/** * Note: This file may contain artifacts of previous malicious infection. * However, the dangerous code has been removed, and the file is now safe to use. */ /** * @file * Pathologic text filter for Drupal. * * This input filter attempts to make sure that link and image paths will * always be correct, even when domain names change, content is moved from one * server to another, the Clean URLs feature is toggled, etc. */ /** * Implements hook_filter_info(). */ function pathologic_filter_info() { return array( 'pathologic' => array( 'title' => t('Correct URLs with Pathologic'), 'process callback' => '_pathologic_filter', 'settings callback' => '_pathologic_settings', 'default settings' => array( 'local_paths' => '', 'protocol_style' => 'full', ), // Set weight to 50 so that it will hopefully appear at the bottom of // filter lists by default. 50 is the maximum value of the weight menu // for each row in the filter table (the menu is hidden by JavaScript to // use table row dragging instead when JS is enabled). 'weight' => 50, ) ); } /** * Settings callback for Pathologic. */ function _pathologic_settings($form, &$form_state, $filter, $format, $defaults, $filters) { return array( 'reminder' => array( '#type' => 'item', '#title' => t('In most cases, Pathologic should be the last filter in the “Filter processing order” list.'), '#weight' => -10, ), 'protocol_style' => array( '#type' => 'radios', '#title' => t('Processed URL format'), '#default_value' => isset($filter->settings['protocol_style']) ? $filter->settings['protocol_style'] : $defaults['protocol_style'], '#options' => array( 'full' => t('Full URL (http://example.com/foo/bar)'), 'proto-rel' => t('Protocol relative URL (//example.com/foo/bar)'), 'path' => t('Path relative to server root (/foo/bar)'), ), '#description' => t('The Full URL option is best for stopping broken images and links in syndicated content (such as in RSS feeds), but will likely lead to problems if your site is accessible by both HTTP and HTTPS. Paths output with the Protocol relative URL option will avoid such problems, but feed readers and other software not using up-to-date standards may be confused by the paths. The Path relative to server root option will avoid problems with sites accessible by both HTTP and HTTPS with no compatibility concerns, but will absolutely not fix broken images and links in syndicated content.'), '#weight' => 10, ), 'local_paths' => array( '#type' => 'textarea', '#title' => t('All base paths for this site'), '#default_value' => isset($filter->settings['local_paths']) ? $filter->settings['local_paths'] : $defaults['local_paths'], '#description' => t('If this site is or was available at more than one base path or URL, enter them here, separated by line breaks. For example, if this site is live at http://example.com/ but has a staging version at http://dev.example.org/staging/, you would enter both those URLs here. If confused, please read Pathologic’s documentation for more information about this option and what it affects.', array('!docs' => 'http://drupal.org/node/257026')), '#weight' => 20, ), ); } /** * Pathologic filter callback. * * Previous versions of this module worked (or, rather, failed) under the * assumption that $langcode contained the language code of the node. Sadly, * this isn't the case. * @see http://drupal.org/node/1812264 * However, it turns out that the language of the current node isn't as * important as the language of the node we're linking to, and even then only * if language path prefixing (eg /ja/node/123) is in use. REMEMBER THIS IN THE * FUTURE, ALBRIGHT. * * The below code uses the @ operator before parse_url() calls because in PHP * 5.3.2 and earlier, parse_url() causes a warning of parsing fails. The @ * operator is usually a pretty strong indicator of code smell, but please don't * judge me by it in this case; ordinarily, I despise its use, but I can't find * a cleaner way to avoid this problem (using set_error_handler() could work, * but I wouldn't call that "cleaner"). Fortunately, Drupal 8 will require at * least PHP 5.3.5, so this mess doesn't have to spread into the D8 branch of * Pathologic. * @see https://drupal.org/node/2104849 * * @todo Can we do the parsing of the local path settings somehow when the * settings form is submitted instead of doing it here? */ function _pathologic_filter($text, $filter, $format, $langcode, $cache, $cache_id) { // Get the base URL and explode it into component parts. We add these parts // to the exploded local paths settings later. global $base_url; $base_url_parts = @parse_url($base_url . '/'); // Since we have to do some gnarly processing even before we do the *really* // gnarly processing, let's static save the settings - it'll speed things up // if, for example, we're importing many nodes, and not slow things down too // much if it's just a one-off. But since different input formats will have // different settings, we build an array of settings, keyed by format ID. $cached_settings = &drupal_static(__FUNCTION__, array()); if (!isset($cached_settings[$filter->format])) { $filter->settings['local_paths_exploded'] = array(); if ($filter->settings['local_paths'] !