- It would also require an inordinate amount of near horizontal to near vertical, and it is here late the appropriate color for each point in the central processing unit (CPU) time to mesh that a spectacular exposure of Lakes Marble data cloud. A high-resolution scan set at angu- such a large data set. The Streamstown quarry Formation folds is found (Fig. 3B). The calcite lar resolutions of 0.02° horizontal and 0.12° faces are fl at with a roughness of the order of marbles at Cur Hill, comprising the formation’s vertical was then acquired over the key area of <2 mm. Given this constraint it was appropriate Upper Marble Member (Badley, 1976), display interest (the quarry walls and fl oor). This took to fi lter the point clouds using an octree fi lter superb tightly folded mesoscopic (locally D3) 25 min to acquire ~12 million individual x,y,z at 50 mm. The octree fi lter takes center of grav- folds. The fold geometry is clearly visible due position measurements on the quarry surface. ity of all points within a 50-mm cube; however, to the alternation of dark graphitic bands with This resulted in point spacing on the quarry our data lie within a band of noise that is 15 mm light-gray calcite marble bands. The outcrop walls between 5 and 40 mm depending on dis- wide. The actual location of the surface within shows excellent examples of converging “s” and tance to the quarry face. Error in the distance the data is most likely to occur at the center

590 Geosphere, June 2008 Fold visualization using virtual outcrops

Figure 2. (A) Bedrock map of Streamstown Quarry (after Naughton et al., 1992). (B) Bedrock map of Green Valley, Cur Hill.

Geosphere, June 2008 591 McCaffrey et al.

A

B C

Figure 3. Data acquisition at Cur. (A) View westward up the Green Valley. Lakes Marble Formation dips ~40° north. The abundance of thistles affected the fi nal point cloud. (B) Riegl LMS Z420i laser scanner used to collect the virtual outcrop data with the spectacular fold exposure behind the scanner. (C) Differential global positioning system (GPS) Base Station collected data to georeference the laser scans to cm-resolution.

592 Geosphere, June 2008 Fold visualization using virtual outcrops of gravity position in each cube. The resulting Following the processing and generation of VIRTUAL OUTCROPS: fi ltered point clouds contained an order of mag- the virtual outcrops, animated “fl y-throughs” of VISUALIZATION AND ANALYSIS nitude less points than the original data set. The the outcrops were generated using RiSCAN’s fi ltered point clouds where then triangulated to animation function. A series of user-specifi ed Having created the basic virtual outcrops, produce a mesh, and this surface was inspected viewpoints provide the key frames for the ani- they can be used in a variety of ways depending and where necessary corrected to remove spu- mations in RiSCAN, with a seamless transition on the desired application. Here we highlight rious triangles, and some of the more obvious between viewpoints creating the camera path. two different uses that are relevant to geoscience holes were fi lled in. The appropriate digital pho- The animations were saved in Microsoft Audio training and education. In the fi rst application, tograph was then orthorectifi ed and applied as a Video Interleave (.avi) multimedia format and an undergraduate, who was not able to visit the texture to the triangulated mesh to create a 3D serve as an excellent dynamic visualization of Streamstown quarry during the data acquisition, virtual outcrop (Fig. 4B). the study locations (see Animation 1). made a structural interpretation using the laser scanner software as part of a laboratory-based dissertation. The objective was to attempt to extract meaningful 3D geometrical data from the marble folds from the virtual outcrop, a A task that would not be possible from a standard photograph. In the second application, the Cur virtual outcrop was integrated with Google Earth and geographic information system (GIS) models to illustrate the geomorphology and geology of Cur Hill and its overall context in the larger-scale structure of Connemara. These models were used in teaching classes for groups of students before and after they carried out a fi eld visit to the site.

Picking of Structural Elements in Virtual Outcrop Data Sets

The RiSCAN software has the capability of producing planes through 3D objects from one, two, or three points that the user has defi ned in

B

Animation 1. Movie tour of the Conemara Marble Quarry at Streamstown. The movie begins with a closeup view of the fl oor of the quarry, then pans out and around to show the walls and the marble layers that display prominent folds and faults. You will need Windows Media Player or a multimedia player such as Real Player to view this fi le. If you are viewing the PDF of this paper or Figure 4. Virtual outcrop data from Streamstown Quarry. (A) The color-rendered reading it offl ine, please visit http://dx.doi point cloud shows geology from a distance, but close up, the particulate nature of the .org/10.1130/GES00147.S1 (Animation 1) or data means detail is poor. (B) A meshed surface with a draped photo provides much the full-text article on www.gsajournals.org more detail of the marble layering in the quarry. Height of face 8.84 m. to view Animation 1.

