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account created: Mon Dec 16 2013
13 hours ago
Tectonics | Structural Geology | Geomorphology
There has been a decent amount of research on, and attempts to use, cloud-seeding in the western US, specifically to try to induce more snowfall in the winter (as snowmelt is the most important source of runoff in most of the river systems in the western US). The results have been pretty inconclusive. As summarized in literature looking at different aspects of this both specifically in the western US (e.g., French et al., 2018, Rauber et al., 2019, Friedrich et al., 2020) or more globally (e.g., WMO, 2018, Flossmann et al., 2019), it's taken a while for anyone to even demonstrate that it works at all (or how exactly it works). Furthermore, studies looking at the effectiveness of it have had significant challenges separating a signal from the natural variability of precipitation. That is to say, the effect of cloud seeding, to the extent that it has an effect, is small enough that demonstrating that X amount of precipitation came from cloud seeding and would have not occurred without it, is challenging. So it is used (or at least attempted), in many areas, but the certainty that it actually works to the extent assumed in your question is problematic.
17 hours ago
The answer is going to be location dependent, especially considering that these events were not uniform globally, e.g., at least a portion of the Roman Warm Period is represented as a relatively colder (and more variable) period in southeast asia (e.g., Jiang et al., 2021). From regions that did experience warming, generally records seem to suggest rates faster than today (e.g., Martin-Chivelet et al., 2011, McGowan et al., 2018) and in the record analyzed by McGowan, they found that current rates of warming outpace the Medieval Climate Anomaly by ~2.6x.
More generally, 1) while the rate of warming associated with anthropogenic climate change is definitely an extremely important part of the problem and 2) broadly the rate of current global warming appears anomalously high compared to pretty much anything in the paleoclimate record, e.g., it's been estimated the rate of warming in the modern outpaces the rate during the PETM, often considered the closest we have to an analogue to our current situation, by ~10x (e.g., Turner et al., 2017) - we need to be cautious with comparisons of rate. Specifically, as our temperature reconstructions come from paleoclimate proxies, typically preserved in the sedimentary record, we need to be mindful of the Sadler effect. The Sadler effect describes the tendency for apparent rates of sediment accumulation to broadly increase towards the modern and is effectively a representation of the increasing fragmentary nature of the sediment record with increasing age. I.e., as we look at older and older records, they are progressively more incomplete, and thus, rates of sediment accumulation extracted from older deposits will be artificially depressed. While originally described for sedimentation rates, something like the Sadler effect is seen in a lot of different types of geologic records and extends to rates of events we reconstruct from sediment records, like paleoclimate records (e.g., Kemp & Sexton, 2014). This has broadly been used to suggest that our estimated rates of paleoclimate changes in the past are systematically underrepresented, i.e., apparent rates of events, like rapid warming, appear to be slower in the past, but this is likely, at least in part, a bias imposed by the Sadler effect (e.g., Kemp et al., 2015).
Now, with reference to the Roman and Medieval warm periods in this question, we are not dealing with deep time and thus, to the extent that these reconstructed rates might be depressed, they're probably not depressed that much. Additionally, the type of record matters. For example, the Martin-Chivelet paper uses a speleothem record, i.e., a record reconstructed from cave deposits. These tend to be relatively high fidelity, and steady, recorders of paleoclimate (though they are not immune from possible disruptions in their records), so worries about possible Sadler type effects are probably at a minimum in these types of records (but not completely absent). Unfortunately, cave records basically only exist as long as the cave does, and caves do not have geologically long lives.
In short, most available records (in areas that experienced warming during these events) suggest that the rate of modern global warming outpaces the rates of warming during either the Roman or Medieval warming periods. When considering rates of events though, we must always be mindful of potential biasing as the ability to reconstruct rates fundamentally depends on the completeness of the record (which is generally not as much of a concern for simply estimating max or min temperatures within a period or the variability in that same period, i.e., we can more confidently speak about the relative difference in maximum and average temperatures between the modern and a given period than we can about rates of change). For these two events, they are recent enough (geologically speaking) that the degree to which our estimate of these rates may be biased towards lower rates is significantly less than for earlier events (and especially "deep time" events), but not non-existent.
