So I’m Kate Allstadt from the USGS in Golden, Colorado.
And today I’m going to talk about the landslides that were triggered by the
2021 Nippes earthquake in Haiti and the rapid remote response effort
that myself and my co-authors, who are listed on the slide here,
undertook in order to provide situational awareness support.
So, though this is a northern California earthquake hazards workshop,
and Haiti is a different place, I’m hoping that you’ll see some points of relevance
with regards to, first, what tools we now have available for situational
awareness after major landslide- triggering events that we didn’t have
a few years ago, and second, what changes to the landslide hazard
outlook to expect both right after and for years after a major landslide-triggering
event, which have been known to happen in California.
And much of the work that I’m going to present on today was recently published
in a Open-File report along with a data release of the landslide inventory.
So thanks to Sabrina Martinez for seeing that through so quickly.
And so, if you want more details about what I’m going to talk about today,
I suggest that you take a look at these publications.
So, before we jump into what happened in Haiti, here’s a quick overview
of cascading hazards related to earthquake-triggered landslides.
And, so in this diagram by Fan et al., it shows the immediate effects
of the earthquake in the center. So those are the landslides triggered
by the earthquake as well as damage to the slopes caused by the shaking.
But, in the blue section, you see shorter- term hazards, such as debris flows
mobilized from the landslide deposits and also landslide dams that can form
and impound water, and they can fail catastrophically and cause flooding.
Then, in the yellow section, you see longer-term hazards, such as changing
in the – changes in the way that the rivers behave and their
flooding behavior and so on. And we also see – typically,
for several years after a earthquake, you see an increase in the overall
landslide activity because of the damaged slopes from the earthquake.
So here I’m showing a screenshot of the interactive map from the USGS
event page, and I’m showing the USGS finite faults as well as
the contours of the ShakeMap. And you can see that the earthquake
affected mainly the western half of the Tiburon Peninsula,
and it ruptured from east to west.
And so the rest of the maps, we’re going to be zooming in
on the western part of the peninsula.
And, in this map here, kind of summarizes the event and its landslides.
So you can see the epicenter in the east, and so the rupture started with more
reverse motion in the east, and then, as it progressed westward,
it’s thought to have transitioned to strike-slip motion primarily.
And it ended in the mountainous area where
there’s intense landsliding shown on this map here.
And so you can see that, in the east, the landslides are more sparsely distributed.
They kind of narrow towards the center, and then most of the intense landsliding
actually happened on the western side of the rupture.
And so some of that is thought to be probably due to directivity effects
because of the east-to-west rupture, but this area to the west is also highly
susceptible – very steep slopes, and so multiple factors were likely at play.
But I’m sure that we’ll find out more about the details of the
earthquake as research comes out in the coming months.
So, at left here, we kind of have a timeline of the sequence of
events and our response to it. So the earthquake happened
on the 14th. And, as for all major earthquakes, the USGS produced
its rapid near-real-time products, and that now includes a ground failure
product, so that’s the model shown in the background here.
And I’ll talk about that more in a minute.
Two days after the earthquake, a tropical cyclone hit the island,
dropping about 5 to 10 inches of rain. And it likely triggered more landslides,
but we don’t have the imagery resolution to separate which were from
the cyclone and which were from the earthquake from the map at right.
However, based on the characteristics of the landslides,
most of them were caused by the earthquake.
So, starting right after the earthquake, and through the end of August,
the team of seven of us worked on this rapid response and mapping effort
where we mapped collaboratively and we provided situational reports
to the USAID’s Disaster Assistance Response teams that were on the
ground here pretty much every day. And, once that rapid effort had kind of
wound down, then we worked on refining the inventory and looking
more carefully at kind of ongoing hazards of concern.
And we prepared a preliminary assessment report internally for BHA.
And then finally, we cleaned that up, and cleaned up the inventory
and prepared it all for public release, and that’s what’s available on
that Open-File report I mentioned earlier.
So going back to the USGS ground failure product, here I’m just
showing you where it lives. This is the USGS event page
for the Haiti earthquake, and you can see that the ground failure product
has its own card that summarizes the product on the event page.
And you can see that there’s information on both landslides
and liquefaction. If you click on the card, you can – you go to
a more detailed page where you can view maps and other statistics.
And I’m not going to talk about liquefaction very much,
but it is available. And the landslide model is shown at the top here,
and you can see that the summary information assigned this event
an orange alert for landslides based on both its hazard and
population exposure, which indicates a pretty significant event. There is fewer
than three orange alerts that happen per year for the ground failure product.
Another product that is not public yet that is still in testing mode, but that
we did run for this event, and we shared with responders, is this product
that takes the landslides probability model and the road network and
kind of estimates where roads might be blocked.
And so this is the result of that, and you can see some yellow areas
that were thought to have been at higher risk of being obstructed.
And this area here was a major issue because this is the main connector
between Les Cayes and Jeremie and these other areas to the north.
And so this is what that area looks like.
This is in some imagery from Google Earth.
Basically, this whole stretch of road was affected by intense landsliding.
There’s some – there was one drone video posted on Twitter showing them
trying to clear this road, but it took quite a while,
and it was a big issue for getting – for moving supplies over land.
So, as I said earlier, this was the first time that we did a entirely remote
response, and we were able to take advantage of some new tools through
ArcGIS Pro and ArcGIS Online, where the seven of us who were
involved in this effort were able to map collaboratively, you know,
in the same files, and we were able to share those updates
in real time with the public. And we mainly did this so that
responders could see this map as we were updating it,
but it was available to anybody to see as preliminary information.
