Ecological Damage from Natural Events - Geological Evens - Lecture Note - Completely Remote Sensing tutorial, GPS, and GIS -
Ecological Damage from Natural Events - Geological Evens

Natural catastrophes of a direct geologic nature, such as volcanic eruptions and earthquakes, are a much feared and often unavoidable calamity to people living in proximity. Although hurricanes have caused damage into the many $billions, potentially a major earthquake in a metropolitan area such as Los Angeles can be even more costly. We will review how remote sensing contributes to monitoring pre-event conditions and assessing post-event damage on this page.

Most of the page will be devoted to one event that has captured the American imagination and still leads to fears and concerns about repetitions. This is the major eruption at Mt. St. Helens in Washington State in May of 1980. We will go into enough detail to qualify this page as a Case Study.

Mt. St. Helens (to which we will usually refer hereafter as MSH) is part of the Pacific Ring of Fire, where stratovolcanos of (most commonly andesite-dacite composition) form on the upper tectonic plate at a subduction zone, as indicated in this diagram, which suggests that frictional heat during the underthrusting causes melting that rises upward as magma and, if the melt reaches the surface, as volcanic structures whose repeated eruptions over millions of years leads to the distinctive cones that are among the most impressive of all mountains.

Subduction of the Juan de Fuca plate under Oregon-Washington, responsible for Mt. St. Helens.

MSH is one of the major volcanic cones making up the Cascades that start in Northern California and continue just into British Columbia. The volcanoes are a direct and normal consequence of classic subduction, in this case of the small Juan de Fuca plate caught between the Pacific and North American plate. These volocanoes are shown in this map:

Map of Cascadian volcanoes.

Until 1980 there have been no major eruptions of the Cascadian volcanoes since colonial times. MSH last erupted about 4000 years ago. Mt. Hood, Mt. Rainier, and several others have erupted in the last 10000 years. Mt. Lassen had a small eruption in 1915.

MSH lies to the west of the main line of stratocones, as shown in this 1973 Landsat image.

Mt. St. Helens (near center top) to the west of Mt Adams, in a Landsat 1973 image; note the heavy forestation in most of the region.

MSH had always been praised as one of the most "handsome" stratocones in the Cascadian chain - some considered it comparable to Mt. Fujiyama in symmetrical beauty. Below is a ground photo and an aerial photo of this mountain, which in pre-1980 times reached an altitude of 2970 m (about 9800 ft) above sealevel.

Ground view of Mt. St. Helens
Aerial photo of Mt. St. Helens.

Although MSH had undergone several minor steam and ash explosions in the 1800s, it was considered by most volcanologists to be inactive or at least quasi-dormant. But in March of 1980, seismic records showed a marked increase in small magnitude (3 to 4) earthquakes, and some steam venting. Thermal measurements suggested a near surface warming. An old, small dome near its top began to rise an average of 1-2 m per day. Volcanologists interpreted these signs as indications of some moderate level activity that might occur that year.

The bulge near the top of MSH in April 1980; this was a reactivation of the long-standing Great Rock Dome.

The majority opinion of those at the Cascades Volcanological Observatory (CVO) favored only insignificant activities with a low likelihood of any dramatic eruption. However, in mid-May a warning was issued for voluntary evacuation of the region around the volcano as a precaution. Many campers, and the soon-to-be famous Harry Truman (yes, that was his name) of Spirit Lake, ignored this since it was not mandatory. There was a brave hero, trapped in the advancing lateral blast: Dr. David Johnston of the USGS was a forward observer who radioed what he was seeing until buried by the debris. The U.S. Geological Survey had several other observers stationed near the volcano on Sunday morning, May 18, 1980, and a light aircraft was circling the structure at that time.

Before documenting individual stages, we will describe narratively the sequence of the first minutes of eruption, using these two diagrams and suggesting that the reader examine the table at this CVO website.
Diagram depicting the main stages of eruption at Mt. St. Helens.
Another, somewhat simpler eruption diagram for the MSH event.

