REPORT:
Basic Photography at Mount St. Helens
and Other Cascades Volcanoes

Abstract

During the last decade, researchers at the Cascades Volcano Observatory (CVO) in Vancouver, Washington, have taken thousands of photographs of Mount St. Helens and the surrounding area, and hundreds more of other Cascades volcanoes. They have used a great many types of cameras. Cameras are one of the most versatile and useful tools available to document changes around volcanoes. Still cameras take one picture at a time and can be divided on the basis of film size into small format, medium format, and large format. There is also an instant-processing still camera which produces a single image within 30 seconds. Video and movie cameras are used for many of the same applications as still cameras are are especially useful in oblique and illustrative terrestrial photography. Video or movie footage is valuable when studying dynamic events such as ash plumes or pyroclastic flows, or calculating the speed of lahars or floods. Vertical and oblique aerial photography, repeat and illustrative terrestrial photography, and time-lapse photography are all techniques available for documenting changes occurring on or around volcanoes. the resulting photographs and footage can be used for interpretation, illustrations in publications, scientific talks and public slide shows, quantitative measurements, and historical documentation of volcanic processes.

Introduction

Active volcanoes are capable of producing great changes in themselves and the surrounding landscape. To illustrate, document, and to better understand these changes, photographic records should be kept.

On May 18, 1980, over 400 meters of Mount St. Helens collapsed as a series of great landslides, releasing pressure which produced a 20 kilometer-high plinian ash column, and leaving behind a crater 1.5 kilometers wide and 600 meters deep. Over 650 square kilometers of the Toutle River valley was buried by 2.8 cubic kilometers of debris from the collapsing cone (Tilling, 1984). The magnitude of change is clearly illustrated by comparing photographs taken from a site 10 kilometers northwest of Mount St. helens on May 17, 1980, the day before the devastating eruption (fig. 20.1A), and from the same location of September 10 (fig.20.1B). The same view taken on March 30, 1987, illustrates the continuing changes to the landscape after 7 years of dome growth and river channel erosion (fig. 20.1C).

Figure 20.1: Mount St. Helens as viewed from ten kilometers to the northwest, showing development of the lava dome and drainage channels.
	Figure 20.1A One day before the devastating May 18, 1980 eruption.
	Figure 20.1B Four months after the May 18, 1980 eruption.
	Figure 20.1C Seven years after the May 18, 1980 eruption.

During the last decade, personnel at the Cascades Volcano Observatory (CVO) have taken thousands of photographs of Mount St. Helens and the surrounding area, and hundreds more of other Cascades volcanoes. These photographs are used for illustration in publications, scientific talks and public slide shows, quantitative measurements and interpretation, and historical documentation of volcanic processes. Many camera types are used including still cameras, video cameras, and movie cameras. Many techniques are employed including vertical and oblique aerial photography, repeat and illustrative terrestrial photography, and time-lapse photography. The type of equipment and the purpose for which the equipment or technique is used largely depend upon the scientific need, budget limitations, location accessibility, and the scientist's personal preference. This chapter covers possible combinations of cameras and techniques and cites examples of what has been useful at Mount St. Helens and other Cascades volcanoes. There is no correct or universal way to photograph volcanoes; how little, how much, or of what quality depends upon variables unique to each volcano and to the scientists involved.

Still Photography Cameras

Cameras are one of the most versatile and useful tools available to scientists monitoring volcanoes, and still cameras are the most commonly used. Still cameras take one picture at a time resulting in either positive or negative images, and can be divided on the basis of film size into small format, medium format, and large format. There is also an instant-processing still camera, which produces a single image within 30 seconds. the scientists at CVO use all four.

Small-Format Cameras

The most common small-format cameras use 35-mm-size roll film, producing 12-36 frames per roll. These cameras are readily available, economical, convenient to use, and offer a wide variety of lenses and accessories. Film is available in a wide range of types and speeds, and processing is quick, with certain films able to be processed in the office. For a detailed scientific study, however, the small images may not have sufficient resolution to show the detail needed to compare landscape changes, and high-quality enlargements are often difficult and expensive to obtain. Two styles of small-format cameras used at CVO are the 35-mm lens/shutter and the 35-mm single-lens reflex (SLR).

The lens/shutter is a camera where the user looks through a viewfinder, not the lens, resulting in a photo that is slightly offset from what is actually viewed. The lens/shutter cameras at CVO are usually auto-load, auto-focus, and auto-rewind, and are often referred to as "point-and-shoots". Lenses are either a single fixed focal length or zoom between two focal lengths. The cameras are generally small and lightweight, and are easily carried in pockets or packs. Because the cameras are typically cheaper than SLR's, they are often considered "disposable" cameras, and are used while stream-gaging, surveying drainage-channels, working in dusty or ashy areas, or doing activities when there is a chance of the camera (or the scientist) falling into a river or becoming covered with dust and ash.

The camera most commonly used at CVO is the 35-mm SLR. In the SLR, the image coming through the lens is reflected to the viewfinder by a mirror and a prism, so the user sees exactly what the film records. These cameras are relatively compact, lightweight, and can use a large selection of interchangeable lenses and accessories. Many different brands of SLR's are used, as each researcher buys camera equipment to fit his or her scientific needs, project budget restrictions, and personal taste. For example, many use the Olympus OM2 or the Nikon FE, both of which have proved dependable in Mount St. Helens ashy environment. Others use the Minolta X700 with its optional multifunction programmable data back. This data back can record hours, minutes, and seconds on the film, a valuable feature when documenting dynamic events such as ash plumes, pyroclastic flows, lahars, and floods. The Minolta data back can also be programmed to trigger the camera every 1 second to every 99+ hours, or an optional motor drive can be set to trigger 2 or 3.5 frames per second, options that have been important in time-lapse photography sequences.

The standard 50-mm focal-length lens is most commonly used with the SLR's. This lens is ideal, as it provides approximately the same magnification as the human eye. The wide-angle 28-mm focal-length lens is also popular and forms an image of a subject which is approximately half the size of that formed by the standard lens.

