Kenneson G. Dean

Numerical modeling of lava flow cooling applied to the 1997 Okmok eruption: Approach and analysis

[1]xa0Throughout February and March of 1997 Okmok Volcano, in the eastern Aleutian Islands of Alaska, erupted a 6 km long lava flow of basaltic aa within its caldera. A numerical model for lava flow cooling was developed and applied to the flow to better understand the nature of its cooling. Radiation and convection from the surface, as well as conduction to the ground, were used to transport the flows heat to its surroundings in the model. Internally, a conduction-only approach moved heat from the interior outward. Vesiculation, latent heat generation, and thermal conductivity changes with temperature are among the other factors that were dynamically accounted for. Results indicate that ambient temperature fluctuations, on the scale of days to weeks, must be taken into account to create an accurate short-term prediction of lava surface temperature. Daily data of rainfall and ambient temperature, as opposed to yearly averages, greatly increased the accuracy of the model. Furthermore, convective cooling of the lava surface was observed to be a dominant heat loss process during the first 200 days, indicating the convective heat transfer coefficient is a prime determinant of the accuracy of the model for predicting surface temperatures. Over a longer cooling period (2 years), thermal conductivity and porosity proved to be among the dominating factors for heat loss because of the limiting role of conductive heat flow in the interior. The models flexibility allows application to flows other than the 1997 Okmok eruption.

Satellite analysis and PUFF simulation of the eruptive cloud generated by the Mount Etna paroxysm of 22 July 1998

[1]xa0We applied the PUFF algorithm [Searcy et al., 1998] to simulate the space-time evolution of the eruptive cloud generated by one of the main paroxysms to have occurred this past century at Etna volcano, namely the 22 July 1998 explosive event at the Voragine summit crater. The comparison of PUFF simulations to satellite images of the ash cloud at different times allowed us to estimate several parameters of the eruptive event, such as onset time, duration, ash cloud height and shape, and pyroclast size. Based on this analysis, we concluded that the paroxysm started around 1645 GMT, lasted between 20 and 40 min, and generated a Poissonian-shaped ash column nearly 13 km high and composed of particles with a mean diameter (MD) of 10−3 m and size logarithmic standard deviation (LSD) equal to 1.5. The PUFF simulations using horizontal and vertical diffusivity values of 5000 and 10 m2 s−1, respectively, provided the best agreement to the eruption clouds observed on satellite images. The results were compared to the information available in the literature concerning the eruption, e.g., volcanological, video camera, and volcanic tremor data. The analysis showed that the method of simulating the eruptive clouds and comparing simulations to satellite images can give a contribution to the study of paroxysmal events generated by the Etna volcano. Also, the degree of accuracy of the cloud simulation leads us to be optimistic about the potential of using this method as a tool for hazard mitigation in the Etna region, with particular applications to air traffic.

A river‐coastal sea ice interaction model: Mackenzie River Delta

It has been observed that arctic coastal regions which receive river discharge show significant ice regression in advance of other coastal areas without this source of sensible heat. This phenomena has been particularly apparent on satellite imagery. The work reported here attempts (1) to quantify and assess the influence of springtime river discharge on the removal of nearshore ice and (2) to demonstrate the utility of satellite imagery as a source of data to “drive” a model assessing the influence of springtime river discharge on the removal of nearshore ice. Central to this work is a sequence of advanced very high resolution radiometer images of the Mackenzie Delta region, Northwest Territories, Canada. These images constitute a database establishing the temporal sequence of observable breakup events from which a thermodynamic model for the ice decay can be parameterized. The emphases of this model are the influence of the riverine sensible heat on the melting of sea ice and the ability of satellite imagery to monitor this process. For simplicity, climatological values rather than meteorological values for atmospheric and solar influences have been used. The results suggest that the river discharge supplies a significant amount of sensible heat to the base of the nearshore ice, accounting for nearly half of the energy required to melt the ice cover. As a result, the coastal ice is removed 7–14 days in advance of areas without significant river discharge.