The ground around Great Rock Dome failed first, followed quickly by detachment of rock below it as a debris avalanche of blocks up to house size. This released interior pressure which expelled material as a lateral blast and a surge of ash, blocks, gases, and steam that moved northward at speeds up to 1000 km/hr. The surge moved indiscriminantly over rough terrain out to 12 km, carrying debris for the next 30 seconds into the North Toutle River and covering part of Spirit Lake (which retains both the body and spirit of Harry Truman). Air overpressures flattened trees up to 18 km from MSH's peak. Over the next ten minutes the mountain, after being lowered 400 m to form a huge ampitheater (much like a breached crater) 2 by 3 km wide and 680 m deep, continued to expel tephra (ash and pumice) mostly vertically up to an altitude of 18 km where winds carried the fine-sized particles for great distances to eventually reach the ground as ashfall. On the first day much of the ash mixed with melted snow to produce lahars (volcanic-particle mudflows), some being channeled into rivers, choking them for many miles. Pyroclastic flows continued intermittently for days, along with vented steam that mixed with this ash to generate more mudflows carried into the North and South Forks of the Toutle River. We shall document these actions in illustrations below.

The blast in particular was fatal to 57 people nearby. All said, 540,000,000 tons of ash came to rest over 55000 km2. Ash beyond MSH reached locally up to a meter thick and to a few centimeters in Yakima, Moses Lake, and other towns in central Washington. Small eruptions continued through July 1980 (the writer and family reached the area in June but missed seeing any of these events) and sporadically through 1986. MSH, having done more than $1,000,000,000 in damage, quickly became a major tourist attraction in the Pacific Northwest.

Now, let us document visually much of what was described above. We start, for reference, with a map produced by the U.S. Geological Survey, of the MSH area, showing the major deposit types:

Map showing the principal types of deposits at MSH.

The great eruption began at 8:32 AM {PDT), probably triggered by a 5.1 magnitude earthquake, causing an abrupt failure around the bulge, as it seemed to tear loose into the debris avalanche, even as the first ash was expelled from the peak, a moment captured on film.

Activity affecting the bulge on MSH just at the moment of the start of the eruption; the material on the move is the beginning of the debris avalanche.

Only a few seconds later, we see the lateral blast as it blew out the side of the mountain, initiating the collapse of the peak.

The beginning of the lateral blast

The effects of that blast were widespread, causing trees to be stripped of branches and closer in uprooted to lie prone on the ground.

Trees downed by the MSH air blast.

The next pair of images focus on the modification of the ash and debris into what is called in its French terminology a "nuees ardente" or "glowing avalanche". A synonym is "pyroclastic flow" - entrained tephra (the clastic particulates such as ash and pumice) propelled and supported by steam and other gases - that moves downslope under the influence of gravity. This is an airborne avalanche of hot, thick volcanic debris composed, in the case of MSH, of material from the escaping lava mixed with now fragmented parts of the pre-blast volcano wall.

Pyroclasic flow looking downward from an aircraft that was near MSH at the time of eruption
A  pyroclastic flow seen from the ground.

This post-eruptive photo shows some of the components present in a pyroclastic flow at MSH:

Pyroclastic flow which included large blocks of pumice

Over the next 10 minutes, MSH sent ash vertically by means of thermal uplift of heated gases into a plume that rose to a height of 18 km before starting to disperse downwind. One of the most famed photos taken of this is shown here. (The picture is hanging in my study just to the right of the computer desk; I have seen it attributed to Austin Post or to Robert Kimmel). Note the dark flows which are not lava but mudflows (see below):

The vertical eruptive plume of MSH

The plume continued to rise throughout the day. This next photo, in color, shows the curtain of falling ash as highlighted by the sunset glow.

The ash plume of Mt. St. Helens, photographed in sunset light.

The ash was widely dispersed, mainly to the east, as shown in this ashfall map.

