Virginia combined temperatures

This is a continuation of the series where I look at the temperatures recorded for an individual state, over the past 115 years, and see what that data tells us. Moving on from West Virginia which I covered last, to Virginia returns me to the Atlantic coast, and a certain curiosity as to whether the significant drop in temperatures between 1948 and 1965, found in other states further South along the coast, also occurred here. (For the impatient, it does). Virginia has 19 USHCN stations from Blacksburg to Woodstock, and has two GISS stations on the list, at Richmond and Roanoke.

Location of the stations in Virginia (CDIAC )

Unfortunately the CDIAC site still has the problems that I noted last week, when writing about West Virginia and it doesn’t appear possible at the moment to get the data directly from the site, which is an irritant. There are five Richmond sites as supplying data to GISS, though only one, Richmond Byrd, with the correct location, and it has data from 1911. Richmond is relatively close to the coast, and shows the temperature drop I referred to above, reaching a high in 1949, then dropping to a low in 1966.

UPDATE: Browsing Climate Audit, I came to Martin A's suggestion that we should consider the first difference trend for temperatures. I hadn't thought to do that, but since the data is easy to hand, I ran the plot and have added it to the end of the post. As Hu McCulloch noted, it doesn't seem to add much to the information on the state temperatures, having just about averaged out over the century. So, with respect, I don't think I'll add it to the repertoire.

Annual temperatures as reported for the GISS station at Richmond, VA.

Roanoke is one of the westernmost stations in the set, and it only has data from 1948, so that although there is a fall in temperatures from the beginning, which bottoms out in 1982, information on the temperatures in the 30’s is missing.

Annual temperatures as reported for the GISS station at Roanoke, VA.

When I combine the temperatures for the state from the USHCN network, and compare this with the average for the two GISS stations, then I get a graph that shows the change in range of the two stations, but that, recognizing that impact, shows that the GISS stations have always shown a higher temperature (by about 2.8 deg F).

Difference between GISS station average temperature and that of the USHCN average temperature per year.

In terms of the overall change in temperatures of the state over the century of data acquisition:

Change in average station temperature with time, for Virginia

There is still that drop in temperature from around 1950 to about 1968, with a consequent pick-up in temperature. Obviously we are no longer in that group of states that lost temperature over the century.

Virginia is 430 miles long and 200 miles wide. It runs from 75.22 deg W to 83.62 deg W, and from 36.52 deg N to 39.62 deg N. The central latitude is 37.49 deg N, that of the USHCN average is 37.7 deg N, and that of the GISS stations is 37.41 deg N.

The elevation in the state runs from sea-level to 1,742 m, with a mean elevation of 290 m. The average elevation of the USHCN stations is 281 m, and for the GISS stations 172 m.

It was a little more difficult to get the information on population for Virginia, since the site names did not easily fit with the source sites that I use. Bremo Bluff did not have a citi-data site, so I used the Zip-code site to find that it was 795. Burkes Garden was a little more of a challenge, with a population of 260 coming after a greater search, though it is 7 miles from Tazewell which has a population of 4,282. Dale Enterprise turns out to be on the outskirts of Harrisonburg (I had to use Google Earth to find that one) Hot Springs is (via Google Earth) actually now in Clifton Forge. Lincoln is near Purcellville, using the same approach; Piemont is in Orange, VA (via Google Earth) And so, ultimately it was possible to get some information on population sizes for all the stations around the state.

Looking therefore at the effects of geography and people on station data for Virginia.

Average station temperature for Virginia as it compares with station latitude.

The correlation is not as good as it normally is, and that may be because of the large variations in elevation within the state. That elevation also influences the apparent correlation with longitude, but remember that this regression line went up on the other side of the mountains in West Virginia.

Average station temperature for Virginia as it compares with station longitude.

The regression coefficient is also much greater with elevation.

Average station temperature for Virginia as it compares with station elevation

Correlating temperature over the past five years with recent population, gives:

Average station temperature for Virginia as it compares with population near the station.

If one were to take out the temperatures pre 1915, the homogenized and TOBS data would have been relatively equivalent until just after 1980 when there is an increase in the homogenized average.