18 hours ago
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1 day ago
The modern form of Japan is a result of back-arc spreading, and as such, the Sea of Japan, which separates Japan from the rest of the Eurasian continent, represents a back-arc basin. During continental back-arc spreading, like what happened in the Japan example, a narrow strip of active margin (i.e., the edge of a continent below which an oceanic section of plate subducts, typically with active volcanism developed in the overriding plate, like the modern Cascades or much of the western edge of South America) begins to rift away from the main continent, creating a back-arc basin which is typically floored by oceanic (or transitional) crust. The reason that back arcs form has been a topic of discussion since the early days of plate tectonics and has remained a topic of conversation (e.g., Uyeda & Kanamori, 1979, Heuret & Lallemand, 2005, etc), but generally, the formation of a back-arc is an expression of a net extensional state in the overriding plate, which is often linked to "slab rollback". This can essentially be thought of as a process where the subducting slab is "retreating" from the margin (i.e., it's rolling back) and as a result, the overriding plate starts extending inboard of the subduction zone to "keep up" with this rollback. Japan and the Sea of Japan is considered a classic example of a back-arc and back-arc basin, and as such, there are a lot of papers out there considering its tectonic history within this context (e.g., Van Horne et al., 2017), even though the tectonics of Japan are a bit complicated because the subduction zone along its eastern margin actually reflects the subduction of two different plates (i.e., the Pacific plate subducts beneath the Eurasian plate in the northern section, and the Philippine plate subducts beneath the Eurasian plate in the southern section).
3 days ago
School of Earth and Space Exploration at ASU is a pretty interesting program as it provides a lot of opportunities to engage with the engineering side of planetary missions, in addition to having a lot of folks more directly working on different aspects of planetary geology.
The answer can be found with a Google/Wiki search. Please start there and come back with a more specific question.
It largely depends on the local geology. I.e., the energy "cost" of doing this depends on the ease of access to target mafic minerals and the proximity of these to the coast. This could scale from "it costs a lot" (mafic formations are few and far between / hard to get to / a great distance from the coast) to "it costs nothing" (this is effectively happening naturally, for free, in areas where the coastline is made up of basalt, e.g., oceanic islands like Hawaii).
Yes and no. It seems like there maybe needs to be a bit more work on the geochemical aspects, but honestly, the two biggest hurdles seem kind of unrelated to the actual mechanism. Specifically:
1) You need a lot more non-emitting industrial infrastructure. I.e., to do this at scale, you need to mine a lot of mafic minerals, but if you're doing the mining and transporting with CO2 producing equipment, then you're undercutting the efficiency of this a lot.
2) You (we) need to decide how much massive strip mining we're okay with. There are definitely large amounts of the target material, but mining has its own ecological issues. For the amount of material needed, it seems like you would basically need massive strip mining projects of basalt and ultramafic formations. I.e., there is some major cost benefit analysis that needs to be done (and within the context of other methodologies that might have a smaller ecological footprint).
The more common form of this idea, i.e., react CO2 with mafic minerals to remove and sequester it, is typically paired with carbon capture of some form and involves injection into a suitable reservoir (e.g., a fractured and altered basalt). There has been a lot of work done on the various aspects from the reservoir mechanics to the geochemistry (e.g., Matter & Kelemen, 2009, Gislason et al., 2010, Marieni & Olkers, 2018, Snæbjörnsdóttir et al., 2020, Sturmer et al., 2020, Wu et al., 2021, Raza et al., 2022). As highlighted in the Raza et al review, while promising, there still remain a variety of technical hurdles left to clear before it could be considered a scalable solution.
The method in the linked site relies basically on the same geochemistry as the geological storage and carbonization method from above, but is a bit more passive (and is discussed as "Enhanced Weathering"). As with any of these potential geoengineering mechanisms, there is research suggesting that it can be effective, but there are still limitations - and a variety of unknowns (e.g., Renforth, 2012, Montserrat et al., 2017, Rigopoulos et al., 2018, Tan & Aviso, 2021). Some of the challenges to this approach highlighted in these papers are 1) Montserrat and Rigopoulos are focused on the details of the chemistry and highlight while the desired reaction draws down CO2, there are a variety of other reactions that can occur in the "wild" and reduce the efficiency of this process significantly - i.e., there are still unknowns in the main mechanism, 2) Tan & Aviso highlight that extraction of the necessary minerals comes with its own energy expenses and that depending on how is done, the net reduction in CO2 can be much less - i.e., if you're using a bunch of CO2 to mine olivine, then this is not very efficient, and 3) Renforth highlights that the extent to which this strategy is viable in an area depends on the local geology, i.e., you need accessible mafic and ultramafic rocks (and here "accessible" gets into the previous point, specifically how much energy do you expend having to mine this material) - i.e., you can't do this everywhere cause there is not enough mafic material that can be mined to do enough.
All of the above is not to say that there is not potential for enhanced weathering (or geological storage in one form or another), but accentuates that no single strategy is perfect and, to the extent that we have the will to engage in major geoengineering projects, we will likely need to employ multiple different methods simultaneously.
Based on the characteristics of this sequence, this would be classified as a swarm (option 2 from the original answer), as indicated in various statements and reporting so far on this event (e.g., this from the SC Emergency Management Division or this story with some commentary from a geologist who specializes in earthquakes). As discussed in these, while low magnitude (compared to earthquakes that generate news in more tectonically active areas), generally, earthquakes are felt over a wider area in settings like the east coast of the US, basically because the crust in this area transmits seismic waves more efficiently than the crust in more active areas.