Map of disperse ash from MSH.

Another map shows the thickness (isopach map) of the main lobe of ash.

Ashfall thickness map for the 1980 MSH eruption.

Streets and lawns in towns east of MSG, such as Yakima, received up to 6 cm of ash, that was removed from roadways, as shown here, but eventually was washed away by rain or carried into the soil.

Tractor scraper removing ash from a neighborhood street.

Looking from north to south towards MSH, the nature of the debris avalanche deposits is evident from this ground photo

Debris avalanche deposits from the 1980 MSH eruption.

Deposits in the debris avalanche zone were hummocky and often in layers containing coarse boulders and smaller blocks:

Surface showing the terrain produced by a debris avalanche
Layered tephra - mostly of large blocky fragments - had this appearance from the ground near the volcano:
Layered ash from a pyroclastic flow deposit.

Mudflows (lahars) began to develop on MSH almost from the beginning and continued (occasionally) for years. The mudflow deposits can be both dark and light-toned.This photo shows a dark mudflow that happened in 1982

Dark mudflow developed from the interior of the MSH ampitheater in 1982.

A light-colored ash flow that has entered a stream valley appears from above:

Light ash deposited in a stream valley.

The North Toutle River was choked with ash debris and lahar deposits:

The Toutle River filled with lahar deposits.

Upstream the lahars carried logs (precut at a timber mill) that jammed against a highway bridge. Beset by further mudflows and lahars this bridge was eventually crushed and buried.

Logs jammed against a bridge across the North Toutle River.
The bridge is destroyed.

Further downstream another bridge survived:

A bridge across Highway 99 not destroyed by the debris and lahar flows filling the Toutle River.

Subsequent rain runoff has brought water into the Toutle River, causing stream dissection that produces channels.

Dissected mudflow deposits in the Toutle River.

Let us return to the center of the ampitheater where most of the volcanic activity was concentrated between 1980 and today. After the blowaway of the upper mountain, thick lava re-entered the crater floor as deposits that once more established a central dome composed of dacite (quartz-bearing andesite). A July 1980 view shows this dome; below it is a much more recent photo which indicates how much bigger the dome has grown:

The central dacite dome in July 1980
The dome in the late 1990s.

Two diagrams depict dome growth: the upper covers the period from 1980 through 1983 while the lower diagram extends this to 1986.


The dome now is about 300 meters higher than its starting height and covers more than two kilometers at its base.

Before we turn to the role of remote sensing in monitoring MSH, let us take two more views of the post-1980 mountain. The first image was taken from the rim looking down into the ampitheater, the dome, the debris and pyroclastic deposits, partially exposed Spirit Lake, and the massive Mt. Rainier to the north. The second looks at the mountain from the south, where no obvious signs of an eruption are evident except for the loss of the peak.

View from the rim of MSH looking into the ampitheater and beyond.
Mt. St. Helens seen from the forest to its south.

Since the full force behind the 1980 eruption was directed northward, one would expect a near absence of deposits and other signs on this south side. However, field work has found some much older deposits from pervious eruptions of Mt. St. Helens that resemble debris avalanche deposits formed in 1980.

Pre-1980 (probably thousands of years old) volcanic deposits in areas to the south of  Mt. St. Helens.

As you would expect, the eruption and its after effects can be effectively monitored with remote sensing tools by various satellites and aircraft. Just a month and a half after the May 18, 1980 eruption, a cloud-free Landsat-3 image was obtained that showed the depositional pattern.

Part of a Landsat MSS image taken on July 31, 1980 that shows the region of SW Washington State, with the destruction caused by MSH clearly displayed.

As soon as a computer-compatible tape (CCT) was made available to the writer (NMS), I and a colleague (Charles Bohn) worked well into the night on the IDIMS image processor at Goddard to obtain this next classification map. Compare the main features shown in different color, which we did not categorize at the time because of lack of familiarity with the category names now used, with those shown in the deposits map shown above. This exercise verifies that with computerized data of this nature, one can produce meaningful interpretations in a very short time.

