Monday, June 12, 2023

Why does smooth pāhoehoe lava suddenly change to crystal-filled ‘a’ā lava? A new theory.

 When water flows down a gradual stream over a generally flat bottom, it’s clear and transparent, but when it hits a steep slope like rapids and waterfalls, it turns white and frothy.

Still wet, but very different.

Similarly, newly-erupted molten volcanic rock flows smooth and sinuous as pāhoehoe lava, and then sometimes changes to an entirely different look, broken-up, chunky, rough ‘a’ā lava.

We know what’s causing the water to change—turbulence and increased speed. But what’s happening with molten rock?

A team of Stanford researchers think they have an answer. They are Cansu Culha, Sam Spinner and Jenny Suckale, and in May 2023 Geophysical Research Letters published their theory under the title, “The Yih Instability in Layered Lava Flow May Initiate the Pāhoehoe to ‘a‘ā Lava Transition.”

You find both kinds of lava at volcanoes everywhere there are basalt-erupting volcanoes, whether the Hawaiian volcanoes or those erupting through the snows of Iceland.

Most lava flows start as pāhoehoe, and then occasionally some of them suddenly change form. Instead of flowing like water down a quiet river, they change dramatically. You can even hear the change, as the ‘a’ā tinkles and pings like broken glass as it tumbles rather than flows downslope. And ‘a’ā has far more crystals in it.

The change in form, the authors write, is a big deal to volcano scientists: “These fundamental differences in flow characteristics have made understanding the transition a classic question in volcanology.”

Others have suggested that turbulence may be a factor, that if you stir up pāhoehoe, it will change to ‘a’ā. 

But how does that happen? How does smooth, internally blended lava change to rough crystalline lava?

The authors looked to the work of Chia-Shun Yih, who in 1967 wrote a seminal paper on fluid dynamics. Yih noted that when there are different viscosities in a moving liquid—meaning they flow more or less easily—that can cause instability in the fluid. That concept is now called Yih Instability.

When a lava flow starts as pāhoehoe, over time, the surface is exposed to cooler air and starts to harden. And so, soon, there is molten rock flowing at different rates of speed within the same flow.

“A key assumption in our model is that pāhoehoe flows may have internal layers,” the authors write.

And that difference between layers can cause instability, which can provoke the change from smooth lava to rough chunky lava, they propose.

But it’s complicated.

Sometimes a change in speed can prompt ‘a’ā transformation, like when pahoehoe flows over a cliff. But not always.

Sometimes just a fast-moving flow down a steep slope can prompt the change. But not always.

And sometimes, a hardened surface appears to protect the still-moving lava below from making the change. That might be what happens in a lava tube—when the surface has hardened over, and the pahoehoe lava beneath can flow long and fast without the internal viscosity layers.

With Kīlauea erupting again, the new suggestions provide volcano scientists with new ways of looking at what’s going on.

If you’re interested in a less complex review of the data than is in the Geophysical Research Letters piece, Maya Wei-Hass has a review in the journal Science, under the title “Lava comes in two flavors…”

© Jan TenBruggencate 2023

Monday, May 29, 2023

Hawai'i ocean levels inches below normal--what's going on?

 Sea levels around Hawai’i are unusually low, and have been for some months.

Experts aren’t sure why. They are pretty sure they’ll come back to normal, and higher. But because they’re not sure precisely why, they also can’t be sure when.

My canoe paddling clan in recent month has noticed that low tides have seemed really low. Like, mud flats where there’s normally water. Others may be seeing reefs where there's normally water. And seeing beaches bigger than they were last year.

To figure this out, I called Chip Fletcher, who didn’t know, but knew who would. Fletcher is the interim dean at the University of Hawai’i Mānoa School of Ocean and Earth Science and Technology. He’s the go-to guy on impacts of sea level rise in the Islands.

He suggested calling the university’s Sea Level Center, where associate director Matthew Widlandsky confirmed what we’d been seeing.

“You are right about the sea levels this year around Hawaii being lower than in recent years,” he wrote.

But while he and his colleagues have a theory about the reasons, nobody’s actually gone out and done the work to prove them. “We have not yet studied this event in detail,” Widlansky said.

One theory is that it’s associated with cooler water in the central Pacific, in connection with our just-ended three-year La Niña. Cooler water is denser, meaning it takes up less volume.

One of the several drivers of sea level rise is warmer water expanding, and this would be the reverse, a temporary situation in which cool water contracts.

But there might be more to it than just that.

We’ve experienced this kind of condition before in connection with El Niño (warm conditions) and La Niña (cooler conditions) climate cycles. A study in 2020 reviewed a 2017 period when we were having super-high tides.

Widlansky was a co-author of an article on that study, published in the Journal of Climate. Other authors were Xiaoyu Long, Fabian Schloesser, Philip R. Thompson, H. Annamalai, Mark A. Merrifield and Hyang Yoon.