UPDATE: Here is the finite difference plot, i.e. I have plotted the temperature change each year, by subtracting fromt hat annual average the temperature of the previous year, as a function of time. It is for the average of the USHCN TOBS data for the year, and it appears to suggest that, overall, the changes average out - which would suggest there hasn't been that much change in overall temperature, though the plots at the start of the post would suggest a rise of some 1.6 deg F per century.

Change in average Virginia temperature from the previous year, as a function of time.

Katla - perhaps a pause in the development

The recent changes in the earthquake pattern around the caldera of the Katla volcano in Iceland suggest that the eruption that I was anticipating may be somewhat longer in the making than I had stated earlier in the month. The pattern is now diffusing away from the concentrated patterns of quakes that were occurring earlier in the month, although the distribution remains largely close to the initial regions of focus.
Earthquakes around Katla July 13th

Earthquakes around Katla July 18th 2011

Earthquakes around Katla July 23rd 2011

Earthquakes around Katla July 28th 2011

In an earlier post I tried to explain the process that went into the focusing of the quakes in a tighter swarm around a possible eruption site. And for a while this focusing occurred. However, while there was the evidence through the jokulhlaup of some magma penetration that caused glacial melt and the flood that took out the bridge, there has not been any physical evidence on the surface of magma movement since. There have been some harmonic tremors (reported by Jon ) indicative of some magma movement, but no expression of it to the surface.

If we consider that there is a magma chamber under Katla,, Sturkell et al have looked at the evidence of ground swelling to project that this chamber may be around 5 km deep, with up to 700 m of ice in the caldera. They base the location of the chamber on the idea that as the magma flows into the chamber it is under the pressure of the driving fluid that moves it into the chamber, and that this pressure will lift the rock and glacier above the chamber. The pressure is insufficient to break that rock, initially, which is part of the basis for my earlier reasoning that the series of quakes was indicative of the fracturing in the overlying rock, which would weaken the cap and provide passages through it for the magma to flow upwards and thus cause the eruption.

Simplified projected section through Katla after Sturkell et al)

However one thing that does occur as these fractures develop is that some magma may flow into them before they connect a pathway to the surface. In the short term this will lubricate the fractures and ease their growth toward total cap failure. However if the magma is stalled then it is possible that it loses sufficient heat to the surrounding rock that it solidifies. This then becomes the glue that I wrote about in the earlier piece, since it now closes and binds the rock passage walls, so that the cap re-acquires some integrity.

With the possible loss of some pressure with magma escape into the overlying rock, this may then return the situation to a point earlier in fracture development, with the somewhat relieved rock being re-stressed before it will develop a new set of fractures to coalesce, weaken the cap and potentially again raise the risk of eruption. I begin to suspect that we are in this phase at the moment. But, as I said earlier, each case and condition is different and while continued focused quakes in the region of the caldera continue to indicate further weakening of the cap, we do not know how much will be required before an eruption occurs.

Note that the flow of magma under the rock, and the pressure that it exerts, causes the surface of the volcano, and thus of the glacier above it, to move. This movement is monitored using GPS and plots of the data are available.

OGPSS - Gulf of Mexico production, and hurricanes

The summer brings back Hurricane season, with the threat that such storms bring to the oil and gas well operations in the Gulf of Mexico. And the National Oceanic and Atmospheric Administration (NOAA) has noted that

The Atlantic basin is expected to see an above-normal hurricane season this year, according to the seasonal outlook issued by NOAA’s Climate Prediction Center . . . . 3 to 6 major hurricanes (Category 3, 4 or 5; winds of 111 mph or higher)

The lessons of this vulnerability were, perhaps, more than most years, evident in 2005. The first sign of problems came with the arrival of Hurricane Dennis in July. It was a storm which severely damaged the BP deep water Thunder Horse drilling platform.

Thunder Horse after Hurricane Dennis (Prof Goose)

As that season wore on, the vulnerability of the platforms in the Gulf, and the refineries that border it, were exposed in more intensity with the passage of Hurricanes Katrina and Rita. These threats and their analysis were one of the factors that helped, in that formative year, to bring an audience to the pages of The Oil Drum. The Gulf is now home to thousands of wells, which, as the evidence from the Deepwater Horizon disaster last year reminded us, has moved further and further away from shore. That vulnerability is perhaps illustrated by a map, showing the path of Hurricane Rita through the oil platforms off the Texas and Louisiana coasts.