Geologic units in the Mt. St. Helens eruption deposits mapped using a simplified computer classification program available to the writer at NASA Goddard.

Landsat imagery combined with DEM data produces this perspective (oblique or side-looking) view of Mt. St. Helens (middle center) and its surroundings; the red color helps to define areas of heavy ash fall now undergoing regrowth.

Perspective view, looking south, of Mt. St. Helens after the eruption, made from a Landsat image registered to DEM topographic data.

Compare the above perspective view made in the 1980s with this late 1980s version made using SRTM elevation data derived from two radar bands. The view here is to the southeast.

Perspective view of Mount St. Helens, with Mt Adams and Mt. Hood in the background, made from SRTM data acquired in the lat 1980s.

The central area of the excavated (blown-out) part of Mt. St. Helens, especially the extruded dome, remains hotter than its surroundings, as shown in this late 1980s thermal image made by the airborne TIMS instrument (see Section 9):

The partial crater (where the top was blown out after collapse) of Mt. St. Helens imaged by the Thermal Infrared Multispectral Spectrometer (TIMS); red denote warmest areas.

Repetitive Landsat coverage of MSH over the years has indicated that grasses and trees have gradually gained a foothold so that reforestation and other vegetative recovery is underway. These three Landsat images (1973; 1983; 1988) illustrate that:

Landsat views of MSH taken during three different years.

Ground photos taken in 1983 and 1998 at nearly the same scene show how trees have reestablished in the outer parts of the volcanic deposits, with ash apparently having decayed to early stages of soils.

8 9

The gradual plant regrowth in the ash deposits around the site has been followed over the years in Landsat imagery. Below we show a Landsat TM natural color subscene taken in August 1999. Although the gray ash is still widespread and dominant, careful inspection indicates various shades of green within the deposits where trees, bushes, and even grasses have made a substantial comeback in the two decades since eruption.

Landsat-7 natural color subscene of southern Washington State, taken in August of 1999, featuring the blown top (crater) of Mount St. Helens and surrounding ash deposits, parts of which now shown green coloration ascribed to gradual restoration of arboreal vegetation and brushlands in the devastated areas; north at top.

One of the last photos taken on October 1, 2004, by the astronauts on the International Space Station does not capture the still limited extent to which vegetation is returning to MSH. This photo is in near natural color:

October 1, 2004 digital photo taken by an astronaut on the ISS of the Mt. St. Helens area.

By no means has MSH gone dormant. Minor but notable eruptions were occasional in the '80s. Until 2004 that activity subsided to some degree. But watchful eyes of experts, mainly those at the Johnston Cascades Volcano Observatory, are using many tools to monitor this and other volcanoes in the chain for signs of impending eruptions. The main monitoring approaches can be accessed at the USGS's CVO site. One example: GPS is being used on the volcano to measure any vertical displacements on the volcano's flanks or within the ampitheater.

Geologist using GPS to monitor Mt. St. Helens.

In September of 2004 there was a dramatic increase in the number of small earthquakes from beneath MSH's surface.

Plot of earthquake frequency at MSH in 2003-2004.


Here are seismograms typical of this flurry of activity:

The seismic record for one earthquake event at Mt St. Helens.

During this period, the dacite dome has risen about 30 meters, as shown in this aerial view.

The dacite dome at MSH in September, 2004.

An airborne flight of the TIMS (thermal) instrument over MSH show in the left image hot areas in red and cold snow as blue. Other hot areas as appear as light tones in the right black and white image.

Thermal images of MSH in September, 2004

As September, 2004 progressed, ash and steam began to exude in significant amounts, leading the CVO to issue a Level 3 alert (strong likelihood of an eruptive event of moderate magnitude).

Ash and steam from MSH's central dome
A large ash cloud from MSH in late September.