Only a few scientists use medium-range telephotos (100 to 300-mm focal-lengths), long-range telephotos (300 to 1000-mm focal-lengths), or zoom lenses, as these lenses are expensive and bulky. In the field, most scientists usually carry only one camera body and lens, as extra bodies and lenses take up room and add extra weight; moreover, it is often unwise or difficult to change lenses in ashy, dusty, or winter environments. Occasionally field crews carry a variety of cameras and lenses, resulting in different scale photographs of the same subject on the same day, a convenience when choosing photographs for publication or slide shows. For example, one member of CVO's deformation monitoring crew routinely uses a Nikon with a 28-mm lens, while another uses a Nikon with a 50-mm lens.

The CVO staff photographer uses a Nikon FE with a Vivitar 17-mm lens, and Nikkor 28-mm, 55-mm, and 200-mm lenses. The 17-mm is a super-wide-angle lens with a field of view of approximately 100 degrees (as measured from corner to corner) and is useful when photographing scientists working in their environment (fig. 20.2A). The 28-mm is a wide-angle lens with a field of view of approximately 75 degrees and is useful when photographing aerial views of the crater or dome (fig. 20.2B). The standard 55-mm lens has a field of view of approximately 45 degrees and is an excellent all-around lens, useful for all types of photography (fig. 20.2C). The 200-mm lens is a medium-range telephoto lens with a field of view of approximately 12 degrees and is useful when photographing the dome from a distance (fig. 20.2D). During critical periods, the staff photographer also carries a Minolta X700 with its hours-minutes-and-seconds data back, a motor drive, and an MD 50-135-mm zoom lens, or an extra Nikon FE body and Nikkor 35-105-mm zoom and 100-300-mm zoom lenses. Multiple cameras allow the simultaneous use of different types of films and provide an extra camera should the primary camera be inoperable.

Figure 20.2: Mount St. Helens photographed using different focal-length lenses.
	Figure 20.2A A 17-mm lens was used to photograph researchers making measurements to the dome.
	Figure 20.2B A 28-mm lens was used to photograph an aerial view of Mount St. Helens crater and dome.
	Figure 20.2C A 55-mm lens was used from 8 kilometers away to photograph a small steam and ash burst.
	Figure 20.2D From the same location as C, a 200-mm lens was used to photograph the steamy lava dome and the remnants of a rockslide down its north face.

A wide selection of film types is available to users of 35-mm small-format cameras. At CVO, most scientists participate in scientific talks and slide shows and thus prefer color transparency (slide) films over color or black-and-white (b/w) negative films. Transparencies are also economical, easy to view, convenient to store, and for most applications can easily be made into b/w or color prints. Kodak brand film is generally used, with Kodachrome 64 and Ektachrome 200 transparency films being the most popular. Both of these films provide good color and show little grain. The faster speed Ektachrome 400 transparency film is often used when photographing during overcast or rainy periods.

Very little black-and-white film is used by CVO researchers, as they usually carry only one camera and have it loaded with color. The staff photographer, however, routinely carries two cameras, one loaded with color slide film and the other loaded with a fine-grained b/w negative film. The b/w film is used when shooting specifically for publication photographs or historical documentation. Black-and-white film is very important for historical archiving. According to Eastman Kodak Co. (1979, p.32):

"When black-and-white negatives on acetate or polyester film base are processed properly, and are protected in storage from the effects of heat, moisture, oxidizing gases, and reactive storage materials, they are extremely stable articles. They will outlast most other photographic records and, since they can be duplicated with very little loss of quality by a comparatively simple process, they constitute the best material for archival purposes."

Medium-Format Cameras

Few medium-format cameras are used at CVO. One scientist uses a Pentax 6x7 with a standard Takumar 105-mm lens. The staff photographer uses a Hasselblad 500C with a standard Planar 80-mm lens and a wide-angle Distagon 50-mm lens. Since most medium-format photographs are used for publication or historical documentation, fine-grained b/w films are generally used. A second Hasselblad film back is carried loaded with either color slide or color negative film.

Large-Format Cameras

At CVO, large-format cameras are used for vertical aerial photography and most CVO requirements are contracted to professional aerial photography companies. In 1985, "in-house" large-format vertical aerial photography was attempted with a borrowed Fairchild camera. A local aircraft company was contracted to cut a camera port for the camera in the belly of its airplane. The project was abandoned after a short time, however, owing to the poor quality of the camera and the resulting photographs.

Instant-Processing Cameras

Video and Movie Cameras

Video and movie cameras are used for many of the same applications as still cameras and are especially useful in oblique and illustrative terrestrial photography. Video or movie footage is valuable when studying dynamic events such as ash plumes or pyroclastic flows, or for calculating the speed of lahars or floods. When shown at talks or seminars, video or movie footage allows the scientific and public community to feel what it is like to be at an active volcano.

CVO has made only limited use of video or movie cameras as an illustrative tool, and numerous public-education opportunities have been lost simply because video or movie cameras were not taken into the field to take appropriate footage of the crater, dome, or scientists working. Such cameras have been and are being used in individual scientific projects, however. One project was the 1980-82 closed-circuit television/video system installed on Harry's Ridge (Miller and Hoblitt, 1981), and a similar project currently in use employs a slow-scan video system to relay real-time images of the crater to the offices at CVO (Furukawa and others, chapter 19). In 1986-87, a low-light television/video system was installed on the Toutle River for viewing the river channel during lahars or floods (Jon Major, oral commun., 1990), and from 1981-86, a night-vision system consisting of video and still cameras was used to monitor changes in the system of hot cracks on the lava dome (Robin Holcomb, oral commun., 1990). A 16-mm movie camera was used in 1981-83 to study debris flows originating from Shoestring Glacier on Mount St. Helens (Tom Pierson, oral commun., 1990), and in 1988 and 1989, 8-mm movie cameras were used to monitor glacial outburst floods originating from South Tahoma Glacier on Mount Rainier (Joe Walder, oral commun., 1990). Movie cameras were also successfully used to photograph sequences of active dome growth during the 1982 and 1986 dome-building episodes at Mount St. Helens.