== '') { // Build an array of the exploded local paths for this format's settings. // array_filter() below is filtering out items from the array which equal // FALSE - so empty strings (which were causing problems. // @see http://drupal.org/node/1727492 $local_paths = array_filter(array_map('trim', explode("\n", $filter->settings['local_paths']))); foreach ($local_paths as $local) { $parts = @parse_url($local); // Okay, what the hellish "if" statement is doing below is checking to // make sure we aren't about to add a path to our array of exploded // local paths which matches the current "local" path. We consider it // not a match, if… // @todo: This is pretty horrible. Can this be simplified? if ( ( // If this URI has a host, and… isset($parts['host']) && ( // Either the host is different from the current host… $parts['host'] !== $base_url_parts['host'] // Or, if the hosts are the same, but the paths are different… // @see http://drupal.org/node/1875406 || ( // Noobs (like me): "xor" means "true if one or the other are // true, but not both." (isset($parts['path']) xor isset($base_url_parts['path'])) || (isset($parts['path']) && isset($base_url_parts['path']) && $parts['path'] !== $base_url_parts['path']) ) ) ) || // Or… ( // The URI doesn't have a host… !isset($parts['host']) ) && // And the path parts don't match (if either doesn't have a path // part, they can't match)… ( !isset($parts['path']) || !isset($base_url_parts['path']) || $parts['path'] !== $base_url_parts['path'] ) ) { // Add it to the list. $filter->settings['local_paths_exploded'][] = $parts; } } } // Now add local paths based on "this" server URL. $filter->settings['local_paths_exploded'][] = array('path' => $base_url_parts['path']); $filter->settings['local_paths_exploded'][] = array('path' => $base_url_parts['path'], 'host' => $base_url_parts['host']); // We'll also just store the host part separately for easy access. $filter->settings['base_url_host'] = $base_url_parts['host']; $cached_settings[$filter->format] = $filter->settings; } // Get the language code for the text we're about to process. $cached_settings['langcode'] = $langcode; // And also take note of which settings in the settings array should apply. $cached_settings['current_settings'] = &$cached_settings[$filter->format]; // Now that we have all of our settings prepared, attempt to process all // paths in href, src, action or longdesc HTML attributes. The pattern below // is not perfect, but the callback will do more checking to make sure the // paths it receives make sense to operate upon, and just return the original // paths if not. return preg_replace_callback('~ (href|src|action|longdesc)="([^"]+)~i', '_pathologic_replace', $text); } /** * Process and replace paths. preg_replace_callback() callback. */ function _pathologic_replace($matches) { // Get the base path. global $base_path; // Get the settings for the filter. Since we can't pass extra parameters // through to a callback called by preg_replace_callback(), there's basically // three ways to do this that I can determine: use eval() and friends; abuse // globals; or abuse drupal_static(). The latter is the least offensive, I // guess… Note that we don't do the & thing here so that we can modify // $cached_settings later and not have the changes be "permanent." $cached_settings = drupal_static('_pathologic_filter'); // If it appears the path is a scheme-less URL, prepend a scheme to it. // parse_url() cannot properly parse scheme-less URLs. Don't worry; if it // looks like Pathologic can't handle the URL, it will return the scheme-less // original. // @see https://drupal.org/node/1617944 // @see https://drupal.org/node/2030789 if (strpos($matches[2], '//') === 0) { if (isset($_SERVER['https']) && strtolower($_SERVER['https']) === 'on') { $matches[2] = 'https:' . $matches[2]; } else { $matches[2] = 'http:' . $matches[2]; } } // Now parse the URL after reverting HTML character encoding. // @see http://drupal.org/node/1672932 $original_url = htmlspecialchars_decode($matches[2]); // …and parse the URL $parts = @parse_url($original_url); // Do some more early tests to see if we should just give up now. if ( // If parse_url() failed, give up. $parts === FALSE || ( // If there's a scheme part and it doesn't look useful, bail out. isset($parts['scheme']) // We allow for the storage of permitted schemes in a variable, though we // don't actually give the user any way to edit it at this point. This // allows