Path of Hurricane Rita through off-shore Gulf production facilities (The Oil Drum) (Each dot is a production unit)

Back in the 1930’s and ‘40’s it was the very gradual deepening of the seabed in the Gulf, that allowed the first oil drillers to venture, through the swampy regions of the Mississippi Delta and then on out into the waters of the Gulf. There had been some drilling from piers out in California and similar constructions were also tried along the Louisiana shore, as the prospects for success tempted companies away from the coast. However, as they did so the rigs faced the challenge, as they do today, of surviving in regions where Hurricanes are not uncommon. The industry was helped in this development since there were no major hurricanes that moved through the regions of most intense drilling, from the first wells in 1945 until 1964 when Hurricane Hilda arrived. And even when that hurricane struck on October 3rd, it only damaged three locations, at Eugene Island and Ship Shoals 149 and 199, with a total of some 11,869 bbl of oil being spilled due to the storm.

Gulf of Mexico showing regional features (Geoexpro)

The first pier-based platform had been built out into the Gulf of Mexico at McFaddin Beach, south of Port Arthur, Texas after having been approved by the Secretary of War, on July 8, 1937. The pier was a mile long, with three rigs at the far end, but it only drilled dry holes and was destroyed in a hurricane in 1938. More widely recognized was the first well to be drilled out of sight of land. This was the Creole platform near Cameron, which was a mile out-to-sea, an hour-an-a-half trip by shrimp boat at the time. The water was only 18 ft deep and the well, initially drilled by Pure Oil and Superior Petroleum, (later Kerr McGee, and then Anadarko) sat some 15-ft above the water level. Initial production was 600 bd from a depth of 9,400 ft. It was damaged by a hurricane in 1940, but survived and produced more than four-million barrels since through directional drilling.

Kemnac Rig 16 drilling the first offshore well in the Gulf of Mexico (Kerr-McGee via Penn Energy)

As was the case with California there was initially some controversy over who owned the rights to minerals off-shore and in 1953 Congress passed the Submerged Lands Act, which gave the rights to the states for the first three miles offshore, (the range of a smooth bore cannon at one time) and then the Outer Continental Shelf Lands Act which gave the rights for the more offshore land to the Federal Government. This settling of the disputes encouraged further drilling and while there were already 70 rigs, drilling at depths up to 70 ft of water, the years after 1953 saw the development of a variety of different rigs for drilling in ever deeper water. Designs to cope with hurricanes also progressed, so that by the time of Hurricane Flossy in 1956 rigs were relatively safe. It was followed by Audrey in 1957, ranked as the sixth deadliest hurricane in US history, which came ashore at Cameron, and killed 416 people, but caused $16 million in damage offshore, with no fatalities.

Path of Hurricane Flossy in September 1956. (Note I have referenced the web pages showing the storm paths under the Hurricane name in that which follows).

Technology was, however, allowing rigs to work in ever deeper water, 100 ft of water in 1957, 225 feet by 1965, and 300 ft in 1969. With this increase in range came increased production, which had reached 2 mbd, but it also exposed more rigs to the threat from larger storms. Hilda, formed in 1964, caused $100 million in damage and effectively destroyed 18 platforms,; Betsy in September 1965 had the distinction of financially impacting a future President of the United States.

On September 9th, the day Hurricane Betsy struck, MAVERICK was located 20 miles off the Louisiana Coast in 220 ft of water. The following day an inspection showed Zapata’s three other rigs were undamaged, but the MAVERICK had vanished. This was the largest single loss that the domestic offshore drilling industry sustained in this or any other hurricane. . . . . .The MAVERICK loss was a substantial one for Zapata. This was our newest rig and one of our very best contracts. . .

(George H.W. Bush, “My Life in Letters and Other Writings.”) (The insurance check was for $5.7 million).

Camille in 1969 was the largest storm to hit the USA in the 20th century. It did about $100 million in offshore damage, including sinking three up-to-date rigs designed to survive those storms. (Camille was a Category 5). Onshore the damage exceeded $1 billion. This was the hurricane that taught the industry that they had to design rigs that could not only withstand waves more than 70-ft high, but has also to consider that the seabed itself might move under the force of the storm.