Video cameras are available in 1-inch, 3/4-inch, 1/2-inch, and 8-mm tape formats. They offer the luxury of convenience; footage shot on videotape can be instantly reviewed and studied back at the office, thereby offering quick interpretation and response to possible hazards. Prints can be made from a single video frame, a technique that has been used to compare hot cracks on the dome preceding an eruptive episode. Such prints are generally of much lower resolution than either still or movie film however. Most video cameras also record sound simultaneously with the video, so that the photographer can narrate the scene and describe exactly what is being observed.

There is no one ideal video camera system among the many types of video cameras available; cost and personal preference are major factors in deciding which camera to purchase. One popular video-camera design is the "camcorder," a system where the recording tape is mounted in the camera body. In 1989, four camcorder systems in use at CVO were; 1/2-inch Panasonic AG-160 ProLine VHS, JVC GF-S550 SuperVHS, and JVC Handycam "Environmental Quality" system. One-half-inch VHS and SuperVHS systems are economical, readily available, and offer good quality images; their tapes can be purchased at nearly every camera store or supermarket (a useful feature when in the field). The 1/2-inch JVC "Compact" and the 8-mm Sony "EQ" systems are small and lightweight and fit easily into backpacks. The Sony "EQ" camcorder is weather resistant and ashproof. Its 8-mm blank tapes are not as readily available as the 1/2-inch format tapes, however. This camera is popular with the scientists, as they do not have to carry a bulky camera around yet can still enjoy viewing the scene immediately when back in the office.

CVO uses two formats of movie cameras, a 16-mm and an 8-mm-size format. The 16-mm offers better quality, but the 8-mm is lightweight, economical, and more convenient to use. In 1989, three types of movie cameras in use at Mount St. Helens were a 16-mm Canon Scoopic, an 8-mm Canon Auto Zoom 518 Super-8, and three 8-mm Eumig 128 XL Super-8 movie cameras, modified for time-lapse by Timelapse, Inc. The Eumigs are in weatherproof housings that can be easily mounted on a tripod, and the time-lapse feature is programmable from one frame every 0.5 seconds to one frame every 99.5 minutes.

CVO has used movie cameras to obtain "one-of-a-kind" footage. On May 18, 1980, a CVO geologist shot 700 feet of 16-mm movie film of Mount St. Helens' eruption plume. This footage has been repeatedly requested by video and movie companies and television producers during the past 10 years. For security and protection against damage to the film, the original is now kept under lock and key and a copy negative is kept on file. Duplicate films and videotapes are sent to prospective users, and all reproductions of the footage are made from the file negative. This procedure is highly recommended to anyone obtaining irreplaceable footage. In 1982 and 1986, one-of-a-kind dome-eruption footage was filmed using the modified Eumig 8-mm movie cameras. The cameras photographed growth of emerging lobes on the lava dome.

Unfortunately, movie-camera formats are becoming more difficult to effectively find and use, owing to the popularity of video camera systems with the general public. Some camera companies that manufactured 8-mm movie cameras are simply no longer doing so, and some film laboratories are phasing out the processing of movie film.

Techniques

Vertical and oblique aerial photography, repeat and illustrative terrestrial photography, and time-lapse photography are all techniques available for documenting changes occurring on or around volcanoes. Any and all types of cameras can be used. To ensure a successful photographic trip, pay attention to four main points.

Camera Protection

Volcanic ash and gases destroy cameras. Ash scratches camera lenses and film and can jam the camera's internal mechanisms, while volcanic gases corrode the camera body and the delicate circuits of electronic cameras. To protect the camera against ash and gas, keep it in a case or camera bag when not in use and load film in a protected environment. Use clear filters (such as "UV" or "Skylight" filters) to protect the lens surface. Filters are expendable and more economical to replace than the cameras lens. Have the camera system cleaned regularly. Take extreme care when using video systems in ashy volcano environment, as even the slightest dusting of ash can interfere with the recording heads.

Low-temperature Photography

Volcanic activity occurs during cold winter months as well as warm summer ones, creating a problem with camera operation in freezing weather. Cameras continually exposed to freezing temperatures become sluggish as mechanical reaction time increases (shutter speeds lengthen). Film freezes and becomes brittle, and camera batteries lose their efficiency at low temperatures. To alleviate these problems, keep camera and extra film warm by carrying it near the body under out garments, and if available, install fresh silver oxide or lithium batteries before venturing into the field. Silver oxide and lithium batteries perform better in cold temperatures than the regular alkaline types (Gillsater, 1985, p.33). Always carry extra batteries. Frozen film should be thawed at least an hour before using.

Bracketing Exposures

When photographing volcanoes, film is usually the cheapest factor involved, so take many fames of the same subject using different exposure settings. Shoot one frame as the camera lightmeter indicates, then bracket exposures by increasing exposure (overexposing) and decreasing exposure (underexposing) for the next frames. In extreme conditions, increase or decrease exposures by one and two stops, depending upon the subject. For example, the correct exposure for dark objects (as Mount St. Helens' dome) surrounded by brightly-lit snow will generally be one or two stops of increased exposure from that which the lightmeter indicates. Conversely, photos of a snow-covered peak surrounded by blue sky and green forest often are washed-out if shot at the exposure the lightmeter indicates. Therefore, decrease exposure by one or two stops to properly expose for the snowy peak. Ash, mud, and snow are difficult subjects to photograph, for they have very little inherent color and contrast, and in these situations, most camera lightmeters have difficulty indicating the correct exposure. By bracketing exposures, the proper exposure -- not necessarily the the camera meter indicates -- may be obtained. To bracket exposures on automatic cameras, use the "exposure-compensation dial" and adjust to the plus side to increase exposure and to the minus side to decrease exposure.