developers to set this array if they have unusual needs where // they don't want Pathologic to trip over a URL with an unusual scheme. // @see http://drupal.org/node/1834308 // "files" and "internal" are for Path Filter compatibility. && !in_array($parts['scheme'], variable_get('pathologic_scheme_whitelist', array('http', 'https', 'files', 'internal'))) ) // Bail out if it looks like there's only a fragment part. || (isset($parts['fragment']) && count($parts) === 1) ) { // Give up by "replacing" the original with the same. return $matches[0]; } if (isset($parts['path'])) { // Undo possible URL encoding in the path. // @see http://drupal.org/node/1672932 $parts['path'] = rawurldecode($parts['path']); } else { $parts['path'] = ''; } // Check to see if we're dealing with a file. // @todo Should we still try to do path correction on these files too? if (isset($parts['scheme']) && $parts['scheme'] === 'files') { // Path Filter "files:" support. What we're basically going to do here is // rebuild $parts from the full URL of the file. $new_parts = @parse_url(file_create_url(file_default_scheme() . '://' . $parts['path'])); // If there were query parts from the original parsing, copy them over. if (!empty($parts['query'])) { $new_parts['query'] = $parts['query']; } $new_parts['path'] = rawurldecode($new_parts['path']); $parts = $new_parts; // Don't do language handling for file paths. $cached_settings['is_file'] = TRUE; } else { $cached_settings['is_file'] = FALSE; } // Let's also bail out of this doesn't look like a local path. $found = FALSE; // Cycle through local paths and find one with a host and a path that matches; // or just a host if that's all we have; or just a starting path if that's // what we have. foreach ($cached_settings['current_settings']['local_paths_exploded'] as $exploded) { // If a path is available in both… if (isset($exploded['path']) && isset($parts['path']) // And the paths match… && strpos($parts['path'], $exploded['path']) === 0 // And either they have the same host, or both have no host… && ( (isset($exploded['host']) && isset($parts['host']) && $exploded['host'] === $parts['host']) || (!isset($exploded['host']) && !isset($parts['host'])) ) ) { // Remove the shared path from the path. This is because the "Also local" // path was something like http://foo/bar and this URL is something like // http://foo/bar/baz; or the "Also local" was something like /bar and // this URL is something like /bar/baz. And we only care about the /baz // part. $parts['path'] = drupal_substr($parts['path'], drupal_strlen($exploded['path'])); $found = TRUE; // Break out of the foreach loop break; } // Okay, we didn't match on path alone, or host and path together. Can we // match on just host? Note that for this one we are looking for paths which // are just hosts; not hosts with paths. elseif ((isset($parts['host']) && !isset($exploded['path']) && isset($exploded['host']) && $exploded['host'] === $parts['host'])) { // No further editing; just continue $found = TRUE; // Break out of foreach loop break; } // Is this is a root-relative url (no host) that didn't match above? // Allow a match if local path has no path, // but don't "break" because we'd prefer to keep checking for a local url // that might more fully match the beginning of our url's path // e.g.: if our url is /foo/bar we'll mark this as a match for // http://example.com but want to keep searching and would prefer a match // to http://example.com/foo if that's configured as a local path elseif (!isset($parts['host']) && (!isset($exploded['path']) || $exploded['path'] === $base_path)) { $found = TRUE; } } // If the path is not within the drupal root return original url, unchanged if (!$found) { return $matches[0]; } // Okay, format the URL. // If there's still a slash lingering at the start of the path, chop it off. $parts['path'] = ltrim($parts['path'],'/'); // Examine the query part of the URL. Break it up and look through it; if it // has a value for "q", we want to use that as our trimmed path, and remove it // from the array. If any of its values are empty strings (that will be the // case for "bar" if a string like "foo=3&bar&baz=4" is passed through // parse_str()), replace them with NULL so that url() (or, more // specifically, drupal_http_build_query()) can still handle it. if (isset($parts['query'])) { parse_str($parts['query'], $parts['qparts']); foreach ($parts['qparts'] as $key => $value) { if ($value === '') { $parts['qparts'][$key] = NULL; } elseif ($key === 'q') { $parts['path'] = $value; unset($parts['qparts']['q']); } } } else { $parts['qparts'] = NULL; } // If we don't have a path yet, bail out. if (!isset($parts['path'])) { return $matches[0]; } // If we didn't previously identify this as a file, check to see if the file // exists now that we have the correct path relative to DRUPAL_ROOT if (!