Fortunately such storms have proved to be relatively rare, and the “three strikes” of Dennis, Katrina and Rita in 2005 have not been repeated since. Yet the industry remains highly vulnerable to such storms. As the second figure shows, the Gulf has become increasingly filled with production platforms. In 2008 this region was hit by hurricanes Gustav at the start of September and Ike two weeks later. Even though these were weaker storms their impact was significant.

Effective August 2008, there were more than 3,800 production platforms in the Gulf, ranging in size from single well caissons in 10 feet of water up to a large, complex facility in 7,000 feet of water. The MMS estimates about 2,127 production platforms were exposed to hurricane conditions from Gustav and Ike, carrying winds greater than 74 miles per hour.

Final results of the agency’s assessment of destroyed and damaged facilities from these two storms indicate that 60 platforms were destroyed. These included some platforms that had been reported earlier to have extensive damage.

In comparison, 115 platforms were destroyed by the Rita-Katrina wallop in 2005.

The platforms designated as destroyed following Gustav and Ike produced 13,657 barrels of oil and 96,490,000 cubic feet of gas per day, or 1.05 percent of the oil and 1.3 percent of the gas produced daily.

Part of the reduction in damage came from lessons learned from Katrina/Rita.

Mobile Offshore Drilling Units (MODUs) that previously had to have eight mooring lines were now required to have 12 and, in some cases, 16 mooring lines,” Angelico said. “In ’08, 18 moored MODUs were in the path of hurricane force winds, and two went adrift, which represented 15 percent of the rigs out there. In Katrina and Rita, 63 percent of the rigs went adrift.’

There are additional impacts from these storms. The Gulf continues to produce about 27% of the nation’s oil, and 15% of the natural gas. Those fuels must be brought ashore and, in the case of oil, refined. Refineries lie inshore all along the Gulf Coast, and if flooded can take months to be brought back on line. Given the growing reliance that the country places on production from these regions makes us all vulnerable to the season.

Outer Continental Shelf (OCS) Crude and Condensate as an annual volume and percentage of national production. (BOEMRE)

Last October OCS crude and condensate production averaged 1.52 mbd, which comprised 28% of the estimated US production.

Offshore Natural gas production as an annual volume and percentage of national production (BOEMRE)

Last October natural gas production averaged 5.6 bcf/day which was 8.9% of estimated national production.

There is a significant production from smaller, older wells, while the new fields are found in deeper waters further into the Gulf, and so that is where I will venture next time.

West Virginia combined temperatures

This series, which has been looking at the temperatures of the different states around the country, is now beginning to approach an initial end, as I look at the data for West Virginia, which IIRC is the last state to complete that does not border on the Atlantic. (Foregoing for the moment looking at Alaska and Hawaii) West Virginia comes after looking at a few states along that littoral, ending last week with North Carolina. One of the features that was clear in those states was that there was a significant drop in temperature around 1950, while on the other side of the mountains, there were a number of states where the temperature has been falling since 1900. It will be interesting to see which of these categories West Virginia falls into.

There are thirteen USHCN stations in West Virginia, and three GISS stations on the list, Beckley which only carried data from 1951, Charleston which only has data from 1949, and Huntington which also only has data since 1948.

Location if the USHCN stations in West Virginia (CDIAC )

In passing it is interesting to note that this is the second week that those going to the USHCN site are faced with this comment:

PLEASE NOTE: CDIAC is currently experiencing hardware/software issues that are affecting the performance of the USHCN web interface.

We hope to have these issues resolved shortly. Accessing data via the FTP area is working normally. We appreciate your patience and understanding. (7/14/2011)

And when I try and access data for the different stations, I cannot. However, having had similar trouble earlier in the summer (starting when I was working on Arkansas in April. That hiatus lasted through Louisiana but was cleared up by the time I got to Wisconsin so that the site was down for about three weeks. This time I had already acquired the West Virginia data, and so the post can proceed.

Taking a quick look at the GISS stations, it is, of course, now no longer possible to see the temperatures in the 1930’s when, until recently, it was recognized that the USA had it’s highest temperatures. Nor is it as easy to monitor for this state the transition from the possible rising temperatures pre-1950 to the possibly falling ones of the 50’s and 60’s.