Accurate Notes

Keeping accurate notes may be the most important aspect of volcano photography, other than the actual shooting of the photography. Keep notes on cameras, lenses, and filters used, film type, exposure, date and time, weather and lighting conditions, the height of the tripod, the subject being photographed, and the location from where the photography was taken. Keep notes on everything and anything that might be important, for they may prove useful years later.

Vertical Aerial Photography

Vertical aerial photographs (figs. 20.3 and 20.4) are taken when the camera's optical axis is pointing downward, within 20 degrees of vertical (Ray, 1960, p.2). The cameras (usually large format, occasionally medium format, and rarely small format) are mounted in the belly of an aircraft and shoot through a camera port. The aircraft flies in straight lines back and forth across an area, following predetermined flightlines. A flightline consists of three or more photographs taken in measured succession, with each photograph overlapping adjacent ones by 30 to 60 percent. Vast areas of ground can be photographed in a few minutes. The flightlines at Mount St. Helens were designed to document the impact of volcanic eruptions on the peak and the subsequent changes occurring within the crater and surrounding river valleys after the May 18 eruption.

The photographic scale of vertical aerial photography varies and is determined by the focal length of the lens used divided by the altitude of the aircraft above the ground, expressed in a ratio. The lower the altitude or the longer the focal length, the larger the photographic scale is and the more detail that can be seen (fig. 20.3).

Photographic scale is only an approximation at best, as topographic relief of the terrain photographed and the inclination of the optical axis of the camera are two major factors that cause variation in scale (Miller and Miller, 1961, p.8). For example, at Mount St. Helens a flightline over the crater and north to Spirit Lake is flown at an altitude of 7.6 kilometer (25,000 feet). A 152-mm (6-inch) focal-length lens is used, and approximately six frames are photographed. A single frame can cover the entire dome, crater and flanks of the volcano (fig. 20.3A). Photographic scale of that frame ranges from 1:42,000 around the flanks of the volcano, to 1:40,000 across the crater floor, to 1:34,000 at the crater rim. Another flightline is flown at an altitude of approximately 2.7 kilometers (9,000 feet) and photographs are taken using the same lens. A single frame covers the dome (fig. 20.3B). This photograph has a larger scale than the previous photograph (hence more detail can be seen), and its scale ranges from approximately 1:8,000 at the base of the dome to 1:6,000 on top of the dome.

Figure 20.3: Large-format vertical aerial photographs, reduced, illustrating different photographic scales.
	Figure 20.3A: Mount St. Helens crater and dome photographed from 7.6 kilometers (25,000 feet), showing crater floor at a scale of approximately 1:40,000 (before reduction).
	Figure 20.3B: Lava dome photographed from 2.7 kilometers (9,000 feet), showing top of dome at a scale of approximately 1:6,000 (before reduction).

By 1990, the flightline over Mount St. Helens crater and dome had be rephotographed over 150 times. All photography was contracted to professional aerial photography companies, altitudes and photographic scale varied, and b/w and color negative film was used.

Figure 20.4: Large-format vertical aerial photographs, reduced 50 percent, illustrating drainage channel development around Mount St. Helens at a scale of approximately 1:9,600.
	Figure 20.4A: Section of debris avalanche photographed September 15, 1980, shows absence of drainage channel development. Letters A,B,C are for orientation with 20.4B.
	Figure 20.4B: Same area photographed September 28, 1985, shows establishment of major drainage channels. Letters A,B,C are for orientation with 20.4A.

In June 1980, over 100 flightlines specifically designed to document drainage-channel development around Mount St. Helens were established (fig. 20.4), and these flightlines were rephotographed yearly during the low water season and after major hydrologic events. Scale was 1:9,600, and b/w film was used (with color film being used occasionally in 1980). Flightlines varied in length from 3 to over 20 frames depending upon the straight length of the drainage reach. Large drainages would typically have many flightlines, whereas small drainages were covered by one flightline (fig. 20.5).

Figure 20.5: Section of a location map showing layout of flightlines over drainage channels southeast of Mount St. Helens. Contours in feet. Numbers on the flightlines are indexed to the CVO photo library. Circled numbers within bold arrows refer to interpretive features described on the original base map (U.S.Geological Survey, 1981). Click on map for larger area (155K,GIF).

The individual photographs from flightlines can be pasted together and read like a map. The overlapping areas of two adjacent photographs form stereoscopic pairs that can be used to directly see elevation differences in the photographed terrain. With the proper support equipment, stereoscopic pairs can be used to create topographic contour maps. At Mount St. Helens, photography flown after each dome-building episode or after major hydrologic events has been used to produce numerous topographic maps of the crater, dome, and debris avalanche.

The value of vertical aerial photography was proved at Mount St. Helens in 1980 (Moore and Albee, 1981). A topographic map was made from photography flown across the volcano on April 12, 23 days after earthquake activity began. This map was compared with a published 1958 contour map (based on 1952 photographs) and significant topographic differences were noted. To eliminate possible changes due to glacial action during the 28-year span covered by the maps, a new topographic map was "hastily prepared" from photography of August 15, 1979, and compared with the April 12, 1980 map. Differences in elevations of the summit graben and bulge area on the north side of Mount St. Helens were apparent. According to Moore and Albee (1981, p.127):

"The photogrammetric data *** in conjunction with ground geodetic measurements *** were of prime importance in understanding the processes acting within the volcano and in assessing the hazard due to oversteepening of the north slope. In retrospect, the photogrammetric data set was acquired at low risk, and consequently should be an important element in monitoring future activity of potentially explosive volcanoes of similar type."

Oblique Aerial Photography

Oblique aerial photographs (fig.20.2B) are taken when the camera's optical axis is considerably inclined from the vertical, generally 20 degrees or more (Ray, 1960, p.2). Krimmel and Post (1981, p.31) believe that this technique is one of the more useful photographic techniques used at volcanoes.