Geosphere, June 2008 593 McCaffrey et al. the data. Here, we used the three-point method marble layers in the north wall. The planes dip in the hanging wall are similar in orientation to as it is most similar to the “three-point problem” moderately to steeply to the north (Fig. 6B) in those in the north wall. The fl oor fault orienta- known to geologists. We selected three points on a uniform fashion and defi ne a small part of a tion is constrained as being 104/55°N—kine- a prominent marble layer on at least two quarry girdle distribution with a pole (β axis) plunging matics have not been established but it is likely faces (Fig. 5). A plane is drawn through the three gently to the west. to be a thrust fault (prominent thrusts are visible points to the boundaries of the data volume. Each on the south wall). plane was then inspected by moving the view to South Wall different positions to see how well it represented Structures on the south wall aligned at very Back Wall the corresponding layer. If the overall fi t is not low angles to cut faces (Figs. 6C and 6D) and The back wall contains the most impres- acceptable, then the plane is either deleted and a are therefore not as well constrained as the north sive range of fold structures, most of which are new one drawn from three different points, or the wall; however, there is some 3D control where above the fl oor fault and are continuous with the plane can be rotated to a better visual fi t. If the folds can be traced around a step in the quarry north wall (Figs. 6G and 6H). Unfortunately, plane is acceptable, then its orientation is given face. The layers in this part of the quarry show the degree of 3D control is poor as there are no by the direction vector (the pole to the plane) a range of orientations (Figs. 6C and 6D) and major steps in the face and there is only a small making sure to record plunge and trend values on average dip more gently than those in the ledge toward the bottom which provides limited downward, i.e., a lower hemisphere projection. north wall. Calculated fold hinge orientations information on the geometry of the structures Several planes are fi tted to different parts of the are varied, perhaps refl ecting the unfavorable (Fig. 6H). The approach adopted was to use the layer to defi ne an error estimate and also to cap- orientation of the left wall relative to the scan- small ledge to provide some 3D constraint on ture any nonplanar behavior. ner. In general, these β axes plunge gently to the fold hinge orientations and based on informa- west. A prominent fault that can be traced across tion already collected from the north wall (the β Results from Quarry Virtual Outcrop the south wall shows a clear hanging wall-up axis) set as a viewing direction for the RiSCAN Structural Analysis (thrust) displacement. Its orientation could not camera. This makes the assumption that fold be determined on this face but is likely to be plunges in the north wall and back wall are col- North Wall parallel to a similar structure observed in the linear. This is supported by the continuous nature The north wall is clearly the best for structural fl oor (see below). of the structures across both walls in the hanging analysis as it contains a right-angle corner where wall to the fl oor fault. In RiSCAN, if a viewing the wall steps back to the north, giving good 3D Floor direction is defi ned, then only two points picked control (Fig. 5). Due to a shadow region in the The fl oor of the quarry provides good 3D on a layer will defi ne a plane. Data produced in scan, there is a small (5-cm) gap in the render- exposures through layered marble, a discor- this way allowed some further fold properties ing that coincides with a ledge about two-thirds dance, presumed to be a fault, that cuts through to be established, e.g., limb dips and interlimb distance down the wall. By rotating the view it the layering and some patches of brecciated angles. Given the variability in fold orientation is possible to link layers above and below the marble. The marble layers below the fault (in determined in the other surfaces, assuming that gap. Each clearly defi ned layer on the north wall footwall) are clearly discordant to the layers all the folds are collinear may not be reasonable. was estimated using the three-point method at above (Figs. 6E and 6F). These layers have a minimum of fi ve times per layer. Figure 6A similar orientations to those in the south wall Geology Surrounding Quarry shows a stereonet of poles to planes fi tted to (Figs. 6E and 6F), whereas those above the fault Detailed mapping at the 1:600 scale shows that mesoscale folds surrounding the quarry have similar geometric properties to those in the quarry. The marble layering dips moderately to steeply NNW and SSE with a calculated fold axis plunging gently WSW (Fig. 6I). Measured fold axes plunge slightly (~10°–15°) more steeply, but the direction is the same as those determined in the quarry.