Temperature change with time for Beckley WV as recorded at the GISS station

Temperature change with time for Charleston WV as recorded at the GISS station

There is a drop in temperature for this station, which is more distinct than that for Beckley.

Temperature change with time for Huntington WV as recorded at the GISS station

This shows more clearly the peak and fall of temperature until about 1965, followed by a weak rise which we have seen in the states to the South along the Atlantic.

Looking at the average USHCN temperatures, using the homogenized data set, there is relatively little temperature change for the state over the century, though the drop and then recovery of temperatures shown in the GISS data also holds for this series.

Average temperature in the state of West Virginia since 1895 using the homogenized temperatures from the USHCN.

The temperature rise in that time has been 0.04 degrees per century, which is hardly significant. Looking at the Time of Observation corrected raw data for the state:

Average temperature in the state of West Virginia since 1895 using the raw temperatures modified to account for the time of observation, from the USHCN.

West Virginia is 240 miles long and 130 miles wide, running from 77.67 deg W to 82.67 deg W, and from 37.17 deg N to 40.67 deg N. The mean latitude is 38.6 deg W, that of the USHCN stations is 38.8 deg N, and that of the GISS stations is at 38.17 deg N. The highest point in West Virginia is at 1,482 m at Spruce Knob, while the lowest is at 73 m on the Potomac. The average elevation is at 457.2 m. The average elevation of the USHCN stations is 369.8 m, while that of the GISS stations is 364.8 m.

All the stations save Pickens WV were in the citi-data set, for Pickens which was too small, I had to get the population (125) from Zip-codes.com.

Looking at the effect of geography on temperature for the state:

The effect of station latitude on temperature in West Virginia

Looking at the effect of longitude, as I have mentioned several times earlier, this is an artifact of elevation changes, included now only for completeness.

The effect of station longitude on temperature in West Virginia

As one sees the temperature, which fell with longitude on the other side of the mountains, now rises with longitude as the mountains reduce in size to the west. The correlation is with elevation:

The effect of station elevation on temperature in West Virginia.

Looking at population, the GISS stations, as is the apparent custom in the states around the Union, are located in cities with the largest population of the stations recorded for the state. The average population is 38,718, while the population around the USHCN stations is 9,872. (That would make a difference of perhaps 0.6 deg F). As a reminder the citi-data information on population is relatively recent, and I have correlated it with the average of the temperature at the stations over the past 5-years.

The effect of adjacent population on the station temperature in West Virginia.

Finally a look at the effect that homogenization of the data has on the average values:

Changes in average station temperature as a result of homogenizing the data.

The impact is focused around 1955, before then the homogenization increasingly added temperatures the further from that date, and similarly from that time forward. Wonder why?

OGPSS - Natural gas production, as shale gas arrives

The natural gas industry in the United States has undergone significant changes in the last twenty years. As I noted last time, until 1993 the industry was beset by regulation that controlled both price and flows. With the removal of those regulations the industry was able to make considerable strides to increase market share. As it became able to do so, the problems perceived from the burning of coal in particular as a power plant fuel, led to moves to increase the amount of electricity that is produced using natural gas. By 2009 the installed capacity to generate electricity included 34% that could be supplied from natural gas.

Sources for installed electricity generating power 2009 (Newell EIA )

The EIA further anticipate that over the next 25 years that natural gas will continue to dominate new plant construction, comprising about 60% of the 223 gigawatts anticipated, with wind, at 11% coming second, while other renewable sources (which include a number of varieties) has about 12% of the growth. Now that doesn’t mean that the US actually produces 34% of its power from natural gas. In fact it is down at around a quarter of the current total, the difference being that companies prefer to use nuclear and coal -fired stations for their base load, and use natural gas more to meet variations in the demand cycle.

Because of this increased use US natural gas consumption has been rising in the past few years.

U.S. natural gas consumption over the past decade (EIA) Note that 68 bcf/day is equivalent to 24.8 Tcf per year.

