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Just before it started, the geology meeting at the Santa Barbara Central Library on Thursday looked like this from the front of the room (where I also tweeted the same pano):

Geologist Ed Keller

Our speakers were geology professor Ed Keller of UCSB and Engineering Geologist Larry Gurrola, who also works and studies with Ed. That’s Ed in the shot below.

As a geology freak, I know how easily terms like “debris flow,” “fanglomerate” and “alluvial fan” can clear a room. But this gig was SRO. That’s because around 3:15 in the morning of January 9th, debris flowed out of canyons and deposited fresh fanglomerate across the alluvial fan that comprises most of Montecito, destroying (by my count on the map below) 178 buildings, damaging more than twice that many, and killing 23 people. Two of those—a 2 year old girl and a 17 year old boy—are still interred in the fresh fanglomerate and sought by cadaver dogs. The whole thing is beyond sad and awful.

The town was evacuated after the disaster so rescue and recovery work could proceed without interference, and infrastructure could be found and repaired: a job that required removing twenty thousand truckloads of mud and rocks. That work continues while evacuation orders are gradually lifted, allowing the town to repopulate itself to the very limited degree it can.

I talked today with a friend whose business is cleaning houses. Besides grieving the dead, some of whom were friends or customers, she reports that the cleaning work is some of the worst she has ever seen, even in homes that were spared the mud and rocks. Refrigerators and freezers, sitting closed and without electricity for weeks, reek of death and rot. Other customers won’t be back because their houses are gone.

Highway 101, one of just two freeways connecting Northern and Southern California, runs through town near the coast and more than two miles from the mountain front. Three debris flows converged on the highway and used it as a catch basin, filling its deep parts to the height of at least one bridge before spilling over its far side and continuing to the edge of the sea. It took two weeks of constant excavation and repair work before traffic could move again. Most exits remain closed. Coast Village Road, Montecito’s Main Street, is open for employees of stores there, but little is open for customers yet, since infrastructural graces such as water are not fully restored. (I saw the Honor Bar operating with its own water tank, and a water truck nearby.) Opening Upper Village will take longer. Some landmark institutions, such as San Ysidro Ranch and La Casa Santa Maria, will take years to restore. (From what I gather, San Ysidro Ranch, arguably the nicest hotel in the world, was nearly destroyed. Its website thank firefighters for salvation from the Thomas Fire. But nothing, I gather, could have save it from the huge debris flow wiped out nearly everything on the flanks of San Ysidro Creek. (All the top red dots along San Ysidro Creek in the map below mark lost buildings at the Ranch.)

Here is a map with final damage assessments. I’ve augmented it with labels for the canyons and creeks (with one exception: a parallel creek west of Toro Canyon Creek):

Click on the map for a closer view, or click here to view the original. On that one you can click on every dot and read details about it.

I should pause to note that Montecito is no ordinary town. Demographically, it’s Beverly Hills draped over a prettier landscape and attractive to people who would rather not live in Beverly Hills. (In fact the number of notable persons Wikipedia lists for Montecito outnumbers those it lists for Beverly Hills by a score of 77 to 71.) Culturally, it’s a village. Last Monday in The New Yorker, one of those notable villagers, T.Coraghessan Boyle, unpacked some other differences:

I moved here twenty-five years ago, attracted by the natural beauty and semirural ambience, the short walk to the beach and the Lower Village, and the enveloping views of the Santa Ynez Mountains, which rise abruptly from the coastal plain to hold the community in a stony embrace. We have no sidewalks here, if you except the business districts of the Upper and Lower Villages—if we want sidewalks, we can take the five-minute drive into Santa Barbara or, more ambitiously, fight traffic all the way down the coast to Los Angeles. But we don’t want sidewalks. We want nature, we want dirt, trees, flowers, the chaparral that did its best to green the slopes and declivities of the mountains until last month, when the biggest wildfire in California history reduced it all to ash.

Fire is a prerequisite for debris flows, our geologists explained. So is unusually heavy rain in a steep mountain watershed. There are five named canyons, each its own watershed, above Montecito, as we see on the map above. There are more to the east, above Summerland and Carpinteria, the next two towns down the coast. Those towns also took some damage, though less than Montecito.