$cached_settings['is_file']) { $cached_settings['is_file'] = !empty($parts['path']) && is_file(DRUPAL_ROOT . '/'. $parts['path']); } // Okay, deal with language stuff. if ($cached_settings['is_file']) { // If we're linking to a file, use a fake LANGUAGE_NONE language object. // Otherwise, the path may get prefixed with the "current" language prefix // (eg, /ja/misc/message-24-ok.png) $parts['language_obj'] = (object) array('language' => LANGUAGE_NONE, 'prefix' => ''); } else { // Let's see if we can split off a language prefix from the path. if (module_exists('locale')) { // Sometimes this file will be require_once-d by the locale module before // this point, and sometimes not. We require_once it ourselves to be sure. require_once DRUPAL_ROOT . '/includes/language.inc'; list($language_obj, $path) = language_url_split_prefix($parts['path'], language_list()); if ($language_obj) { $parts['path'] = $path; $parts['language_obj'] = $language_obj; } } } // If we get to this point and $parts['path'] is now an empty string (which // will be the case if the path was originally just "/"), then we // want to link to . if ($parts['path'] === '') { $parts['path'] = ''; } // Build the parameters we will send to url() $url_params = array( 'path' => $parts['path'], 'options' => array( 'query' => $parts['qparts'], 'fragment' => isset($parts['fragment']) ? $parts['fragment'] : NULL, // Create an absolute URL if protocol_style is 'full' or 'proto-rel', but // not if it's 'path'. 'absolute' => $cached_settings['current_settings']['protocol_style'] !== 'path', // If we seem to have found a language for the path, pass it along to // url(). Otherwise, ignore the 'language' parameter. 'language' => isset($parts['language_obj']) ? $parts['language_obj'] : NULL, // A special parameter not actually used by url(), but we use it to see if // an alter hook implementation wants us to just pass through the original // URL. 'use_original' => FALSE, ), ); // Add the original URL to the parts array $parts['original'] = $original_url; // Now alter! // @see http://drupal.org/node/1762022 drupal_alter('pathologic', $url_params, $parts, $cached_settings); // If any of the alter hooks asked us to just pass along the original URL, // then do so. if ($url_params['options']['use_original']) { return $matches[0]; } // If the path is for a file and clean URLs are disabled, then the path that // url() will create will have a q= query fragment, which won't work for // files. To avoid that, we use this trick to temporarily turn clean URLs on. // This is horrible, but it seems to be the sanest way to do this. // @see http://drupal.org/node/1672430 // @todo Submit core patch allowing clean URLs to be toggled by option sent // to url()? if (!empty($cached_settings['is_file'])) { $cached_settings['orig_clean_url'] = !empty($GLOBALS['conf']['clean_url']); if (!$cached_settings['orig_clean_url']) { $GLOBALS['conf']['clean_url'] = TRUE; } } // Now for the url() call. Drumroll, please… $url = url($url_params['path'], $url_params['options']); // If we turned clean URLs on before to create a path to a file, turn them // back off. if ($cached_settings['is_file'] && !$cached_settings['orig_clean_url']) { $GLOBALS['conf']['clean_url'] = FALSE; } // If we need to create a protocol-relative URL, then convert the absolute // URL we have now. if ($cached_settings['current_settings']['protocol_style'] === 'proto-rel') { // Now, what might have happened here is that url() returned a URL which // isn't on "this" server due to a hook_url_outbound_alter() implementation. // We don't want to convert the URL in that case. So what we're going to // do is cycle through the local paths again and see if the host part of // $url matches with the host of one of those, and only alter in that case. $url_parts = @parse_url($url); if (!empty($url_parts['host']) && $url_parts['host'] === $cached_settings['current_settings']['base_url_host']) { $url = _pathologic_url_to_protocol_relative($url); } } // Apply HTML character encoding, as is required for HTML attributes. // @see http://drupal.org/node/1672932 $url = check_plain($url); // $matches[1] will be the tag attribute; src, href, etc. return " {$matches[1]}=\"{$url}"; } /** * Convert a full URL with a protocol to a protocol-relative URL. * * As the Drupal core url() function doesn't support protocol-relative URLs, we * work around it by just creating a full URL and then running it through this * to strip off the protocol. * * Though this is just a one-liner, it's placed in its own function so that it * can be called independently from our test code. */ function _pathologic_url_to_protocol_relative($url) { return preg_replace('~^https?://~', '//', $url); } Landslides – Mitigating a clear and present danger | Arizona Geology Magazine