“Hawaii experienced record-high sea levels during 2017, which followed the 2015 strong El Niño and coincided with weak trade winds in the tropical northeastern Pacific,” the authors wrote.

“During August 2017, the Honolulu Harbor tide gauge recorded the highest monthly average water level since records began in 1905.” That record was 17 centimeters, or more than half a foot higher than expected.

That said, high sea levels don’t always follow strong El Niño events, and didn’t after the strong 1997 event. So there’s something else also going on. Maybe winds. Maybe other stuff.

“The processes controlling whether Hawaii sea levels rise after El Niño have so far remained unknown,” they wrote.

In 2017, "the high sea levels were caused by the superposition, or stacking, of multiple contributions.”

The high sea levels associated with the 2015 strong El Niño lasted from 2016 until the end of summer in 2017, and then tapered off.

The current low water is just a couple of inches lower than normal, and it's different in different locations. 

It is not clear how long the current low stand of Hawaiian water will last. 

© Jan TenBruggencate 2023

Saturday, May 20, 2023

Gray-backed tern returns to Palmyra Atoll

 The Nature Conservancy has attracted gray-backed terns back to Palmyra Atoll after they were lost to the island, likely due to rat predation.

(Image: Gray-backed tern chick. Credit: The Nature Conservancy.)

Researchers used wooden decoys and recorded bird calls to try to convince the terns--and seven other seabird species--to land and to nest on Palmyra. A single gray-backed tern was raised on this island this season, the first in recent memory.

Gray-backed terns, formerly Sterna lunata and recently recategorized Onychoprion lunata, are pākalakala in Hawaiian. They are one of eight seabirds known to the part of the ocean that contains Palmyra, but which have not been found nesting there in recent years. They likely were preyed on and their breeding colonies removed by rats that came during World War II.

Rats were eradicated from the island in 2011. In 2020, The Nature Conservancy began trying to call the missing seabirds back to the island with loudspeakers playing recorded nesting calls, and with wooden bird decoys. These techniques have successfully called in birds in other projects.

Gray-backed terns are the first to respond.

These birds are speckled as chicks--as shown in the photo above--but as adults they have white bottomsides, gray backs, and a black head with a white stripe over the eye. 

Palmyra Atoll, roughly 900 miles south of Hawai'i, is jointly managed by The Nature Conservancy and the U.S. Fish and Wildlife Service. 

© Jan TenBruggencate 2023


Tuesday, March 21, 2023

I guess it's possible to be optimistic about the new IPCC report, and some are. I'm not.

The newest United Nations report on planetary climate, different from previous cautious reports, minces few words. 

Things are getting worse, and faster than ever, and we have no time left to act. Paraphrasing Yoda, it's time to do something; simply trying is not an option.

“The report is a full-throated call for the massive—yet doable—changes our species must enact to limit the damage that comes with each fraction of a degree of warming,” said Wired, the online magazine. 

There is now more carbon dioxide in the atmosphere, 410 parts per million, than in the past 2 million years—that’s before there were humans on our planet. No other period in the past 2,000 years has seen climate warming as fast as in the past 50 years.

The impacts of these changes have been seriously inequitable. The Intergovernmental Panel on Climate Change 2023 report says the people least responsible for the change are suffering the most.

“Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred. Human-caused climate change is already affecting many weather and climate extremes in every region across the globe. This has led to widespread adverse impacts and related losses and damages to nature and people. Vulnerable communities who have historically contributed the least to current climate change are disproportionately affected,” the report said in its summary for policymakers.

You can find the actual report summary and various associated documents here

Nearly half the world’s population is vulnerable and at risk of climate change disruptions, from coastal inundation, storms, flooding, drought, food and water shortages, and related issues. That risk is playing out now, and continues to increase.

“Between 2010 and 2020, human mortality from floods, droughts and storms was 15 times higher in highly vulnerable regions, compared to regions with very low vulnerability,” the report said.

The already-observed changes include water shortages, crop failures, livestock health problems, reduced fishery yields, malnutrition, infectious diseases, community displacement, and immense impacts on ecosystems. The report cites throughout how much faith it has in its observations.

“Climate change has caused substantial damages, and increasingly irreversible losses, in terrestrial, freshwater, cryospheric, and coastal and open ocean ecosystems (high confidence). Hundreds of local losses of species have been driven by increases in the magnitude of heat extremes (high confidence) with mass mortality events recorded on land and in the ocean (very high confidence). Impacts on some ecosystems are approaching irreversibility such as the impacts of hydrological changes resulting from the retreat of glaciers, or the changes in some mountain (medium confidence) and Arctic ecosystems driven by permafrost thaw (high confidence.)”

As we move along in time, it gets worse. “Every increment of global warming will intensify multiple and concurrent hazards.”

There are two primary options: Mitigation, or doing something about it; and adaptation, or learning to live with it.