Ed Keller put up this slide to explain conditions that trigger debris flows, and how they work:

Ed and Larry were emphatic about this: debris flows are not landslides, nor do many start that way (though one did in Rattlesnake Canyon 1100 years ago). They are also not mudslides, so we should stop calling them that. (Though we won’t.)

Debris flows require sloped soils left bare and hydrophobic—resistant to water—after a recent wildfire has burned off the chaparral that normally (as geologists say) “hairs over” the landscape. For a good look at what soil surfaces look like, and are likely to respond to rain, look at the smooth slopes on the uphill side of 101 east of La Conchita. Notice how the surface is not only a smooth brown or gray, but has a crust on it. In a way, the soil surface has turned to glass. That’s why water runs off of it so rapidly.

Wildfires are common, and chaparral is adapted to them, becoming fuel for the next fire as it regenerates and matures. But rainfalls as intense as this one are not common. In just five minutes alone, more than half an inch of rain fell in the steep and funnel-like watersheds above Montecito. This happens about once every few hundred years, or about as often as a tsunami.

It’s hard to generalize about the combination of factors required, but Ed has worked hard to do that, and this slide of his is one way of illustrating how debris flows happen eventually in places like Montecito and Santa Barbara:

From bottom to top, here’s what it says:

  1. Fires happen almost regularly, spreading most widely where chaparral has matured to become abundant fuel, as the firefighters like to call it.
  2. Flood events are more random, given the relative rarity of rain and even more rare rains of “biblical” volume. But they do happen.
  3. Stream beds in the floors of canyons accumulate rocks and boulders that roll down the gradually eroding slopes over time. The depth of these is expressed as basin instablity. Debris flows clear out the rocks and boulders when a big flood event comes right after a fire and basin becomes stable (relatively rock-free) again.
  4. The sediment yield in a flood (F) is maximum when a debris flow (DF) occurs.
  5. Debris flows tend to happen once every few hundred years. And you’re not going to get the big ones if you don’t have the canyon stream bed full of rocks and boulders.

About this set of debris flows in particular:

  1. Destruction down Oak Creek wasn’t as bad as on Montecito, San Ysidro, Buena Vista and Romero Creeks because the canyon feeding it is smaller.
  2. When debris flows hit an obstruction, such as a bridge, they seek out a new bed to flow on. This is one of the actions that creates an alluvial fan. From the map it appears something like that happened—
    1. Where the flow widened when it hit Olive Mill Road, fanning east of Olive Mill to destroy all three blocks between Olive Mill and Santa Elena Lane before taking the Olive Mill bridge across 101 and down to the Biltmore while also helping other flows fill 101 as well. (See Mac’s comment below, and his link to a top map.)
    2. In the area between Buena Vista Creek and its East Fork, which come off different watersheds
    3. Where a debris flow forked south of Mountain Drive after destroying San Ysidro Ranch, continuing down both Randall and El Bosque Roads.

For those who caught (or are about to catch) Ellen’s Facetime with Oprah visiting neighbors, that happened among the red dots at the bottom end of the upper destruction area along San Ysidro Creek, just south of East Valley Road. Oprah’s own place is in the green area beside it on the left, looking a bit like Versailles. (Credit where due, though: Oprah’s was a good and compassionate report.)

Big question: did these debris flows clear out the canyon floors? We (meaning our geologists, sedimentologists, hydrologists and other specialists) won’t know until they trek back into the canyons to see how it all looks. Meanwhile, we do have clues. For example, here are after-and-before photos of Montecito, shot from space. And here is my close-up of the latter, shot one day after the event, when everything was still bare streambeds in the mountains and fresh muck in town:

See the white lines fanning back into the mountains through the canyons (Cold Spring, San Ysidro, Romero, Toro) above Montecito? Ed explained that these appear to be the washed out beds of creeks feeding into those canyons. Here is his slide showing Cold Spring Creek before and after the event:

Looking back at Ed’s basin threshold graphic above, one might say that there isn’t much sediment left for stream beds to yield, and that those in the floors of the canyons have returned to stability, meaning there’s little debris left to flow.

But that photo was of just one spot. There are many miles of creek beds to examine back in those canyons.

Still, one might hope that Montecito has now had its required 200-year event, and a couple more centuries will pass before we have another one.