"Oblique aerial photographs offer many advantages over vertical photographs for documentation of volcanic events; these include more natural perspective, greater aerial coverage from low altitude, greater flexibility in aircraft operation, coverage of specific localities during periods of partial cloud or ash obscuration, and lower cost."

Small-format 35-mm cameras loaded with color slide film are the most common camera format and film used at CVO for oblique aerial photography of the Cascades volcanoes. A medium-format camera loaded with b/w film is also used by the staff photographer. (Although no common, a large-format camera can also be used for oblique aerial photography; see Krimmel and Post, 1981). Video or movie cameras are occasionally used. The cameras are always hand-held (except for the large-format camera used by Krimmel and Post, which is mounted in the airplane). The most useful lenses for oblique aerial photography are the standard and wide angle, as the telephoto lens magnifies aircraft vibrations, making it difficult to use with complete success.

The following are a number of helpful points to remember when photographing from an aircraft.

1. Set the camera focus on infinity. Since virtually all aerial photographs will be taken at infinity, tape the focus ring at infinity before the aircraft leaves the ground. This will ensure that the focus is not accidently bumped during the excitement of volcano photography. Vinyl plastic electrical tape works well, as it is easily removed without breaking or leaving residue.

2. The shutter speed of the camera used in aerial photography should be at least 1/250 second, and preferably 1/500 or 1/1000 second. A slower shutter speed may induce motion, resulting in blurred photographs. Motion during exposure is one of the main problems of good aerial photography and is caused by the camera being hand-held, the forward speed and mechanical vibration of the aircraft, and the smoothness of flight relative to how much turbulence is in the air (Eastman Kodak Company, 1985, p.8). To reduce the effects of motion, use as fast a shutter speed as possible and keep the camera from touching the aircraft. Use a faster film instead of a slower shutter speed if the day is overcast (at CVO, 200 or 400 speed films are used on overcast days). To obtain a fast shutter speed with an automatic camera, use as fast a film as possible.

3. Shoot through open windows or remove the helicopter door before takeoff. Aircraft windows have distoring curves and hundreds of scratches, so that shooting through plastic windows severely limits the quality of the photographs. If possible, shoot through an open window or have the helicopter pilot remove the doors, thereby leaving an unobstructed view. If you must shoot through windows, hod the camera as close to and as perpendicular to the window as possible. This will minimize the possibility of unpleasant reflections from the windows. With auto-focusing cameras, shooting through an open window is a must, as many auto-focusing cameras may focus on the window instead of the volcano.

4. Keep airplane wings and helicopter blades out of the view. Photographs with airplane wings and helicopter blades are less pleasing than those without. Airplane wings and helicopter blades also can cause auto-focus cameras to focus on them instead of the view.

5. The location of the sun is an important factor when shooting aerial photographs. Aerial photographs taken with a sun angle of 20-30 degrees above the horizon are the most satisfactory (Hackman, 1967, p.B157); photographs taken when the sun is 10 degrees or less above the horizon produce long shadows. In areas of high relief, such as volcanic terrain, shadows of large topographic features often obscure too much of the area unless the sun is well above the horizon. This has proved to be a major problem when photographing Mount St. helens dome, as the crater wall casts its shadow on the dome during winter months, or early or late in the day. In the summer, photography taken at midday produces little shadow and shows almost no relief at all, making details harder to see.

Repeat Terrestrial Photography

Repeat terrestrial photographs are taken over a period of time from a permanent mark and are used to document long-term landscape change, such as biological (fig.20.6), erosional (fig.20.7), and geological (figs. 20.1, 20.8) development around volcanoes. Repeat photographs can also be combined into one composite diagram to illustrate years of cumulative landscape evolution (fig. 20.9). Since 1980, more than 100 repeat terrestrial photography stations (photo stations) have been established at Mount St. Helens and the other Cascades volcanoes.

Ideally, repeat terrestrial photographs are taken from the same point, using the same camera and lens (or at least the same camera format and focal-length lens), with the camera at the same height above the ground, and aimed in exactly the same direction. This results in the same photographic view each time. At Mount St. Helens, this goal has not been fully achieved. Many photo stations are sporadically visited by different people with different camera, lens, and film combinations, and who stand in slightly different locations. Harrison (1974, p.469) stated: "Retrieval of information from old photographs of geological features will be enhanced if the photographs are repeated from the same site. Reoccupying the exact site may not be essential, but it makes the interpretation of the photographs more convenient." What has resulted at CVO is a collection of photographs that are not all perfectly repeated views, yet nonetheless document changes around the volcano (fig. 20.7).

Figure 20.6: Two repeat photographs of Lassen Peak illustrate biological development occurring around volcanoes.
	Figure 20.6A: Lassen Peak after the May 22, 1915 blast. B.F. Loomis photograph, courtesy of the Loomis Museum Association, Mineral, California. Photo by B.F. Loomis, 1926.
	Figure 20.6B: Lassen Peak as viewed from the same location as A, 69 years after the blast. USGS Photo by Lyn Topinka, 1984.

Figure 20.7: Although taken from slightly different positions, two repeat photographs of the Upper Muddy River at Mount St. Helens illustrate erosional development around volcanoes.
	Figure 20.7A: October 1980, five months after the May 18, 1980, eruption.
	Figure 20.7B: The same are photographed in 1981, one year later.

Figure 20.8: Repeat photographs of Mount St. Helens lava dome illustrating the importance of choosing a correct focal-length lens.
	Figure 20.8A: In 1981, the dome was photographed using a standard 55-mm lens from a photo station approximately 1 kilometer away.
	Figure 20.8B: When photographed 4 years later, the dome had outgrown the field of view of the 55-mm lens.