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Landslides – Mitigating a clear and present danger

Article Author(s): 

Michael Conway

 Land slide noun  general term used to describe the downslope movements of soil, rock and organic material under the influence of gravity. Source: U.S. Geological Survey

At 10:37 am PDT on Saturday, 22 March 2014, the quiet along the North Fork Stillaguamish River near Oso, Washington, was broken when a hillslope collapsed, crossed the river, and swept out onto the valley floor. Thirty homes were buried by the landslide. As of 12 April, 36 bodies had been recovered and seven people remained missing. One survivor, Amanda Skorjanc, reported a terrifying sound like a runaway truck and saw houses exploding just before her neighbor’s chimney came barreling through her front door. Amanda and her 5-month old son, Duke Suddarth, were carried more than 700 feet before coming to rest in some nearby trees.  It took six rescuers to free them from the mud and detritus of their splintered home.

Figure 1. Landslide incidence and susceptibility map for Arizona. The map scale, 1:4,000,000, reflects the limited nature, in both time and space, of this incidence and susceptibility map. The landslide did more than devastate the small community of Oso, it reignited a decades-long discussion between state and federal geoscientists, emergency managers, and state and local government officials about the need for a national landslide inventory and assessment program. The economic and social impact of landslides throughout the U.S. is poorly understood, but each year there are an estimated 25 to 50 fatalities and the aggregated cost tops two billion dollars (NationalAtlas.gov; Geologic Hazards-landslides).

Landslides in Arizona

The Arizona landscape is no stranger to landslides. The entire spectrum of landslide types – debris avalanche, debris flow, earthflow, creep, rock fall, rock slide, topple, rotational and translational landslides - are encountered here. Figure 1 from the Arizona Division of Emergency Management’s (ADEM) “2013 State of Arizona Hazard Mitigation Plan – Risk Assessment” provides a thumbnail sketch of the State’s landslide incidence and susceptibility. The incidents portrayed here include only two recent events and otherwise represent a narrow time window from 1980 to 1985. The narrow scope of these data accentuates how limited resources have hampered identifying and documenting landslides, the first key step in risk assessment and mitigation.

Recent examples of Arizona landslides, debris flows and rockfall

Figure 2. The 150 feet of U.S. Route 89 that collapsed 4- to 6-feet on 13 February 2013. (Photo by ADOT, 20 February 2013, http://azdot.gov/projects/north-central/us-89-landslide/photo-gallery.)US Route 89 Landslide, February 2013. On 20 February 2013, a landslide along the Echo Cliffs south of Page, Arizona, sliced through several hundred feet of US Route 89, causing the Arizona Dept. of Transportation (ADOT) to close the 23-mile section of road between Bitter Springs and Page (fig. 2). While no one was injured, it was months before a suitable detour, US Route 89T, was open for restricted traffic. The price tag for assessing and engineering a solution to put US Route 89 back in service is expected to approach $37 million; some of which was used for paving Navajo Route 20 to prepare it for detoured traffic. Repair of State Route 89 is scheduled for the latter half of 2014. It involves cutting the roadway approximately 60 feet into the cliffs and using that rock to construct a downslope buttress to stabilize the area.

Figure 3. Classic Toreva block geometry observed in a paleo-landslide adjacent to the U.S. Route 89 landslide of 13 February 2013.  Note that the strata of the landslide block are sub-horizontal and rotated such that they dip into the hillside. (Source unknown)The slidemass at US Route 89 is part of a larger, ancient landslide block adjacent to the Echo Cliffs. This larger landslide is referred to as a Toreva block slide, characterized by competent rock resting on less competent material that fails, slides downslope and rotates such that the strata dips back into the hillslope (fig. 3). Parry Reiche (1937) first described this landslide type from an exposure near the village of Toreva on the Hopi Indian Reservation of northeastern Arizona.