Compiling Multiscale Visualizations of Cur

The virtual outcrop generated from the Cur Hill data set was used to complement a series of visualizations of the topography and geology of the Cur Hill region. The visualizations were used to introduce undergraduate students from both Ireland and the United States to the out- crop using Google Earth. The site is an impor- tant location for geological fi eld courses in the Connemara Dalradian.

Figure 5. Using RiSCAN software to create a plane from three selected points Google Earth KML Content (yellow dots on image). Orientation (dip and dip direction) of the correspond- Regional geological maps of Connemara ing plane can be exported for further analysis, e.g., stereonets. were displayed in the 3D Earth viewer using

594 Geosphere, June 2008 Fold visualization using virtual outcrops A

Quarry (north wall) poles to marble layering Mean Plane 261/48 N n = 60 b = 11/271 B C

Quarry (South Wall) poles to marble layering Mean Plane 092/83 S n = 100 D b = 8/270 I E

Streamstown area poles to main fabric in black Fold hinges in red Quarry (floor) poles to marble layering Mean Plane 080/82 S Mean Plane 267/67 N n = 64 n = 100 F b = 09/259 b = 11/270 G

Figure 6. Structural interpretation of the Streamstown quarry. (A) Structural data from the north wall plotted on stereonet. (B) Planes shown in (A) in the virtual outcrop (VO). (C) Data from the south wall. (D) Mar- ble layers (green lines) traced on the south wall surface. (E) Data from fl oor region. (F) Colored point cloud of fl oor region. (G) Back wall structural data. (H) Marble lay- Quarry (Back Wall) poles to marble layering ers traced in the footwall and fl oor region. Mean Plane 264/61N H n = 333 (I) Structural data from detailed map sur- b = 10/270 rounding the quarry.

Geosphere, June 2008 595 McCaffrey et al. the KML (Keyhole Markup Language) Image photograph of the folds outcrop. This method of tized reproduction of a structural geology map Overlay function. The relationship between the presenting multimedia geoscientifi c content pro- (Yardley, 1974). Georeferenced embedded links topography and underlying geology is clearly vides an easy-to-use interactive interface through were positioned throughout the surface model demonstrated using this application. Students which users can access a variety of information using the VRML Anchor node (see Thurmond were familiar with the use of Google Earth “snippets.” Through the Google Maps interface, et al., 2005). The links provided access to photo- for this purpose and hence were suffi ciently users can gain insight into the geology of a loca- graphs, animations, QuickTime VR panoramas, “visually literate” in the context of viewing tion and choose to explore further, or quickly text fi les, Web pages, Google Earth KML fi les, 3D landscapes. However, as the spatial resolu- move to a different location. and other VRML models. To view the .kml and tion for the Cur area in Google Earth is poor vrml fi les, see http://geoscene.ie/geosphere/ (in contrast to the high-resolution QuickBird VRML Surface Models index.htm. imagery at the Streamstown locality), it was A higher-resolution visualization of Cur Hill necessary to use the virtual outcrop data to gain than that available in Google Earth is provided Virtual Outcrops an improved resolution. by a 3D VRML surface model of Cur Hill and Finally, after providing a background to the the surrounding landscape (~3 km2) generated Dalradian geology of Connemara and putting Google Maps Content using a 50-m digital elevation model (DEM). the location of the Lakes Marble Formation The locations for both virtual outcrops are The DEM consisted of 3721 points (61 × 61). outcrop in the context of the locality, students displayed in a customized Google Map, using The VRML model was generated using Pavan were shown animations generated in RiSCAN the Google Maps API (Application Program- software, which is a VRML compiler and proj- from the Cur data set (Figs. 8 and 9). The focus ming Interface). JavaScript functionality enables ect management system for the MapInfo GIS was primarily on the iconic folds outcrop. Pho- placemarks to be positioned at specifi c locations software. Navigable 3D VRML models were tographs and QuickTime panoramas were used and may be confi gured to have pop-up informa- generated from geospatial data in MapInfo for- to reinforce the communicative effi ciency of 3D tion windows (Fig. 7). A tabbed window was mat. The VRML surface model was reproduced animations. This enabled students to visualize used for the Cur Hill virtual outcrop. Three types with a variety of textures, such as OSi (Ord- the outcrop from a variety of perspectives. Ani- of media were presented: a QuickTime virtual nance Survey of Ireland) color aerial photog- mations showing the location and nature of the reality (VR) panorama of the site; a QuickTime raphy; Geological Survey of Ireland 1:100,000 fold outcrop were used to communicate the geo- movie of the scanner in operation at Cur; and a bedrock geology; and a georeferenced, digi- logical architecture of the valley. For example,

Figure 7. Google Maps tabbed info-window showing embedded QuickTimeVR panorama, QuickTime movie, and imagery.