The report says we have the technology to mitigate, to turn things around. But it would take severe and dramatic action. We do not seem to be willing as a planet to do what’s necessary.

“Deep, rapid, and sustained reductions in greenhouse gas emissions would lead to a discernible slowdown in global warming within around two decades, and also to discernible changes in atmospheric composition within a few years.”

But we are not spending enough money on it, and not committing enough of our policy initiatives to it.

So what about adapting? Realistically, even with drastic action, things would get worse before the arrow of livability starts to turn upward. So some adaption will be required anyway.

Clearly the poorest among us will be hit soonest and hardest, and they will have the fewest opportunities to adapt. The wealthier communities will be able to adapt, to a degree. But increasing climate change will threaten even their adaptation options.

“Adaptation options that are feasible and effective today will become constrained and less effective with increasing global warming. With increasing global warming, losses and damages will increase and additional human and natural systems will reach adaptation limits,” the report said.

To avoid catastrophe, the report says, the world needs immediate and severe cuts in greenhouse gas emissions. To limit the worst impacts in the coming few decades, emissions need to be driven to near zero.

But policies currently in place don’t do that. If anything, they leave emissions flat, meaning the situation continues to get worse.

This is the frustration. We can do it. We must do it.  But it is not clear we will do it.

What are the odds that this particular planet can galvanize its systems to do what the IPCC says is required? Here is the IPCC’s vision:

“Effective climate action is enabled by political commitment, well-aligned multilevel governance, institutional frameworks, laws, policies and strategies and enhanced access to finance and technology. Clear goals, coordination across multiple policy domains, and inclusive governance processes facilitate effective climate action. Regulatory and economic instruments can support deep emissions reductions and climate resilience if scaled up and applied widely. Climate resilient development benefits from drawing on diverse knowledge.”

Lots of media reports—ignoring the essence of the report—are all about the upside: “We can fix this! Yes, we can!”

The Christian Science Monitor takes the middle path, noting that the IPCC “walks a fine line between desperation and hope in an effort to spur a more forceful global response.”

Some publications get lost in the weeds. CNBC decided to focus on reflecting the sun's light and heat back into space. Others wondered whether carbon capture technology is ready for prime time.  

All the while ignoring the elephant in the room--we need to stop burning oil and coal.

So, the thinking goes, maybe we can do these interesting techie things, and keep on burning coal in power plants and gasoline in our big luxury cars. And everything will be just fine.

That, of course, is dithering. And while dithering, perhaps we can ponder this: 

How much misery are we willing to subject our grandchildren and their grandchildren to, to keep living the way we are living?

© Jan TenBruggencate 2023 

Friday, March 10, 2023

Climate shifts further: La Niño is over, El Niño coming by summer

The La Nina oceanic condition, which we’ve been in for many months, has ended, and an El Nino appears likely to form in the summer or fall.

That’s the latest prediction from the Climate Prediction Center: 

It builds on the report we filed last month, when we suggested a fair chance of El Nino by mid year. That fair chance now seems to have been elevated to a pretty good chance. Spring predictions tend to be problematic, but most models see us going that way.

Thus the La Nina cool phase of Central Pacific climate is behind us, and we are in something called ENSO-neutral, ENSO being the term for the whole warm-cold cycle, El Niño Southern Oscillation.

Most climate prediction models now suggest we should shift into El Niño during the summer, and it might happen pretty quickly: “it is possible that strong warming near South America may portend a more rapid evolution toward El Niño.”

One of the things that can mean for Hawai’i is that we are likely to have a more active hurricane season. Also some other changes. More on that a little further down.

But one the questions that still challenges climate researchers is where climate change is taking the ENSO pattern broadly. There’s some suggestion that the past 40 years—since 1980—have been a little cooler than expected, a little more La Niña.

Now, many researchers say their models suggest the next few decades may swing toward more active El Niño conditions. But they don’t fully trust those models: the computer climate models of past climate don’t match up real will with actual observations of the climate. So how to be sure? A whole lot of smart people are working hard to make sense of that.  A discussion on this can be found at the ENSO blog

Among the variables: Warmer oceans can feed circulating storms, but warmer oceans and changing wind conditions can also cause changes in deep ocean upwellings. If they bring cool water to the surface from the deep ocean, then that could reduce the energy available to circulating storms like hurricanes. Changes in cloud cover could also create cooler surface conditions. And there are other variables.

“Heroic efforts are being done at modeling centers around the world to improve the representation of the physical processes,” wrote Kris Karnauskas, of the University of Colorado-Boulder.

That’s the long term.

For the coming year, what does an El Niño mean for us? There’s a nice NOAA fact sheet here. 

It suggests wetter weather at first, in late summer and fall, then drier. Maybe a dry winter this year. Weaker trade winds. More hurricanes and tropical storms. Warmer water around the Islands.

And sea levels slightly higher than normal, meaning big storm surf will reach farther inland.

All in all, interesting times.

© Jan TenBruggencate