When establishing or reoccupying a photo station, a number of ideas should be kept in mind:

1. Numerous photo stations should be established. According to Veatch (1969, p.51), "it is better to establish too many rather than too few photographic stations. Some stations can always be dropped, but once any photographic records are missed they are lost forever." Over the years at Mount St. Helens, many different photo stations have been established, often within sight of each other, but not all stations have survived. Some have been destroyed by volcanic activity and river channel migration; the locations of others have been forgotten. A few were established for short-term projects, occupied for a few days, weeks, months, or even years, and then abandoned when the project ended. Some stations have turned out to be good photo stations and have been reoccupied many times over the past 10 years, and others, while being visually and informationally good, have not been reoccupied consistently because of cost of difficulty of access.

   Figure 20.9: Composite diagram of dome growth, made from 6 years of repeat terrestrial photography, taken from a photo station approximately 1 kilometer north of the dome.

2. Each photo stations should be a permanent mark on the ground. Permanent marks should be established so photographers know exactly where to place the tripod to repeat the photographs. At Mount St. Helen, fence posts, steel towers, large rocks, bridge supports, established USGS bench marks, and, as a last resort, spots on the ground located a known number of paces from a permanent object have been used as permanent markers. During one dome-building episode, a short-term permanent mark was established using a 55-gallon drum as a camera mount (fig. 20.10). Long-term permanent marks at other Cascades volcanoes are often established CVO bench marks (fig. 20.11).

   Figure 20.10: A 55-gallon drum filled with rocks was used as a camera mount and a permanent mark for a short-term photo station. The drum was filled with rocks for stability, a tripod head was secured to the lid, and the camera's protective metal housing was attached to the tripod head.

3. Tripods are a must. A tripod facilitates aiming the camera, helps to ensure that the camera is correctly aligned over the permanent mark, and is necessary to maximize photo sharpness by reducing camera vibrations. Very few people can hold a camera sufficiently still during an exposure longer than 1/60 second. Camera movement results in blurry photographs. At CVO, Bogen 3020 "Professional" tripods with Bogen 3025 "3-D" or 3028 "Super 3-D" three-way-tilt heads are used. At other Cascades volcanoes, the staff photographer uses a Bogen 3058 "Super Pro" tripod with a 3047 "Deluxe" heavy-duty three-way-tilt pan head, or the head is mounted in the Kern tripod used in the deformation network (Iwatsubo and Swanson, chapter 10).

4. Take along a copy of the photo taken previously at the photo station to aid in exact framing of the same scene.

5. To ensure successful repeat photography, keep accurate notes on cameras and lenses used, film type, date and time, the height of the tripod, the angle of tilt of the camera if not level, and the azimuth of the camera. Record detailed descriptions on how to get to the photo site and how to identify the permanent mark. These will all be important when repeating the photograph at a later date. If the photo station cannot be reoccupied on a particular visit, note why.

6. Take a photograph of the camera setup at the photo station. This greatly facilitates reoccupying the exact site and is an invaluable aid to the next person sent to occupy the site. Many of the photo stations at other Cascades volcanoes are official U.S.Geological Survey bench marks that do not protrude above the surface of the ground. Photographs showing where the tripod is, with nearby rocks, vegetation, or outcrops visible (fig. 20.11), have saved considerable time when searching for the station.

   [figure not available]

   Figure 20.11: Tripod setup at South Sister volcano facilitates relocating the site years later. At South Sister, the same tripod is used for both the photo station and the deformation network's surveying instruments.

7. Shoot the scene with both color slide and b/w negative film, so that the same scene can be photographed in slide format for talks and shows and in b/w format for publications and historical archiving. Although b/w prints may be derived from color slides, then are inferior to a print from an original b/w negative and therefore not as desirable for historical purposes.

8. If possible, use the same focal-length lens each time a photo station is occupied. This helps to facilitate quick comparison of images without having to manipulate the photographs, but it is not absolutely necessary. According to Malde (1973, p. 198) "views made with cameras of different focal lengths from the same lens position will always match exactly, provided that both are printed and cropped to the same size." During eruptions and floods, however, there is no time to print and crop photographs. Also, when different people are reoccupying the photo stations, having one "project camera" available to give to the field crews results in more consistent photographs. For example, many CVO photo stations were established at cross-section survey points along the stream drainages. Repeat photography is shot upstream, downstream, and across the drainage while hand-holding the camera and standing at eh channel edge near the cross-section marker, or near the edge over the instrument stake. The field crews doing the surveying (and the photography) are seldom the same each time. By eliminating one variable, that of the different fields of view of different cameras and lenses, the resulting images have been easier for researchers to study later.

9. Lenses of different focal lengths should be used on the same subject at each photo station during each visit. Shooting a photo station at only one focal length might present irreversible difficulties in the future. On August 22, 1981, the dome was approximately 163 meters high and 400 meters wide when photographed from a station one kilometer north of the dome. The dome fit within the frame of the 35-mm camera using a standard 55-mm focal-length lens (fig. 20.8A). By August 12, 1985, the dome was 230 meters high and approximately 800 meters wide, and no longer fit in the frame (fig. 20.8B). Unfortunately, it was too late to capture the 1981 scene with the wider-angle 28-mm focal-length lens.

10. When possible, the photographs should be taken about the same time and date each year. "In this way, because the shadows and highlights are then faithfully reproduced, the old and new photographs can be better compared." (Rogers and others, 1984, p.xxvi). At Mount St. Helens this often is not possible; many of the photo stations are reoccupied only after eruptions or floods, regardless of the time of the year. Other photo stations visited several times a year offer better opportunities for getting photographs at nearly the same date and time.

11. If the weather or lighting conditions are not perfect, take the photograph anyway. Because film is inexpensive compared to the cost of getting to a photo station, a large number of photographs are taken at Mount St. Helens photo stations even if the weather or lighting conditions are not perfect. that way, if the station cannot be reoccupied during better conditions for some reason, at least something has been recorded. At the other Cascades volcanoes, photographs are always taken when a photo station is reoccupied because it may be years before we visit it again.