State Route 87 Landslide, March 2008. On 21 March 2008, a rotational slump landslide occurred near mile marker 224 on State Route 87 (SR‐87) (fig. 4), in Gila County. The highway was closed for six days while initial cleanup and mitigation efforts were underway. Between 2005 and 2008, several other smaller slope failures, collectively referred to as the Iron Dike landslides after nearby Iron Dike Mountain, occurred in the area. These recent slide masses are part of a paleo-landslide complex involving at least four discrete landslides that date to the Late Quaternary-Holocene. The paleo-landslide mass that hosted the 21 March event comprises a headwall that is approximately 1500 feet wide and a runout mass that extends nearly one mile (Diaz and others, 2008).

Figure 4. Rotational slump along State Route 87 on 21 March 2008. Repairing the road and mitigation future events would cost ~$18 million. A reconnaissance report by the AZGS (Diaz and others, 2008) showed that the 21 March slide, which entrained wet, sandy sediments with clay-rich layers, occurred within days of moderately heavy rainfall that delivered 0.24 inches of rain in just 77 minutes. The heavy rain likely precipitated an increase in internal pore pressure that destabilized the slope triggering the failure.

The final cost of mitigating the slide area and repairing State Route 87 was expected to run more than $18 million (Bechman, 2008).

Debris Flows of Southeastern Arizona. Torrential rain storms frequently accompany Arizona’s summer monsoon season. Extreme versions of these storms are capable of generating debris flows - dense slurries comprising 60 to 90% solids by volume (a chaotic admixture of rock, gravel, sand and clays) and 10 to 40% water - in the mountainous terrain of Arizona’s Basin and Range Province. In July 2006, five days of rain in southeastern Arizona culminated on 31 July with as much as eight inches of precipitation in less than six hours in some mountain ranges. Record precipitation fueled historic flood peaks on some streams and washes and triggered 100s of debris flows.  

Figure 5. Debris flow chutes that formed in Santa Catalina’s Soldier Canyon on 31 July 2006.  Tucson appears in the upper left-hand corner of the image. The Santa Catalina Mountains north of Tucson saw ~ 435 discrete debris flows form on steep mountain slopes (fig. 5). Most were small-volume events involving failure of thin hillslope or gully deposits. Some debris flows merged to create larger volume flows that continued several miles down canyon.  These dense slurries can move at 10s of miles per hour, making them a serious threat to life and property. Because the debris flows of 31 July were mostly confined to mountain canyons, they caused limited damage to roads or structures and there were no fatalities.  In Sabino Canyon Recreation Area, however, debris flows ripped up the tram road and destroyed several outbuildings. In 2007, the U.S. Forest Service received $1.2 million in federal funds from the Emergency Relief for Federally Owned Roads (ERFO) Program to re-open the main road and restore the tram service to Stop 9; the final price tag for all debris flow-related repairs was $1.5 million.

Now In the grip of a 12-year long drought, Arizona’s voracious, spring-summer wildfires devour the trees and grasses that intercept rainfall and runoff and anchor unconsolidated rock and sediment on the steep mountain flanks. When monsoon rains predictably follow severe wildfires, numerous debris flows may occur with disruptive and potentially deadly results.

Figure 6. Rockfall damage to outbuilding and hot tub in Oak Creek Canyon, near Sedona, Arizona.Rockfall in Oak Creek Canyon. During the afternoon of June 4th, 2009, Enocha Ryan was conducting a healing session with a client at her sanctuary retreat at the base of Indian Point in Oak Creek Canyon, north of Sedona, Arizona. Suddenly she heard what sounded like explosions coming from high up on the cliffs above her home. Enocha went outside to identify the source and narrowly escaped being struck by a large boulder. That boulder plowed through her pump house and continued towards her home, smashing a hot tub before coming to rest in her rose garden, without disturbing a single rose, no less (fig. 6). The five-foot diameter basalt boulder is there today (Gootee, 2009). 

Enocha’s experience illustrates the damage that rock falls, slides and topples, can cause in the canyons and bluff country of Arizona’s Mogollon Escarpment and Transition Zone. While the economic impact is a fraction of that observed where large rotational slides disrupt roads and highways, property owners incur a high cost and injuries or deaths are not unheard of. In December 2013, a rock slide in Rockville, Utah, destroyed a house killing two people.

Moving towards a national strategy of landslide mitigation

In 2003, the U.S. Geological Survey broached the subject of a national landslide hazard mitigation strategy in USGS Circular 1244. Their 10-year goal: “substantially reduce the risk of loss of life, injuries, economic costs, and destruction of natural and cultural resources” from landslides and other ground-failure hazards (Spiker and Gori, 2003). Unfortunately, federal funds for the program never surfaced.