596 Geosphere, June 2008 Fold visualization using virtual outcrops

Figure 8. Virtual outcrop data from the Green Valley at Cur Hill. View toward northwest. Faulting in the amphibolite clearly visible. Field of view ca. 20 m at front of model.

Figure 9. Virtual outcrop data from the Green Valley at Cur Hill. The iconic D3 folds in the Upper Marble Member. Outcrop width 2.5m.

Geosphere, June 2008 597 McCaffrey et al. faulting in the amphibolites in the northern cliff The generation of a virtual outcrop from the The effectiveness of the animations in com- faces is clearly visible in the virtual outcrop. Cur Hill data set proved to be a labor-intensive municating information about the two geo- task owing to the geometry of the point cloud logical outcrops cannot always be assumed to DISCUSSION captured at the location (Animation 2). The pri- have a positive outcome. In consideration of mary diffi culty concerned vegetation cover at the Principle of Apprehension (Tversky et al., Geometrical Interpretation the site on the day of the scanning. Figure 3A 2002), animations can often fail to communi- demonstrates the abundance of thistles at the cate familiar visual content to the observers, Variations between the map data and the vir- outcrop. The resultant point cloud contained a and can overwhelm the viewer with abstract tual outcrop–derived data are mostly a result signifi cant amount of data that did not refl ect graphic illustrations of imperceptible features of the different scales of observation. Structure the topography of the outcrop. Meshing the raw and scales. To overcome this potential mis- in the vicinity of Streamstown is dominated point cloud created a very irregular and errone- communication, the virtual outcrops (VOs) are by upright, gently WSW-plunging, mesoscale ous surface model. While a signifi cant amount supplemented by photography and QuickTime folds. Within the quarry, folds have a similar of time was spent cleaning up the point cloud to panoramas to give the observer an alternative geometry to the regional data sets with calcu- remove vegetation profi les at specifi c locations, method of visualizing the outcrops. These addi- lated fold axes that are gently WSW plunging it was not possible to remove all the vegeta- tional media are retrievable through embedded in all cases. Different parts of the quarry are tion. As scanning was carried out at the height links in the regional VRML models and through dominated by different average dips ranging of summer, we suggest that scanning at similar customized Google Maps. Using the informa- from moderately NNW dipping to steeply SSE locations be carried out in winter or early spring tion pop-up window in Google Maps, Quick- dipping, but this depends on which part of the when vegetative cover is minimal. Time VR content and QuickTime movies can be larger mesoscale folds that part of the quarry is embedded in the Google Maps interface. How- exposing and also location relative to the fault The Benefi ts of Virtual Outcrop Technology ever, no known support for QuickTime content exposed in the quarry fl oor. The Streamstown is available in Google Earth at present. example shows that it is clearly feasible to Virtual outcrops offer students the possibil- Virtual outcrops technology can bring the extract 3D structural information from the vir- ity to study outcrops from localities they are most spectacular outcrops worldwide direct to tual outcrop; however, due to access reasons it not able to visit. In our Streamstown exam- the student no matter where they are based as has not been possible to verify the virtual data ple, data collection took place in the summer long as they have an Internet connection. These against a data set measured in the outcrop. The when the students were not available, yet they models have great potential for introducing geol- quarry is somewhat unique in that the smooth, still generated a useful structural data set and ogy to a wide sector of the public who would fl at walls cut in different orientations help inter- made a good attempt at interpreting the out- not, for whatever reason normally visit such pretation in some cases where there was a cor- crop. This exercise shows how virtual outcrop sites, for example, students with disabilities, ner available to pick on two surfaces. In other technology could provide good structural middle and high school students, or interested places, such as the back wall, this causes a prob- geology training and supplement traditional amateurs. As the technology becomes cheaper lem because there was no edge available to give fi eld classes. For example, Figures 4, 5, and and more data sets become available, we sug- a required 3D component. 6 were generated by the students as part of gest that interpretation of virtual outcrops will The virtual outcrop of the Green Valley at Cur their laboratory dissertation and illustrate the become an important part of the earth science clearly shows folding in the upper marble mem- type of analysis possible from virtual outcrop curriculum. They will provide supplementary ber. This iconic outcrop is often reproduced in technology. During the project, the students photographs (see cover of Leake and Tanner, had to reexamine the fundamental concepts of 1994; Yardley, 1989, p. 26). The virtual outcrop structural geology (dip, strike, plunge, and azi- provides useful information on the 3D geometry muth) to ensure that they were collecting valid of the outcrop, for example. The plunge direc- data. This training is normally only available tion can be determined from the model either during relatively short fi eld trips, and students qualitatively by rotating the view or quanti- are likely to benefi t from being able to prac- tatively using the same method as we used in tice these measurements during a longer-term the quarry. The virtual outcrops are used as a laboratory project. resource for students to access prior to visiting The generation of VRML models, using the location and provide visual content for post- high-resolution aerial photography and DEMs, fi eldwork discussions and revision in the context exposes students to the concept of spatial multi- of the regional structure. The structural geology dimensionality, when used in conjunction with of Connemara is complex because of the pres- Google Earth content and virtual outcrop data. ence of major refolded fold structures. How- Students can be shown how the topography and ever, the use of Google Earth and Google Maps surface cover can sometimes refl ect the under- Animation 2. Movie panorama of Green to communicate the regional geological context lying geology. This is particularly true with the Valley, Cur Hill, Conemara, western Ire- enables instructors to create effective visual VRML aerial photography model of Cur Hill, land. You will need Windows Media Player content for classroom and fi eld-study-related whereby the surface signature over the Lakes or a multimedia player such as Real Player teaching. Because Google Earth and Google Marble Formation shows rich green vegetation, to view this fi le. If you are viewing the PDF Maps are freely available, they are excellent while the surface signature over the amphi- of this paper or reading it offl ine, please tools for displaying custom maps and data, as bolites indicates poorly drained ground, with visit http://dx.doi.org/10.1130/GES00147. well as enabling students to have remote access clearly visible, east-west–trending lineaments S2 (Animation 2) or the full-text article on (via intranet or Internet) to course content. following the strike. www.gsajournals.org to view Animation 2.