Ed and Larry caution against such conclusions, emphasizing that most of Montecito’s and Santa Barbara’s inhabited parts gain their existence, beauty or both by grace of debris flows. If your property features boulders, Ed said, a debris flow put them there, and did that not long ago in geologic time.

For an example of boulders as landscape features, here are some we quarried out of our yard more than a decade ago, when we were building a house dug into a hillside:

This is deep in the heart of Santa Barbara.

The matrix mud we now call soil here is likely a mix of Juncal and Cozy Dell shale, Ed explained. Both are poorly lithified silt and erode easily. The boulders are a mix of Matilija and Coldwater sandstone, which comprise the hardest and most vertical parts of the Santa Ynez mountains. The two are so similar that only a trained eye can tell them apart.

All four of those geological formations were established long after dinosaurs vanished. All also accumulated originally as sediments, mostly on ocean floors, probably not far from the equator.

To illustrate one chapter in the story of how those rocks and sediments got here, UCSB has a terrific animation of how the transverse (east-west) Santa Ynez Mountains came to be where they are. Here are three frames in that movie:

What it shows is how, when the Pacific Plate was grinding its way northwest about eighteen million years ago, a hunk of that plate about a hundred miles long and the shape of a bread loaf broke off. At the top end was the future Malibu hills and at the bottom end was the future Point Conception, then situated south of what’s now Tijuana. The future Santa Barbara was west of the future Newport Beach. Then, when the Malibu end of this loaf got jammed at the future Los Angeles, the bottom end of the loaf swept out, clockwise and intact. At the start it was pointing at 5 o’clock and at the end (which isn’t), it pointed at 9:00. This was, and remains, a sideshow off the main event: the continuing crash of the Pacific Plate and the North American one.

Here is an image that helps, from that same link:

Find more geology, with lots of links, in Making sense of what happened to Montecito. I put that post up on the 15th and have been updating it since then. It’s the most popular post in the history of this blog, which I started in 2007. There are also 58 comments, so far.

I’ll be adding more to this post after I visit as much as I can of Montecito (exclusion zones permitting). Meanwhile, I hope this proves useful. Again, corrections and improvements are invited.

30 January


This post continues the inquiry I started with Making sense of what happened to Montecito. That post got a record number of reads for this blog, and 57 comments as well.

I expect to learn more at the community meeting this evening with UCSB geologist Ed Keller in the Faulkner Room in the main library in Santa Barbara. Here’s the Library schedule. Note that the meeting will be streamed live on Facebook.

Meanwhile, to help us focus on the geology questions, here is the final post-mudslide damage inspection map of Montecito:

I left out Carpinteria, because of the four structures flagged there, three were blue (affected) and one was yellow (minor), and none were orange (major) or red (destroyed). I’m also guessing they were damaged by flooding rather than debris flow. I also want to make the map as legible as possible, so we can focus on where the debris flows happened, and how we might understand the community’s prospects for the future.

So here are my questions, all subject to revision and correction.

  1. How much of the damage was due to debris flow alone, and how much to other factors (e.g. rain-caused flooding, broken water pipes)?
  2. Was concentration of rain the main reason why we saw flows in the canyons above Montecito, but not (or less so) elsewhere?
  3. Where exactly did the debris flow from? And has the area been surveyed well enough to predict what future debris flows might happen if we get big rains this winter and ones to follow?
  4. Do we need bigger catch basins for debris, like they have at the base of the San Gabriels, above Los Angeles’ basin?
  5. How do the slopes above Montecito and Santa Barbara differ from other places (e.g. the San Gabriels) where debris flows (and rock falls) are far more common?
  6. What geology-advised changes in our infrastructure (especially water and gas) might we make, based on what we’ve learned so far?
  7. What might we expect (that most of us don’t now) in the form of other catastrophes that show up in the geologic record? For example, earthquakes and tsunamis. See here: “This earthquake was associated with by far the largest seismic sea wave ever reported for one originating in California. Descriptive accounts indicate that it may have reached elevations of 15 feet at Gaviota, 30 to 35 feet at Santa Barbara, and 15 feet or more in Ventura. It may have even shown visible effects in the San Francisco harbor.” There is also this, which links to questions about the former report. (Still, there have been a number of catastrophic earthquakes on or affecting the South Coast, and it has been 93 years since the 1925 quake — and the whole Pacific Coast is subject to tsunamis. Here are some photos of the quake.)