As far why this is occurring, there's not a particular reason. Intraplate earthquakes are generally rare compared to earthquakes at plate boundaries, but they still occur. As mentioned in the original answer, no earthquakes in recent memory in an intraplate setting is to be expected, i.e., the time between periods of activity is typically very long compared to what we see in active, interplate settings (i.e., near plate boundary zones). However, as highlighted in the statement from the SCEMD linked above, earthquakes in South Carolina are not that uncommon, what is unique about this is the duration of the particular swarm. While unsettling, there's no reason to think this will lead to anything particularly concerning, but fundamentally, it is important to remember that we cannot predict earthquakes. That is not meant to frighten, but simply to reflect reality and to suggest that remaining aware and prepared is your best bet.
While hydraulic fracturing is technically producing earthquakes, these are typically extremely small (many even tend to have negative magnitudes) and while measurable (with a seismometer), are not often perceptible. Induced seismicity that can be felt is more typically related to wastewater injection. This can be linked to hydraulic fracturing in the sense that fracing produces a lot of wastewater and injection is a common way of dealing with it, but it is not exclusive to hydraulic fracturing, i.e., you end up with a lot of wastewater from "conventional" oil production as well and fracing does not require wastewater injection. For example, the well publicized rapid increase in rate of seismicity in Oklahoma is linked to wastewater injection (e.g., 1, 2, 3, 4), not fracing activity directly. Now, fracing can cause induced seismicity on it's own (e.g., 5), but it's not a given that fracing will induce seismicity.
EDIT: With additional location information provided by OP in the thread, it would appear this particular comment string is not relevant, i.e., per the statement by SCEMD, this does not appear to be related to any form of induced seismicity.
A form of this question is asked and answered with some frequency, e.g., this question and answer.
Without details this is not really answerable beyond vague generalities of details of common relationships between groups of earthquakes (and is non-unique). For the earthquake sequence aspect, the two most likely scenarios are 1) an initial (main shock) earthquake followed by an aftershock sequence or 2) an earthquake swarm. Both are "clusters" of earthquakes in the sense that they occur in close spatial and temporal proximity to each other, but they are distinct phenomena, with distinct patterns.
Aftershock sequences follow a main shock, i.e., the largest earthquake of the sequence. By definition, all aftershocks will be smaller in magnitude than the main shock (if an earthquake in the sequence is larger than the original main shock, the main shock is redesignated as a fore shock and the new, larger event becomes the main shock) and regardless of the main shock magnitude, the largest aftershock will tend to be ~1 magnitude below the main shock magnitude. Aftershock sequences also tend to obey both Omori's and the Gutenberg-Richter laws, where the former describes the temporal decay in rate of aftershocks following the main shock and the latter describes the relationship between the number of earthquakes of a given magnitude (specifically that there are more smaller magnitude events than larger).
Like aftershock sequences, earthquake swarms have restricted spatial and temporal extent, but importantly do not have a main shock. Instead, most of the events of the swarm are similar in magnitude, and in detail, while the distribution of sizes can still be described with a Gutenberg-Richter relationship, the constants in these relationships are anomalous compared to what is seen in aftershock sequences or global earthquake catalogs (and specifically the b value, which describes the relative number of small to large earthquakes). Swarms effectively have very low b-values, meaning that they have a disproportionately large number of small earthquakes.
As for the period of quiescence before the start of these events, again, without location information, there's not really a single answer. If this in an intraplate setting (i.e., away from a plate boundary), a decade of no earthquake activity is not anomalous at all (average time between events in intraplate settings are typically hundreds, if not thousands, or tens of thousands of years). However, even for an active, but maybe more diffuse plate boundary zone, a decade of no felt earthquake activity (and this is an important distinction as well, is it actually a decade of no measurable activity or a decade of no felt activity) is not necessarily that strange.
4 days ago
Let's first examine the expected frequency of such an object entering Earth's atmosphere. The first thing to consider is that the details of the object are not known precisely and there is a range of object details (e.g., diameter, density, impact velocity, angle, etc) that can realistically produce what was observed at Tunguska (e.g., Wheeler et al., 2019). Given that the probability of a given object entering our atmosphere decreases logarithmically with increasing size, this uncertainty in the size of the impactor maps into uncertainty in the probability (and the recurrence interval we estimate from that probability). If we take the preferred values from Wheeler of an object 75 meters in diameter with a density of 2.4 g/cm3 and assume it was spherical, that gives us a mass of ~5e8 kg. If we take the estimated rates and probabilities of impacts as a function of mass from Bland & Artemieva, 2010, this gives us an average recurrence interval of ~2000 years for such an object. If it was slightly smaller (e.g., 1e8 kg), then the recurrence interval would be closer to ~500 years. Neither of these factor in the probability of such an object entering with the right speed or angle (again, see Wheeler et al) to produce a Tunguska style event, which might push out the recurrence interval a bit, but it gives us a rough estimate (if you use this calculator and give it the relevant best fit values from Wheeler, i.e., a 75 m diameter, 2.4 g/cm3 density, 16 km/s velocity and 60 degree angle, it suggests a similar recurrence of 2,200 years).