The total withdrawals of natural gas from domestic sources in 2009 totaled 28 trillion cubic feet (Tcf) of which 78% came from domestic gas wells, and 22% from oil wells. 13% of the 2009 total came from shale gas wells, and 8% from coal beds. Of the gas produced some 14% was re-injected to help maintain pressure in producing wells, and about 1% was flared. 3% of the volume was of non-hydrocarbon gases. The United States also imports around 11% of the gas that is consumed.

I am indebted to Gail Tverberg for the following plot that shows the longer trend in production, as well as the price (note that the difference in production volumes, relative to my numbers above, is that the figure below is just for natural gas wells).

Production of natural gas from US wells, and price of that NG. (Gail Tverberg)

Natural gas production by State, which I previously just ranked, shows that Texas continues to be primary, but that the combination of states outside of the big 5 is rising steadily.

Production of natural gas from different states (source EIA ).

It is worth noting that New Mexico, Oklahoma, Wyoming and the Federal offshore Gulf of Mexico (GOM) are declining while Louisiana is showing the greatest growth. In fact it is so great that Cheniere Energy will convert their LNG plant in the state so that it will be able to export Liquefied Natural Gas (LNG) rather than just store and re-gasify supplies after they have been imported. The hope is to have it on line and allowing the export of LNG by 2015. That growth in production has come largely from the development of the natural gas found in the Haynesville shale.

Location of the Haynesville gas shale drilling (Geology.com )

It was in February of this year that the Haynesville took over the lead in gas production from the Barnett Shale in Texas producing 5.5 bcf/day to the Barnett’s 5.25 bcf. The field has more than a thousand wells in production, with around 2,000 permitted, and over 500 having been drilled but not completed. Part of the more rapid success of the Haynesville, the first successful well was only 3 years ago, has been because the gas could be fed more easily into existing pipelines than the case in Texas. The well location lies south of Shreveport.

The EIA plot of drilling activity in the gas shales shows the growing popularity of the Eagle Ford and Marcellus, presaging future production increases and a challenge to Louisiana.

Drilling activity in the gas shales of the United States (Smith International via EIA )

The changing emphasis also is an indicator that the day of the Barnett shale appears to now be passing into afternoon.

Production from the different gas shales (EIA Newell )

One of the big questions, however, with gas shale production relates to how long they will continue to produce if the production decline rates fall at levels of 85% per annum that have been reported in the past. The long term production from these fields also depends on their profitability, and in this regard it is interesting to see how the EIA sees the price of natural gas moving over the course of the next 25 years.

EIA price projections for natural gas made in the past three years (EIA )

One question, since this price ties in to the volumes of gas that will be produced, continues to lie in the costs required to produce and transport the gas. If that remains below the selling price, and the new estimate price would appear to keep that distinction for the full 25 years, then the amount of gas produced will be much less. The EIA appear to hang their hat on long term sustained production from these wells. That may not be as true for the tighter shale rock than it is for more conventional gas reservoirs of the country.

The EIA has just noted, in their Energy Today post that stripper gas wells produce 11% of the volume of natural gas produced in the United States.

Individual natural gas stripper wells produce no more than about 90 thousand cubic feet of natural gas-equivalent per day over a twelve-month period (some wells also produce natural gas liquids), but because there are so many (nearly 340,000) they collectively account for a significant portion the Nation's total natural gas production—2,912 billion cubic feet, or over 11% in 2009.

Stripper well numbers and contribution to US natural gas production (EIA)

To put the percentage in context, one should also look at the volumes of natural gas that are being consumed and produced in the United States. Consumption over the past decade simplistically declined until 2006, whereafter it has increased, though the EIA now anticipate that it will now stabilize.

The 11% of volume thus translates to about 2 Tcf per year. They are most commonly found in Appalachia, Texas and Oklahoma. The roughly 300,000 stripper gas well total should be put in the context of a total of around 493,000 total gas wells in the USA in 2009.

There is likely thus to be some engagement in terms of the price of the product and thus volumes sold, between imported LNG, domestic conventional gas and shale gas. It will be interesting to see how that develops in the near future.

Katla continues to develop toward an upcoming volcanic eruption

The Icelandic press is reporting that there are ponds collecting as the ice in the Myrdalsjokull glacier continues to melt from the increasing heat coming from the underlying volcano, Katla, in Iceland. (h/t Jón Frímann ).