An especially esthetic eruption occurred at sunrise on October 10, 2004:

Steam and some ash in a vented cloud from MDH at sunrise on October 10, 2004.

By mid-October, magma had reached the surface in the ampitheater (thus, to use correct terminology, it is now lava). A new smaller but rapidly growing dome, just south of the main dome, has been forming. Here are twp AP photos of the new dome in the day (left) and at night (right) in which the red glow is emerging lava.

The newly forming lava dome at Mt. St. Helens; AP photo The new lava dome at night; AP photos

A closer view taken from an airplane shows the new dome in its early growth stage on October 1. The label "glacier" is misleading; it is actually a large patch of snow. Below the aerial view is an IKONOS image of the now paired domes as seen from space.

Aerial view of the growing lava dome at MSH>
IKONOS image of the two domes in the MSH ampitheater.

A lidar altimeter instrument was flown over the amphitheater to measure upward elevation changes due to the upwelling magma. These are plotted on an IKONOS image as the frame of reference. Color code for elevation increases: Blue = 0.1 to 3 meters; Green = 1.5 to 40 m; Yellow = 40 to 80 m; Orange = 80-120 m.

Lidar measurements of the rising surface of the MSH ampitheater; see text above for color-coding of elevation increases.

An aircraft thermal remote sensor, called MASTER (using components found on the MODIS and ASTER sensors on the Terra spacecraft), was flown over MSH to show the lava hot spots in detail:

MASTER images of the new dome at MSH; the one on the left shows both snow and smoke in blue.

Since its eruption MSH seems to have calmed down but some small earthquakes and a few steam clouds indicate possible activity in the foreseeable future. A good source to check out for updates on any MSH situation is the CVO Home Page.

Alaska's Aleutian Islands are a continuous chain of active to dormant volcanoes lying in the upper plate side of a major subduction zone. On August 8, 2008 one of the westernmost Aleutians, the 2.5 km wide Kasatochi Island, erupted, sending a major ash plume south and east, causing airplanes to avoid the area for more than 24 hours (ash can clog both prop and jet engines):

The volcanic island of Kasatochi, in a dormant state; ASTER image.
Kasatochi's August 2008 ash plume; the OMI (Ozone Monitoring Instrument) on the Aura satellite.

Just a few more examples of destructive volcanic events that were monitored by remote sensing. Overseas, at least one major eruption affecting populations seems to occur every few years. Currently considered one of the most dangerous in the world is Nyiragongo in the easternmost edge of the Democratic Republic of the Congo in the African Rift valley (see page 3-2).

Location of Nyiragongo.

Its "sister" volcano, Nyamuragira, centers about 20 km to the north. To the south is Lake Kiva, above which lies the city of Goma, in normal times with about 500000 people. Nyiragongo is a stratocone, with lavas containing high amounts of alkaline elements (sodium; potassium). The lava has remarkably low viscosity, traveling as fast as 100 km/hr (62 mph), which means it can descend on Goma and nearby villages in minutes. The top of the volcano collapsed in the past, producing a large caldera. This is evident in the ground photo that makes Nyiragongo look as though it has a flat top (this summit is 3400 m [11370 ft] above sealevel):

Ground view of Nyiragongo.

This SIR-C radar image of the Nyiragongo region shows this volcano and its "sister"

Radar image of the Nyiragongo and Nyamuragira volcanoes and associated lava flows.

The two volcanoes appear in this radar/DEM SIR-C perspective image:

Perspective view of the Nyiragongo (right) and Nyamuragira volcanoes.

Nyiragongo is one of the most active volcanoes in the East African Rift. It has erupted, mainly by expelling lavas from the caldera and from fissures beyond the rim, at least twice in almost every century since records have been kept. The last eruptions occurred in 1948, 1977, and 2002. The eruption on January 17, 2002 caused lava to descend the volcano's south flank so that within 3 days it had flowed through Goma, destroying much property and killing more than 600 people.