598 Geosphere, June 2008 Fold visualization using virtual outcrops

Sedimentary Research, v. 75, no. 2, p. 166–176, doi: outcrop studies in North Africa: First Break, v. 25, resources for existing fi eld classes and help to 10.2110/jsr.2005.013. p. 81–87. further broaden students’ knowledge base by Clegg, P., Trinks, I., McCaffrey, K., Holdsworth, B., Jones, Rosser, N.J., Petley, D.N., Lim, M., Dunning, S.A., and providing examples from worldwide databases. R., Hobbs, R., and Waggott, S., 2005, Towards the vir- Allison, R.J., 2005, Terrestrial laser scanning for tual outcrop: Geoscientist, v. 15, p. 8–9. monitoring the process of hard rock coastal cliff ero- A fi nal point is relevant to the ongoing debate Enge, H.D., Buckley, S.J., Rotevatn, A., and Howell, J.A., sion: Quarterly Journal of Engineering Geology and regarding public access rights to land in Ireland 2007, From outcrop to reservoir simulation model: Hydrogeology, v. 38, p. 363–375, doi: 10.1144/1470- Workfl ow and procedures: Geosphere, v. 3, p. 469–490, 9236/05-008. and other countries, and the concerns geoscien- doi: 10.1130/GES00099.1. Sagy, A., Brodsky, E.E., and Axen, G.J., 2007, Evolution of tists have about the future of fi eld visits to geo- Friedrich, A.M., Bowring, S.A., Hodges, K.V., and Martin, fault surface roughness with slip: Geology, v. 35, no. 3, logically important sites. Through the use of M.W., 1999, A short-lived continental magmatic arc in p. 283–286, doi: 10.1130/G23235A.1. Connemara, Western Irish Caledonides: Implications Stanley, S.M., 1999, Earth system history: New York, W.H. virtual outcrops for student instruction, some of for the age of the Grampian orogeny: Geology, v. 27, Freeman and Company, 615 p. these concerns can be overcome. However, we p. 27–30, doi: 10.1130/0091-7613(1999)027<0027: Tanner, P.W.G., Dempster, T.J., and Dickin, A.P., 1989, emphasize that geological visualizations such SLCMAA>2.3.CO;2. Short paper: Time of docking of the Connemara terrane Graham, J.R., Wrafter, J.P., Daly, J.S., and Menuge, J.F., with the Delaney Dome Formation, western Ireland: as terrestrial scanner–generated virtual out- 1991, A local source for the Ordovician Derryveeny Geological Society [London] Journal, v. 146, no. 3, crops and 3D surface models cannot substitute Conglomerate Formation, western Ireland: Implica- p. 389–392, doi: 10.1144/gsjgs.146.3.0389. tions for the Connemara Dalradian, in Morton, A.C., Thurmond, J.B., Drzewiecki, P.A., and Xueming, X., 2005, for “real-world” experiences of fi eld geology. Todd, S.P., and Haughton, P.D.W., eds., Developments Building simple multiscale visualizations of out- Nevertheless, visualizations can serve as aids in in sedimentary provenance studies: Geological Society crop geology using virtual reality modeling language the learning process and provide valuable tools [London] Special Publication, v. 57, p. 199–233. (VRML): Computers & Geosciences, v. 