Collapsing ice cap above Katla (Iceland Review – English, and Icelandic ) (Remember that the black cover is because of the ash from Eyjafjallajokull last year)

As the fractures from the earthquakes continue to fracture to the surface, so the paths that they create allow water to migrate down to the underlying hotter rock. This then converts to steam, and flows back up helping to further melt the underside of the ice sheet, with some water possibly escaping down the mountain, under the ice. These floods can be sudden, as was the one that took out the ring road around Iceland. That has now been repaired, a week after the flood took it out.

The narrowness of the fracture paths, at least initially, will slow magma migration and this will likely allow more additional activity at the surface, although Katla does not give a lot of warning before it erupts, apparently.

One of the misfortunes of having retired and given away many of my books is that I no longer have the references that relate quake size to rock damage. A lot of this work was done in the South African gold mines, which go down over 3 km (2 miles) and are thus at the depths of many of the current quakes around Katla. As the mines extended the workings so the weight of the surrounding rock shifted, and the speed of this (usually following a mine blast with explosives that broke out some rock) would cause rock fracture in the area.

Quakes could be created that were up to a magnitude 4, similar to some of those around Katla recently, and resulted in significant rock movement and fracture. Underground this leads to problems with keeping the tunnels open and safe for the workers (since the rock bursts can be violent and hurl rock fragments a long way, as well as creating air blasts that can also be dangerous). There have also been larger ones.

But I was trying to get some sense of displacement and damage as a function of seismic strength, since when the rock fractures there is often some crushing of the rock along the interface of the fracture, and this would then be removable by the upward pressure of magma, and the fractures released the overlying confinement. The initial crushed zone probably measures just a few inches, but will be eroded out by water/steam passage and the later passage of magma, since fractured rock is easily removed. This then gives the open passages for magma to move. If the fractures intersect then the intervening rock will likely also be removed since the magma has a higher density and thus more power than mere water or steam flows. There have now been several dozen quakes within the region of the Katla caldera, and knowing the damage zone from each would allow a better estimate of how damaged the rock is. Bear in mind that the re-healed fractures (healed by cooling magma) from earlier eruptions are likely the weakest links that are now failing and opening, and in the process, therefore rebuilding the network of passages that are needed for flow. The levels of permeability generated are orders of magnitude greater than that from a typical oil well.

Where the rock is attached to the overlying ice, then cracks in the rock can also occur in the overlying ice. And you may note that in the above picture apart from the circular rings of fractures, there are three well defined line cracks that cross the circular fractures. If you also look at the web cam you can see (in daylight) some of the lines where magma has flowed up to the surface in earlier eruptions (the picture shown in the last post).

So we now watch as the process continues to unfold.

Katla in Iceland is getting closer to a volcanic eruption

So what is the definition of “hours” that I should have used in anticipating the Katla eruption in my last post on this subject? I must confess that I had anticipated about 72 hours being the likely envelope within which we would see an eruption following the magnitude 3 quake that happened there on Wednesday. But here we are just into Monday, and there has been no eruption yet. But there has been another magnitude 3.8 quake, in this case:

07-18-2011 63.660 -19.116 3.8 magnitude (1.1 km deep 7.0 km ENE of Godabunga)

There have been a flurry of small quakes, that had both preceded the current larger one, and which have now followed it (at least a dozen).

Katla earthquakes of the last 24-hours. The green star denotes the larger earthquake referred to above (Icelandic Met Office)

In the 24 hours before this last there had been over a dozen other earthquakes within the caldera region. The stress is inducing more and more fractures into the rock (hence the earthquakes) and as these coalesce and the rock becomes fragmented in the region of previous magma flows, this creates the weakened channel along which the magma can force its way. Jón Frímann is not reporting any signs of the harmonics that signal significant magma movement at the moment though he suspects that the location of the quakes, now indicate that magma is making its way to the surface. Looking at the seismograph plot that he has there is no question that activity seems to be rising.

Just as a reminder there are two webcams on the site, one is here and the other is here. Neither is showing much yet.

Katla from second webcam at 12:33 am Eastern US time.

We shall see if this is just another step along the way, or if this is now at the point of erupting. But I suspect that it won't be before I get up in the morning, so goodnight!