MODIS image of the 2002 Nyiragongo eruption.

That wide stream of lava was imaged by ASTER on Terra. The view below uses a Landsat TM image as the general picture, superimposed on which is this lava flow.

Landsat/ASTER image of the lava flow reaching Gova during the January 2002 eruption of Nyiragongo.

Parts of the town were covered with meters-thick lava, as seen here:

Lava filling a street in Gova, in the Congo.

The volcano continues to show threatening activity, as seen in this photo into the caldera center, with a red hot lava lake.

The current lava lake in Nyiragongo.

Volcanologists now consider Nyiragongo to be a strong threat for a major eruption in the next several decades. The dilemma facing the Congolese government and the Goma officials is whether to evacuate the city in the near future or await more conclusive signs of an impending eruption.

The June 15, 1991, event at Mt. Pinatubo on the island of Luzon in the Philippines is a classic example of an awakening volcano, portending eruption. After almost 600 years of dormancy, earthquakes around it began in April of 1991. Their increase prompted evacuation of more than 50,000 people. Just three hours before the main eruption, the AVHRR on NOAA 7 imaged the billowing clouds of water vapor mixed with ash, that foretold the impending climax. This three-band color composite shows the eruption material interspersed with clouds associated with Typhoon Yunya (left image).

AVHHR image of Mt. Pinatubo, Phillipines, shortly before the June 15, 1991 eruption.
 Photograph of the Mt. Pinatubo eruption.

The peak eruption (right image), of the violent Plinian type, sent pumice, ash, and chemical aerosols above 12,200 m (40,000+ ft), leaving behind a 2 km (1.2 mile) wide caldera (cavity) that displaced most of the summit. Sulphuric acid was a major constituent of the aerosols that spread worldwide, affecting the weather and climate for the next five years. In the immediate vicinity, ash deposits surrounded the volcano for 20 km, destroying most of the heavy forests. That is evident in this before and after pair of images, obtained by the Multispectral Electronic Self-Scanning Radiometer (MESSR) on the Japanese MOS (Marine Observation Satellite) operated by NASDA (National Space Development Agency, of Japan).

 Before and after images made by the MESSR instrument on the Japanese MOS satellite; in the after (right) image, ash is shown in pinkish-red.

3-15: What is the broad area of pink in the "after" image? ANSWER

Europe's most active volcano, Mount Etna in the northeast corner of Sicily, began a series of strong eruptions in mid-July of 2001. Lava flows (dark red) threatened villages perched astride this stratovolcano's slope. One of its more violent eruptions was captured by a sensor on the Terra spacecraft, as seen in this image:

July 2001 Eruption of Mount Etna in Sicily.

This is all we wish to say about Mt Etna now, since it will be the subject of page 13-4d which will summarize the "multi" concept.

The most active volcanic area in the world is the Kilauea rift on the east flank of Mauna Loa on the big island of Hawaii (see page 17-3 and page 9-7). A more or less continuous period of eruptions of basaltic lava began in 1983. Lava has moved off island into the ocean at several points of entry, in effect building on to the land. Landsat-7's ETM+ sensor captured these two images (top, natural color in the visible; the bottom, a thermal image processed to show the warm residual heat in the lava as a red tone). While the paths and progress of lava (typically, 300,000 to as much as 600,000 cubic meters/day when active) are closely followed by park rangers and volcanologists on the ground (thus permitting early warnings to villagers that a lava stream may come their way), the space imagery give a long term running account of the spread of lava over the years.

Visible (top) and thermal (bottom) images of the Kilauea lava flows, seen on May 23, 2000 by Landsat-7

Mud flows often accompany volcanic eruptions. These, and landslides, also occur after heavy rains. A landslide/flow is depicted in detail by the IKONOS satellite for an area in Venezuela subjected to a deluge and subsequent flooding.

IKONOS image showing a fluid landslide moving through a small village.