12. Consider the future. Try to imagine what the photo station will look like in the years to come. Will there be any small trees in the foreground that will one day grow up to block the view (fig. 20.6)? Is the station so close to the edge of an active channel that it may be eroded away? Is the station directly in the path of potential lahars, pyroclastic flows, or rock avalanches? If so, perhaps consider establishing another photo station in a more secure spot.

Illustrative Terrestrial Photography

Illustrative terrestrial photography is perhaps the most common photographic technique employed by scientists. Illustrative terrestrial photographs (figs. 20.2A, B, D, and 20.12) are taken from the ground of any subject, with no plans to ever reoccupy that exact photographic spot again, and with no other purpose except to document and illustrate some natural or man-made feature. Every year at Mount St. Helens hundreds of illustrative terrestrial photographs are taken of the crater, dome, drainage channels, erosion, rockfalls, returning plant life, scientific equipment, researchers at work, and other topics.

Occasionally place a "ruler" in the scene when photographing close-in subjects and include a recognizable object in the scene when photographing a distant subject. Measurements can be then calculated from the photograph, or at least a general idea of scale of the image can be obtained. Rock hammers, shovels, ice axes, camera lens caps, or film boxes are useful when photographing close-in subjects (fig. 10.12A), and fellow researchers, helicopters, and automobiles works well in wider views (fig. 20.12B).

Figure 20.12: "Rulers" help illustrate size in photographs.
	Figure 20.12A: Film box (circled) shows relative size of the boulder.
	Figure 20.12B: Two scientists (circled) show relative size of trees devastated on May 18, 1980.

Time-Lapse Photography

Time-lapse photography is another technique useful when photographing volcanoes. For purposes of this report, time-lapse photography is defined as repeat terrestrial photography taken in a short period of time with programmable cameras. The cameras are programmed to photograph an important geologic or hydrologic event by shooting a roll of film in predetermined time intervals. At Mount St. Helens, time-lapse photography has been successfully used to photograph dome growth during dome-building episodes and debris flows originating at Shoestring Glacier.

In August 1982, an 8-mm Eumig movie camera, modified for time-lapse, was installed at a photo station approximately 1 kilometer from the dome and used to photograph an emerging lava lobe. A frame was shot every 5 minutes, resulting in nearly 5 days of lobe growth condensed on one 50-ft roll of film. In October 1986, the cameras was placed on top of the dome and aimed at an actively extruding lobe. The camera was programmed to shoot a frame every 10 seconds, resulting in a roll of spectacular footage of the lobe's active spreading center.

Minolta X700 cameras with programmable data backs were also used during the same two eruptive episodes. On August 19, 1982, a camera was mounted in a protective housing and set on a tripod approximately 0.5 kilometers north of the dome. Throughout the next two days, five rolls of film were shot, at different time intervals. The site was then reoccupied and photographed sporadically during the next two weeks. Figure 20.13A shows tracings of the August 19 lava lobe taken from time-lapse frames, and figure 20.13B shows tracings of the new lobe on August 19 and 20 and September 1.

Figure 20.13 Between August 19 and September 1, 1982, a 35-mm time-lapse programmable camera was used to photograph dome growth. Resulting photographs were later used to sketch the growth.

On October 21, 1986, two Minolta X700's were installed 8 kilometers north of the dome in an attempt to photograph the predicted emergence of a new lobe during the night. One camera was programmed to take an exposure 10 minutes long every 2 hours, and the other camera was programmed to take a 20-minute exposure every hour. A 20-minute exposure taken at 0500 hours (local time) the morning of October 22 shows no hint of a glowing lobe while the next frame taken at 0600 hours clearly shows glow from a hot dome. The camera documented the emergence of the lobe, consistent with the interpretation of seismic records (Elliot Endo, oral commun., 1986). The next night, October 22, the cameras were programmed to take 30-minute exposures of the new lobe (fig. 20.14).

Figure 20.14: A programmable 35-mm time-lapse camera was used to shoot this 30-minute evening exposure of the October 22, 1986, dome growth, resulting in this moonlit view of a 15-hour-old lobe.

In 1981-83, the Minolta X700 camera was also used to photograph sequences of debris flows originating from Shoestring Glacier. The camera's motor drive was set to shoot 3.5 frames per second when remotely triggered by an infrared beam (Tom Pierson, oral commun., 1990). This setup was successful three times.

Time-lapse cameras left at photo stations create a new set of photographic problems. Rain, snow, ice, and ash can coat camera lenses or housing windows, clouds can obscure views, wind can blow cameras over, and eruptions, lahars, or floods can destroy cameras. Camera batteries can die with no warning; cold weather is the major reason for the failures. Numerous attempts at photographing emerging lobes on the dome have been ruined by blowing ash during the summer, cold, snow, and ice during the winter, and clouds obscuring the view at all times during the year. Attempts to photograph drainage-channel development during major storms have been unsuccessful due to wind and rain. One of the Eumig 8-mm movie cameras was swept away at Mount Rainier during a glacial outburst flood.

To ensure the best possible chances of obtaining good time-lapse volcano photography, mount the cameras at secure locations in environmentally sealed camera housings, keep the cameras warm during colder months, and provide enough power to keep the system running. At Mount St. Helens, an unheated plexiglass box and an unheated metal box with an inset glass window (fig. 20.10) are used to protect the Minolta X700's. The Eumig movie cameras have their own weatherproof housings, which still needed to be sealed with duct tape to prevent blowing ash from entering the system (fig.20.15). All cameras are generally mounted low to the ground, and rocks or sandbags are placed around them to provide stability in winds (which can exceed 100 kilometers per hour). Although the Eumig movie cameras have not been heated, they have usually remained running even during the winter. Ice quite often forms on them, however, making the footage unusable. The Eumigs run on one 6-volt "lantern" battery, and the cameras have been modified to accept a parallel battery setup. The Minolta X700's will not stay running during periods of cold, and they have not been modified to accept parallel batteries. In the warmth, at 20 degrees C, one lithium battery (3 volts) will operate a Minolta X700 for approximately 6 hours of exposure time.