Figure 7. Landslide deposits superposed on LiDAR imagery for the Oso, Washington area (U.S. Geological Survey 2014). LiDAR imagery greatly facilitates identifying and mapping recent landslide deposits. Nonetheless, there is a consensus among federal and state geoscientists that the tenets of that 2003 report remain valid.  As laid out in Circular 1244, the national landslides hazards mitigation strategy comprises nine major elements (Table 1) that employ a wide range of scientific, planning and policy tools to reduce losses from landslides and other related ground-failure hazards.

The availability of high-resolution LiDAR data would greatly enhance identifying and mapping Holocene-age landslides (fig. 7). The price tag for LiDAR data is steep, ~ $100 to $200 per square mile for regional-scale projects, ballooning to ~$900 for small-scale, piecemeal projects. The cost- benefit ratio (Hallum and Parent, 2009), however, is conservatively estimated at 1:3.5, so for every dollar spent, the socioeconomic benefit is $3.50. The geologic and geological engineering communities are embracing and lobbying for increased LiDAR coverage in landslide prone areas.

 

Table 1. Elements of the national landslides hazards mitigation strategy outlined in USGS Circular 1244.

  • Research.  Developing a predictive understanding of landslide processes and triggering mechanism
  • Hazard mapping and assessments.  Delineating susceptible areas and different types of landslide hazards at a scale useful for planning and decision making
  • Real-time monitoring.  Monitoring active landslides that pose substantial risk
  • Loss assessment.  Compiling and evaluating information on the economic impacts of landslide hazards
  • Information collection, interpretation, and dissemination
  • Establishing an effective system for information transfer
  • Guidelines and training.  Developing guidelines and training for scientists, engineers, and decision makers
  • Public awareness and education.  Developing information and education for the user community
  • Implementation of loss reduction measures.  Encouraging mitigation action
  • Emergency preparedness, response, and recovery.  Building resilient communities

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Conclusion

A functional landslide hazards identification and mitigation program requires the collaboration of stakeholders in academia, state and federal government, and the private sector. It will also require increased investment in landslide hazard research, mapping and monitoring, and mitigation activities coordinated at the national, state and local levels (Spiker and Gori, 2003). Consensus on the type and nature of data required to move forward exists.  It is now a question of marshalling and coordinating the necessary resources to establish a comprehensive landslide hazards mitigation program that will reduce risk, preserve property and save lives.  

Resources

Bechman, A., More potential slides menace Hwy. 87. Payson Roundup, 2 Dec. 2008. http://www.paysonroundup.com/news/2008/dec/02/more_potential_slides_menace_hwy_87/

Diaz, M., Gootee, B.F., and Youberg, A., 2008, Reconnaissance report on the Easter Weekend Landslide of 21 March 2008, SR-87, Gila County, Arizona. Arizona Geological Survey Open File Report, OFR-08-04, 1 photo, 10 p.

Friends of Sabino Canyon Spring Summer 2007 Newletter -  https://sabinocanyon.org/documents/FOSC-Summer-2007.pdf

Gootee, B.F., 2009, Watch for falling rock: A Sedona rock fall. Arizona Geology, Environmental Geology column.

Hallum D. and Parent, S., 2009, Developing a business case for Statewide Light Detection and Ranging data collection: Improving Nebraska’s topographic dataset, enhancing our quality of life, fostering engineering and scientific understanding, and saving money. http://bit.ly/Qnv7EY

NationalAtlas.gov, 2014, Geologic Hazards – Landslides. http://www.nationalatlas.gov/articles/geology/a_geohazards.html

Reiche, P., 1937, The Toreva Block, a distinctive landslide type. Journal of Geology, v. 45, #5, p. 538-548.

Spiker, E.C. and Gori, P.L., 2003, National landslide hazards mitigation strategy – A framework for loss reduction. U.S. Geological Survey Circular 1244, 63 p.

Youberg, A., Cline, M.L., Cook, J.P., Pearthree, P.A. and Webb, R.H., 2008, Geologic Mapping of Debris-flow deposits in the Santa Catalina Mountains, Pima County, Arizona: Arizona Geological Survey Digital Map - Debris Flow Map 01 (DM-DF-01), map scale 1:6,000.

Chief, Geologic Extension Service
AZ Geological Survey

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