Landslides are common by-products of ground shaking resulting from earthquakes. A 7.2 magnitude quake occurred in Pakistan on October 8, 2005, causing perhaps as many as 70000 fatalities in that country's north near Kashmir and parts of neighboring India and Afghanistan. Space Imaging's IKONOS has acquired images of the damage. In the town of Muzzaffarabad, a landslide removed part of a mountain slope carrying the debris into a river. The area moved is dark in the lower image but the upper image now shows a light-toned scar.

Par of Muzzaffarabad in northern Pakistan; lower image is pre-earthquake; upper image shows the landslide scar and the muddy river water choked with debris loosened by the October 8, 2005 earthquake.

Turning now to a direct accounting of the effects from earthquakes. Considerable scientific manpower and money have been dedicated to discovering ways to predicting damaging and life-threatening natural events - mostly of a geologic nature. Earthquakes and volcanic eruptions lead the list. Radar interferometry (see page 11-10) offers real promise since one of its accomplishments is to be able to measure vertical ground displacements (such as occur when a volcano begins to swell upwards and outwards as its magma chamber fills) and, under appropriate circumstances, lateral (subhorizontal) displacements (as occurs along strike-slip or wrench faults). In the illustration below is evidence of ground swelling at four volcanic sites in South America as determined by analysis of 8 years of data from the radar on ERS-1 and ERS-2; while this may not guarantee an impending eruption, it does fit the pattern known to foretell many eruptions.

Radar interferometric patterns that can be quantified to indicate upwards displacements, as noted at four volcanoes in northern Chile; this investigation using ERS data was conducted by Mark Simons and Matt Pritchard of CalTech.

As one might expect, high resolution space imagery can be effective in assessing earthquake damage. On December 26, 2003 a magnitude 6.5 quake occurred near the city of Bam, in southeast Iran. This ancient city's buildings are constructed mostly from sun-dried clay blocks. Many of these, poorly suited to withstand earthquake waves, failed catastrophically during the main temblor and subsequent aftershocks. Casualties in the town and surrounding areas have exceeded 36000 and may reach 50000 when all debris has been searched through (another quake in northwest Iran killed 50000 on June 21, 1990). This IKONOS image gives an idea of the destruction in Bam, in which >80% of the buildings in this metropolitan area (about 80000 lived in Bam and another 100,000 in nearby areas) were destroyed:

Part of Bam, Iran seen in a section extracted from an IKONOS image, in which the destruction is manifested by failed roofs, and often walls, the the mud brick homes that dominate the dwellings in that city.

This aerial view zeroes in on the nature of the damage:

Aerial photo of extent of damage in Bam, Iran from a devastating earthquake.

Surviving the destruction was the Citadel in Bam, the largest adobe structure in the world, seen here in a pre-earthquake image.

This next pair of MISR (Terra) images reveals another subtle manifestation of the aftermath of an earthquake of magnitude 7.7. This, the Gujarit quake which killed more than 20000 people, took place on January 26, 2001 along an active fault line in western India. This arcuate trace just above the large white sand area on the right is visible in both the January 15 and January 31, 2001 images. Look closely at that line in the Jan. 31 image, along its left half. Small black blotches are evident - these are not present in the Jan. 15 image. They are the marks of saturated soils resulting from liquefaction releasing groundwater that seeped to the surface after the earthquake.

MISR images of an area in western India; top was pre-earthquake; bottom is post-earthquake - note black spots (water) along the western trace of the fault line.

The largest number of countable human deaths from an earthquake, as occurred on land near the epicenter, in the last hundred years was approximately 242000 near and in Tangshan in Eastern China. However, the submarine earthquake (magnitude 9.3, the second largest on record) off the northern Sumatra coast on December 26, 2004 (see second page of Overview) may have killed more. The deaths were caused almost exclusively by tsunamis (huge "tidal" waves produced by upheaval of ocean water above the epicenter). By mid-January, 2005 official estimates placed the dead at ~140,000 but as the Indonesian government compared the accounted-for living with census figures, they have claimed by March that the total was much greater, approaching 300,000 (includes Thailand, India, Sri Lanka, and other countries around the Indian Ocean). The areas affected in and beyond the Indian Ocean are shown in red on this map (note that there was a nearby smaller earthquake several days earlier).