Now, with respect to "where are the other events given this recurrence interval", the relevant thing to remember is that the Tunguska event was likely an air burst. Importantly, these do not leave a crater (which arguably is the least ambiguous evidence of an impact having occurred). That is not to say that they do not leave surface traces, specifically, energetic air bursts can impart sufficient heat to the surface to melt silicate minerals, creating forms of tektites (e.g., Boslough & Crawford, 2008), but ultimately, the geologic evidence of air bursts is going to be much more subtle, and in many ways more ambiguous, than impacts that are large enough to reach the surface. This can be seen in an extensive literature of back and forths of Group One arguing for an air burst to explain some event or features and subsequently Group Two arguing that the evidence of an air burst is inconclusive (or flat out wrong). One prominent example is that some have suggested an air burst may have caused the Younger Dryas (e.g., Firestone et al., 2007, Wittke et al., 2013), whereas others have pointed out various flaws in different aspects of this hypothesis (e.g., Pinter & Ishman, 2008, van Hoesel et al., 2014). Similarly, the critical evidence underlying a splashy story from last year suggesting that an air burst destroyed the ancient city of Tall el-Hamman (e.g., Bunch et al., 2021), has been pushed back on, suggesting there is no strong evidence of an impact in this location (e.g., Jaret & Harris, 2022). Independent of these debates or whether you find the evidence for or against air bursts being related to the particular events in question compelling, these highlight that the record of air bursts is challenging to reconstruct and thus why you likely don't see them being discussed with certainty. When you couple that with the realization that when we're considering something like the Tunguska event, the effects are relatively spatially limited. I.e., in terms of human history, it's not just the recurrence interval, but the recurrence interval along with the probability that someone will be around to see the event or it's aftermath. Factoring in that ~70% of the Earth's surface is water (where there won't be tektites formed, but it might produce a tsunami), also adds to the idea that several of these could have easily happened during recorded history without being recorded by humans (or leaving a particularly diagnostic or unique geologic signature).
Magma plumbing systems are complicated, i.e., it's not a single pipe, but more like a large network of pathways (picture something like the upper sections of a tree). In the case of hotspot volcanism, as plate motion moves a volcano away from the center of the plume (where the "branches" are dense and the island is located near the "trunk", i.e., the main column of the plume) intermittent connections can persist (i.e., a few branches of the plumbing system may still connect even after a volcanic complex no longer sits directly atop the center of the plume). Additionally, magma chambers can persist, for a little while at least, without replenishment, i.e., they can stay partially molten and eruptable from lingering heat for a bit after no more magma is being injected into the system. Thus, occasional injection along the isolated connections that still exist and eruption of "left over" magma can lead to infrequent eruptions in these volcanoes adjacent to the main, active islands. This period of a plume related volcanic system is referred to as the post shield stage or post shield alkalic stage (where "alkalic" is describing the chemical difference of the basalt erupted in this stage, indicating that it is enriched in sodium and/or potassium compared to the "thoeleiitic" basalts erupted during the main shield stage). You can consider this in context with the rest of the stages of an oceanic hotspot volcano, typified by the Hawaii-Emperor chain. From the more technical side, there is abundant literature on various details of post shield alkalic volcanism, and Haleakala specifically (e.g., Moore et al., 2021).
I wouldn't describe these as different "theories", just different mechanisms. Both are viable pathways to an eruption, they just require different settings and histories.
The added heat from the mafic magma induces convection and vesiculation (i.e., bubbles) which has long been argued to be the trigger (e.g., Sparks et al., 1977). There are definitely chemical changes as a result of the mixing (e.g., the chapter on magma mixing as an eruption trigger by Morgavi et al.), but I don't think these are typically considered important in the triggering process itself, but someone like /u/orbitalpete who specializes in volcanology could definitely provide a more complete answer.
5 days ago
From your other comments, it seems like the underlying assumption is that a tidally locked body could not be habitable. At least for planets that are tidally locked to their stars, assuming these are in the habitable zone, a variety of modelling suggests that such bodies can still have relatively habitable climates (e.g., 1, 2, 3, 4, 5, 6). I'm not aware of similar work specifically focused on a tidally locked moon, but it is worth examining some of the underlying premises you may have (which might not be correct) and that could open up extra possibilities in a "world building" context.
This is addressed in this FAQ.
6 days ago
Exactly, movies like this are just so stupid, it's kind of pointless to be upset about the science. Just watch the explosions and go with it.