31, no. 7, Harris, A.L., and Pitcher, W.S., 1975, The Dalradian Super- p. 913–919, doi: 10.1016/j.cageo.2005.03.007. for “bringing” remote or inaccessible outcrops group, in Harris, A.L., et al., eds., A correlation of the Trinks, I., Clegg, P., McCaffrey, K., Jones, R., Hobbs, R., to students. Precambrian rocks in the British Isles: Geological Holdsworth, B., Holliman, N., Imber, J., Waggott, S., Society [London] Special Report, v. 6, p. 52–75. and Wilson, R., 2005, Mapping and analysing virtual ACKNOWLEDGMENTS Harris, D.H.M., 1995, Caledonian transpressional terrane outcrops: Visual Geosciences, doi: 10.1007/s10069- accretion along the Laurentian margin in County Mayo, 005-0026-9. Ireland: Geological Society [London] Journal, v. 152, Tversky, B., Morrison, J., and Betrancourt, M., 2002, Ani- The authors thank Ambrose Joyce Sr. and no. 5, p. 797–806, doi: 10.1144/gsjgs.152.5.0797. mation: Can it facilitate?: International Journal of Ambrose Joyce Jr. for access to the Streamstown Leake, B.E., and Tanner, P.W.G., 1994, The geology of the Human-Computer Studies, v. 57, p. 247–262, doi: Quarry and Alan McCaffrey for help with the laser Dalradian and associated rocks of Connemara, western 10.1006/ijhc.2002.1017. scanning. The authors acknowledge funding for this Ireland: Dublin, Royal Irish Academy, 96 p. Wawrzyniec, T.F., McFadden, L.D., Ellwein, A., Meyer, project from the Heritage Offi ce, Galway County McCaffrey, K.J.W., Jones, R.R., Holdsworth, R.E., Wilson, G., Scuderi, L., McAuliffe, J., and Fawcett, P., 2007, R.W., Clegg, P., Imber, J., Holliman, N., and Trinks, I., Chronotopographic analysis directly from point-cloud Council and the Heritage Council of Ireland. Hen- 2005, Unlocking the spatial dimension: Digital tech- data: A method for detecting small, seasonal hillslope nessy acknowledges a postgraduate fellowship award nologies and the future of geoscience fi eldwork: Geo- change, Black Mesa Escarpment, NE Arizona: Geo- from the Irish Council for Science, Engineering and logical Society [London] Journal, v. 162, p. 927–938, sphere, v. 3, p. 550–567; doi: 10.1130/GES00110.1. Technology (IRCSET). A special word of thanks is doi: 10.1144/0016-764905-017. Xu, X., Aiken, C.L.V., and Nielsen, K.C., 1999, Real time made to Ms. Marie Mannion, Heritage Offi cer, Gal- Naughton, E., Feely, M., and Bell, A., 1992, The assessment and the virtual outcrop improve geological fi eld map- way County Council. We thank Amy Ellwein and an of the Connemara marble resources: Galway, Ireland, ping: Eos (Transactions, American Geophysical Union), anonymous reviewer for their constructive comments. National University of Ireland, Department of Earth v. 80, no. 29, p. 317, doi: 10.1029/99EO00232. and Ocean Sciences, Unpublished Report commis- Xu, X., Aiken, C., Bhattacharya, J.P., Corbeanu, R.M., sioned by the Connemara Marble Producers Group. 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