And so this is showing a screenshot of what we were able to share publicly.
And we mapped about 3,600 landslides within
about two weeks of the earthquake happening.
And, as I mentioned earlier, we provided daily updates to USAID
on what we were seeing and how many landslides and so on.
So one area of early concern was the Pic Macaya National Park.
So this is imagery of the Pic Macaya National Park from right –
a few days before the earthquake. And this is imagery – this is all
Sentinel 2 imagery – from right after the earthquake.
And you can see that it was just completely devastated by landslides
in this gorge. And this was a big concern because this gorge is upstream
from many of the most populated areas in the region, so Camp Perrin and
Les Cayes are downstream from this. And there was concern that some of
these landslides might have formed landslide dams that we couldn’t see
in this low-resolution imagery, and they could fail catastrophically
and cause rapid flooding downstream.
And there was a citizen report about something like this happening.
But we did not get cloud-free imagery for quite a while after the earthquake.
Though, fortunately, USAID was able to arrange an overflight, and some
Haitian colleagues were able to get on that flight, and they flew
up the gorge and did not see anything of major concern.
And we later learned from some imagery that came in that there
had been a landslide dam there with a pond about 75 meters long,
but that had breached by the time that they had flown over it.
So this map here shows kind of the overview of all of the landslides
that we mapped and the ones that we flagged of potential concern.
So the flagged ones are shown with red triangles.
And those include some landslide dams with ponding, but also some
that are close to populated areas and close to roads.
You can see we also flagged lots of other landslides as landslide dams in
yellow and road hazards in purple that we did not flag as of potential concern.
But interestingly, even though most landslides were in the west,
a lot of the flagged landslides were in the eastern 2/3 of the affected area,
which is also where more people happen to live.
So it’s pretty difficult to assess human impacts from satellite imagery,
so we do know from news reports that there was undoubtedly a large toll
due to the landslides triggered by this earthquake.
There were definitely some fatalities, and a lot of people lost their livelihoods,
lots their farms, lost their buildings, and so on.
But only some of this is really visible in the satellite imagery,
like the example at right here. So one way to just roughly estimate
where the human impacts were greatest is to basically find the landslides that
have populations living near them. So this plot here is showing landslides
that have more than 50 people within a 200-meter radius of the landslide.
So it’s just a proxy for human impacts, but this kind of shows that the human
impacts – even though most landslides were in the west, actually most of
the human impacts were probably more towards the center
and the eastern parts of the affected area.
So the human impacts from this event from the landslides triggered by –
you know, may not be over. And one of the reasons is because
of these cascading hazards. So one of them that I’ve mentioned
a few times is the landslide dams. And there were quite a few landslide
dams formed by this event. And we know there were at least 20 that have
observed pooling behind them. And these can catastrophically fail,
and that can cause flooding – rapid flooding without warning
downstream if these aren’t monitored.
And so this is one ongoing hazard to keep an eye on.
And then, as I alluded to earlier as well, a lot of these channels, especially in
Pic Macaya, but also elsewhere, are just filled with sediment from
these landslides now. And so that really changes how the river behaves,
and it can increase not only flooding risk by changing how the water flows,
but also this debris can be mobilized into debris flows, and that can reach
areas downstream and can cause damage and other problems.
And so we didn’t do any, like, sophisticated modeling or anything,
but this plot here is just basically taking the river network and
showing the areas that have the most landslides along them.
So the areas of river with the most sedimentation.
And so you can see that, you know, the western third is probably the highest
area of concern, but there’s actually, you know, channels in the
eastern 2/3 that may also have increased debris flow
and flooding hazards for the years to come.
So, as you all know, there was a major earthquake in 2010 in Haiti
that was further east, and that also triggered a lot of landslides.
And so this is just a quick comparison between the two.
It’s difficult to compare them directly because we have a research-grade
inventory of almost 24,000 landslides mapped for the 2010 earthquake,
and we don’t have that yet for the 2021 earthquake.
But, to more directly compare them, I’m showing just the large landslides
from the 2010 inventory at the right compared to
our inventory from the 2021 earthquake.
You can see that they’re, you know, fairly similar in number when you
consider only the large landslides, and so they’re pretty similar, you know,
earthquake-triggered landslide events, except you can see that the
2021 event is – kind of has areas of higher concentrations
of landslides than the 2020 earthquake did.
So, in conclusion, the 2021 Haiti earthquake was a major
landslide-triggering event, and it had substantial human impacts.
And basically, the hazard outlook in the region has been changed
because of these landslides, likely for years to come.
We found that sharing information in these daily reports with the
humanitarian groups and aid agencies was really important, and especially
writing those in plain English were really useful, and we really
benefited because Stephen Slaughter, one of the co-authors of this work,
is half employed by USAID. And so he’s kind of embedded with them,
and that made it a lot easier to share information.
We also saw that, you know, there’s a lot that you can learn
from a remote response, but it really leaves a lot to be desired because
you don’t really know exactly what’s going on a lot of the time.
You really need field investigations, and I know that some Haitian
colleagues and also a team organized by the Geotechnical Extreme Events
Reconnaissance group have been doing some additional field investigations.
And then I also hope that you see how the near-real-time ground failure
products that are now available can be used to kind of help inform what
happens right after an earthquake.
And so, with that, I’ll conclude and I’ll take any questions.