Note that I don’t want to ask Ed to play a finger-pointing role here. Laying blame isn’t his job, unless he’s blaming nature for being itself.

Additional reading:

  • Dan McCaslin: Rattlesnake Canyon Fine Now for Day Hiking (Noozhawk) Pull-quote: “Santa Barbara geologist Ed Keller has said that all of Santa Barbara is built on debris flows piled up during the past 60,000 years. Around 1100 A.D., a truly massive debris flow slammed through Rattlesnake Canyon into Mission Canyon, leaving large boulders as far down as the intersection of Alamar Avenue and State Street (go check). There were Chumash villages in the area, and they may have been completely wiped out then. While some saddened Montecitans claim that sudden flash floods and debris flows should have been forecast more accurately, this seems impossible.”
  • Those deadly mudslides you’ve read about? Expect worse in the future. (Wall Street Journal) Pull-quote: “Montecito is particularly at risk as the hill slopes above town are oversteepened by faulting and rapid uplift, and much of the town is built on deposits laid down by previous floods. Some debris basins were in place, but they were quickly overtopped by the hundreds of thousands of cubic yards of water and sediment. While high post-fire runoff and erosion rates could be expected, it was not possible to accurately predict the exact location and extreme magnitude of this particular storm and resulting debris flows.”
  • Evacuation Areas Map.
  • Thomas Fire: Forty Days of Devastation (LA Times) Includes what happened to Montecito. Excellent step-by-step 3D animation.

Here’s the latest satellite fire detection data, restricted to just the last twelve hours of the Thomas Fire, mapped on Google Earth Pro:That’s labeled 1830 Mountain Standard Time (MST), or 5:30pm Pacific, about half an hour ago as I write this.

And here are the evacuation areas:

Our home is in the orange Voluntary Evacuation area. So we made a round trip from LA to prepare the house as best we could, gather some stuff and go. Here’s a photo album of the trip, and one of the last sights we saw on our way out of town:

This, I believe, was a fire break created on the up-slope side of Toro Canyon. Whether purely preventive or not, it was very impressive.

And here is a view of the whole burn area, which stretches more than forty miles from west to east (or from Montecito to Fillmore):

Here you can see how there is no fresh fire activity near Lake Casitas and Carpinteria, which is cool (at least relatively). You can also see how Ojai and Carpinteria were saved, how Santa Barbara is threatened, and how there are at least five separate fires around the perimeter. Three of those are in the back country, and I suspect the idea is to let those burn until they hit natural fire breaks or the wind shifts and the fires get blown back on their own burned areas and fizzle out there.

The main area of concern is at the west end of the fire, above Santa Barbara, in what they call the front country: the slope on the ocean’s side of the Santa Ynez Mountains, which run as a long and steep spine, rising close to 4000 feet high in the area we care about here. (It’s higher farther west.)

This afternoon I caught a community meeting on KEYT, Santa Barbara’s TV station, which has been very aggressive and responsible in reporting on the fire. I can’t find a recording of that meeting now on the station’s website, but I am watching the station’s live 6pm news broadcast now, devoted to a news conference at the Ventura County Fairgrounds. (Even though I’m currently at a house near Los Angeles, I can watch our TV set top box remotely through a system called Dish Anywhere. Hats off to Dish Network for providing that ability. In addition to being cool, it’s exceptionally handy for evacuated residents whose homes still have electricity and a good Internet connection. I thank Southern California Edison and Cox for those.)

On KEYT, Mark Brown of @Cal_Fire just spoke about Plans A, B and C, one or more of which will be chosen based on how the weather moves. Plan C is the scariest (and he called it that), because it involves setting fire lines close to homes, intentionally scorching several thousand acres to create an already-burned break, to stop the fire. “The vegetation will be removed before the fire has a chance to take it out, the way it wants to take it out,” he says.

Okay, that briefing just ended. I’ll leave it there.

So everybody reading this knows, we are fine, and don’t need to be at the house while this is going on. We also have great faith that 8000 fire fighting personnel and all their support systems will do the job and save our South Coast communities. What they’ve done so far has been nothing short of amazing, given the enormous geographical extent of this fire, the exceptionally rugged nature of the terrain, the record dryness of the vegetation, and other disadvantages. A huge hat tip to them.