UPDATE
Well looking at the cloud patterns this morning, if I wanted to stretch my imagination, they do suggest there may be some steam





But as I continue watching, it is purely an artifact of the light. And the scenes return to normal.

UPDATE 2 At the end of the day the sky is clear and there is nothing visible above the surfaces on eith webcam. And so we can relax for a little. The Icelandic Met Office is also saying that an eruption is not likely. However there continue to be a significant number of small quakes that are not just at the surface. Bear in mind that after fractures are created, if the magma is to get through them they have to be held open by the fluid pressure, and that has to work its way up as the magma migrates upwards, and this all takes time.

North Carolina combined temperatures

The last post in this series, on South Carolina, brought up an unexpected temperature variation that, coincidentally, was being discussed both at Real Climate and at Climate Audit. The controversy at those two sites relates to the dip in sea surface temperatures (SST's) prior to 1970, and how accurately these were measured with the controversy relating to how many ships used a thermometer stuck into a bucket to measure the temperature, and how many used a measure of the temperature made at the inlet for the engine cooling water. Not wishing to step into that argument at the moment, what is interesting to me is that while the temperatures in Georgia and South Carolina showed a drop in temperatures over the same period and a quick check shows some drop in Maine, and Vermont, but looking at Massachusetts it seems more that the higher temperatures of around 1950 are the aberrant ones. But these are land-based and therefore not subject to the variations based on how the water was collected and held. So we will see how this pans out for North Carolina.

Location of the USHCN stations in North Carolina

North Carolina has the same number of USHCN stations as South Carolina (29) but it also has four GISS stations (whereas SC had none). The four stations are at Asheville (with data from 1903, a complete set from Charlotte, Greensboro has only data from 1948 on, and Raleigh. The average of the GISS stations shows the same drop that occurred in the states further South.

Average temperature in the state of North Carolina as a function of time, using the GISS station average.

Comparing this to the homogenized data from the stations in the USHCN, the drop is found, using the larger number of stations in that set of stations.

Average temperature in the state of North Carolina as a function of time, using the USHCN homogenized temperature average.

Average temperature in the state of North Carolina as a function of time, using the Time of Observation (TOBS) adjusted raw temperature average.

North Carolina is some 500 miles long and 130 miles wide. It runs from 75.5 deg W to 84.25 deg W, and from 34 deg N to 36.35 deg N. The central latitude is at 35.60 deg N. That of the GISS stations is at 35.65 deg N, while the USHCN is at 35.6 deg N. The state rises from sea level to 2,037 m, with a mean elevation of 213.4 m. The average GISS location is at 312.7 m, while that of the USHCN stations is at 260 m.

Looking to find the population around the different stations, Cape Hatteras is more the name of the barrier island than the community, so I checked with Google Earth:

Location of the USHCN station on Cape Hatteras near Frisco.

Frisco, checking with U.S. Beacon has a population of 401, though that was in 2000 and seems, from the photo, to be low.

And Transou does not appear in citi-data, so I also went to Google Earth for it. Looking around I decided it should have a population of about 50, although it turns out to be relatively close to Laurel Springs (population 1,400).

Location of Transou station in North Carolina – while there are lots of plots ready for housing development there are not a lot of houses yet.

The population around the GISS stations averages 361,732, while that of the USHCN stations is 61,431. That population difference might have caused a 0.47 deg difference making the GISS temperatures higher, while the difference is actually 0.22 degrees. That would be more than explained (about 0.5 deg) by the difference in elevation between the two averages.

Looking at the changes in temperature with location, North Carolina has the usual relationship with latitude:

Effect of latitude on average annual temperature in North Carolina

The state rises fairly significantly to the west:

Effect of longitude on average annual temperature in North Carolina

However the temperature fall is more likely correlated with elevation (since it goes down on the other side of the mountains).

Effect of elevation on average annual temperature in North Carolina

Looking at the population effect, and considering the average temperature over the past 5 years as the dependent variable:

Effect of local population on average temperature in North Carolina

Well it seems clear that the steep drop in temperatures around 1950 occurred in North Carolina also, so does it still hold true further north?

Oh, and that drop does not show up when one subtracts the TOBS data from the homogenized USHCN values, that adjustment is more linear.