Map of the Asian and African coastlines that experienced the Dec. 26, 2004 tsunami.

Radar aboard a NOAA satellite provided data that displayed upwards displacement of sea surface height during the tsunami:

Map showing tsunami heights on December 26, 2004 made from NOAA radar data.

Some idea of the ability of the tsunami waves to destroy not only property but the land itself is evident in these two satellite images:

Trinkat island off the coast of India; before and after the tsunami.
Katcha island near the Indian coast; before and after the tsunami.

The southwest coastline of Sumatra suffered extraordinary levels of damage, with villages and vegetation being washed away:

Before and after the tsunami that swept over this village in Sumatra.

Hardest hit was the capital of the Aceh province of Sumatra, Banda Aceh. Here are Quickbird images of much of this city of several hundred thousand on June 23, 2004 before the tsunami struck and again after it obliterated much of the land as seen on December 28, 2004:

Pre-tsunami view of Banda Aceh, Suumatra, June 23, 2004; Quickbird Image.
Post-tsunami view of Banda Aceh, Sumatra, Dec. 28, 2004; Quickbird Image.

The tsunami generally carried for several hundred meters onto land beyond the shoreline. As the waves receded, they carried debris and soil well out into the ocean. The strong increase in the resulting sediment appears in this satellite image of the coastline near Cuddalore, in southeast India:

Tsunami-transported sediment in the Indian Ocean of southeastern India.

Earthquakes such as the December 2004 Sumatra event can cause permanent displacements of the ground - both on land and at the ocean floor. Movement along the low angle thrust that led to this earthquake extended for perhaps 800 km (500 miles) laterally. Parts of the ocean surface sank; other parts rose. In the Andoman Islands (Indian Ocean) this pair of ASTER images shows North Reef Island before and after the quake. It is obvious that the land rose here, killing off some of the now-exposed coral reef surrounding the island.

Rise of North Reef Island caused by displacement during the December 26, 2004 earthquake.

China experienced a major earthquake disaster just 3 months before the start of the International Olympics in Beijing. On May 12, 2008 a 7.9 quake whose epicenter was situated in the mountains in Sichuan Province; it was followed by several strong aftershocks:

Map of part of Sichuan Province, made from data acquired by the Shuttle Radar Topography Mission, showing the location of earthquake epicenters.

Over the region, as many as 80000 lost their lives. Here is a before and after image pair of the town of Beichuan (about 90000 people); interestingly, it was taken by Formosasat-2, and supplied to mainland China by the Taiwanese:

Beichuan before the quake Beichuan after the quake.

The right image shows that there is a landslide. Landslides are frequent sources of destruction both when they occur during or immediately after the quake and because of increased instability when set off by rains. This Sichuan scene shows the devastation caused by the May 12th earthquake:

Formosasat-2 images of a terrain affected by a landslide set off by the Sichuan earthquake.

The Sichuan landslides have created a very dangerous situation in some areas. In the steep terrain, the landslides have blocked streams, creating natural dams. Water has rapidly built up lakes that in place threaten to break through, causing potentially catastrophic floods. Chinese engineers are blowing apart certain lakes, after tens of thousands were evacuated. These Formosasat images show one such threatening new lake as it built up:

Three Formosasat images showing a lake near Beichuan formed as waters backed up behind a landslide (not shown).

Satellite data will likely play an important role in any future geologic "catastrophes". Images are especially valuable because they usually would show the extent of building damage. Ground displacement, landslides caused by earthquakes, volcanic eruptions, or heavy rains are another geologic phenomenon having ecological manifestations.