The Minolta X700's used to photograph the night scene of the growing new lobe (fig. 20.14) were mounted in an unheated observation building, with camera ports cut into the walls. Winter temperatures in the building have been recorded as low as -15 degrees C, necessitating an inexpensive method to keep the cameras ward. A camera-heating system using electric socks (such as those worn by hunters and fishermen) was devised. Electric socks have a heating element sewn into the sock toe and are powered by a 1.5-volt "D"-cell battery. The socks are modified to accept up to four batteries in parallel, therefore providing over 30 hours of heat. Two socks are used per camera. The socks are turned inside-out and the heating elements placed next to the camera, data back, and motor-drive batteries. The rest of the sock is then wrapped around the camera to provide extra insulation, and the entire system is covered with waterproof nylon. Only the front of the camera lens is exposed.

Quantatative Measurements

The capability to make quantitative measurements from photographs is an important application of photography. The researchers at CVO have used this capability extensively with vertical aerial photography and occasionally with terrestrial or oblique aerial photography. the dimensions of the dome (Swanson and others, 1987) are routinely calculated with the help of photographs.

Quantitative measurements and calculations are based on four variables: h, the subject size; h', the image size (size of the subject as measured on the negative or transparency); F, the lens focal length; and v, the lens-to-subject distance (Blaker, 1976, p.343). Their relationship is

          h'/F = h/v

This formula can be used not only for obtaining measurements from photographs but also to determine what focal-length lens is needed, or how far away a photo station must be from a subject in order to have that subject fill the frame.

Measurements are usually obtained from large-format vertical aerial photographs. The lens focal length and lens-to-subject distance (altitude of the aircraft above the ground surface) are routinely recorded, image size is easily measured off the large negative or transparency, and subject size is then computed. Image size can also be determined from photographic prints if the relationship is know between the print and the original negative or transparency (amount of enlargement or reduction). Image size is then calculated as if measured from the negative or transparency.

If the scale of a vertical aerial photograph is known, two variables can be deduced. Since scale is represented as a ratio against 1, the image size (h') is the "1", and the subject size (h) is the other number. If either the altitude of the aircraft or the focal length of the lens is known, the remaining variable can then be solved for. This is useful in determining at what altitude the aircraft should fly to obtain the desired scale. If a 1:10,000-scale photograph of the dome is desired and the camera has a 152-mm (6-inch) lens, the aircraft will need to fly approximately 1.5 km (5,000 feet) above the top of the dome to obtain the desired scale

          1/152 = 10,000/v = 1,520,000 mm = 1.5 km

Measurements can also be obtained from oblique aerial or terrestrial photography, although the process is more difficult and not as exact. In an oblique photo the distances in the photo generally increase from the bottom (nearest the camera) to the top (farthest from the camera), thus making it difficult to calculate subject size. Image size is readily obtainable from the negatives or transparencies, and lens focal length should be written in the notes. Unfortunately, both the subject size and the lens-to-subject distance are variable across the film and are often unknown. One of these needs to be obtained to complete the equation.

An easy method to obtain lens-to-subject distance for terrestrial photography calculations is to measure the distance between the photo station and the subject using topographic maps or vertical photography. Another method is to use surveying equipment and accurately measure the distance from the camera to the subject. When surveying cannot be done, rough estimates of the lens-to-subject distance can be make if the distances of at least two known objects (control points) roughly in the same plane as the main subject are obtained. The distance to the original subject can then be estimated geometrically between the control points. The equation can also be solved if the subject size or the control-point sizes are known or can be measured or estimated, leaving the lens-to-subject distance to be calculated. The surveying or measuring of the control points does not have to be done when the photo station is initially established and it does not have to be done each time a photograph is taken, so long as it is completed sometime during the life of the photo station (Malde, 1973, p.197).

Once the distances to, or sizes of the control points are known, distances and sizes of many features within any photograph taken from that photo station can be calculated, although the exactness of the calculations depends on the number and location of the control points. The greater the number of control points measured, the more exact will be the calculated subject size. Approximate size can still be determined if only one control point is available and often this rough estimate is all that is needed to help illustrate an idea. For example, on April 16, 1983, 35-mm photography from a photo station was used to calculate the rate of rise of a small plume of steam and ash (fig. 20.16). This particular photo station was chosen because of its location of approximately the same elevation as the dome, thus offering a nearly perpendicular view of the dome providing one known control point. The photo station was also close enough to be able to measure the plume images on 35-mm film, yet far enough away to minimize the effect of varying distances between the plumes and the camera. A Minolta X700 camera with motor drive and data back was programmed to shoot a picture every 5 seconds and was manually turned on at the first sign of a plume. For this situation, the focal length of the lens was known, the image size was measured from each frame. The lens-to-subject distance of the "center-of-dome" control point was measured from topographic maps. The unknown variable, the height of the plume, was then calculated and the rate of rise was plotted.

Figure 20.16: Two minutes of time-lapse photography help illustrate the rate of rise of a small plume of steam and ash.
	Figure 20.16A: Height of rising plume sketched and calculated from oblique photographs.
	Figure 20.16B: Plume height plotted against time.

Conclusions

Personnel of the Cascades Volcano Observatory have used a variety of cameras and techniques to document changes and events at Mount St. Helens and other Cascades volcanoes. The selection of camera equipment has been largely decided by scientific need, budget limitations, and personal preference. Still photography, especially small-format, has been used most extensively, while video and movie photography has been underutilized. A variety of techniques has been used involving aerial and terrestrial photography, and numerous photo stations have been established. Use of photographic products include illustrations for publications, transparencies for slide shows, maps made from vertical aerial photography, and diagrams made from repeat terrestrial or time-lapse photography. We have learned that photography in any form is better than no photography at all.

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