Aufeis in the Ivishak River, Alaska, mapped from satellite radar interferometry

Abstract Aufeis deposits form every year on many rivers on the North Slope of Alaska; and, through repeated episodes of overflow and freezing, they may reach a thickness of more than 3 m. The presence of aufeis in a drainage basin tends to stabilize river discharge in the same way as a glacier does, by providing melt water during hot dry periods. This distribution of aufeis deposits along the rivers is discontinuous because of variations in channel geometry and under-ice water supply, and monitoring their growth during the winter is generally impractical. However, experiments using satellite radar interferometry (SRI) to map changes in the extent of aufeis near the junction of the Ivishak and the Echooka Rivers in the northern Brooks Range during the winter have produced promising results. Interferograms of the area were made from pairs of images acquired by the European Space Agencys First Earth Remote Sensing Satellite in January through March 1994. The results indicate that aufeis deposits can be mapped on interferograms as areas in river valleys in which the radar phases are poorly correlated and radar backscatter values frequently change. The ability of SRI in monitoring subtle winter aufeis processes fills a major gap in the study of aufeis by remote sensing.

Active mud volcanism observed with Landsat 7 ETM

Abstract Mud volcanoes are relatively small spatter cones that erupt water-laden mud and gases, and occur throughout the world. For many mud volcanoes, the eruption of warm mud (10–40°C) can be detected with high-resolution thermal satellite imagery. We demonstrate the utility of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) imagery for thermal monitoring of active mud volcanism. We constrain the temperature and area of active mud discharge and estimate surface heat flux for two isolated mud volcanoes in the Copper River Basin, Alaska using Band 6 (10.4–12.5 μm). The heat flux results span a wide range due to uncertainties in the environmental conditions at the time of image acquisition, but can be constrained to be less than 0.24 MW for each of the two mud volcanoes considering previously published field measurements. With this higher-resolution Band 6 on the ETM+ sensor, as well as the high-resolution thermal bands on the ASTER sensor, reliable monitoring of mud volcanism on this scale is possible for the first time.

Numerical modeling of lava flow cooling applied to the 1997 Okmok eruption: Comparison with advanced very high resolution radiometer thermal imagery

[1]xa0Throughout February and March 1997, Okmok Volcano, in the eastern Aleutian Islands of Alaska, erupted a 6-km-long lava flow of basaltic ′a′a within its caldera. In the first part of the study a numerical model for lava flow cooling was developed by Patrick et al. and applied to the flow to better understand the nature of its cooling. In this second part of the study, the model predictions for lava surface temperature over a 200-day cooling period were compared to advanced very high resolution radiometer (AVHRR) thermal imagery. Various methods were used to extract the subpixel lava temperature from the AVHRR pixel-integrated values, including the dual-band method and pixel merging. Inherent to these approaches is the multicomponent modeling of the lava surface temperature. Whereas active flows have been shown to have several thermal components, so, too, do flows undergoing extended cooling. Because of the dependence of the methods on the AVHRR instantaneous field of view (IFOV), the scan-dependent IFOV dimensions and overlap values were considered. Results from Patrick et al. indicate that convective heat loss from the surface largely controls surface temperature during extended cooling, but the functions governing this heat loss mechanism are poorly understood. AVHRR-derived temperatures from this part of the study suggest that values for the convective heat transfer coefficient for this flow were most commonly between 50 and 100 W m−2 K−1 and generally above 25 W m−2 K−1. These results are in agreement with previously measured values from the field but are significantly higher than those assumed in other remote sensing studies of cooling lava. Also, the AVHRR data corroborate the modeled prediction of seasonal warming of the lava surface.

Satellite imagery proves essential for monitoring erupting Aleutian Volcano

Mt. Cleveland is one of more than 40 active volcanoes in Alaska that is monitored by the Alaska Volcano Observatory (AVO). It is located on the western half of Chuginadak, a remote and uninhabited island in the east central Aleutians that lies 1526 km southwest of Anchorage. The closest inhabited community, Nikolski, is 75 km to the east on Umnak Island (Figure 1). n nMt. Cleveland erupted explosively on 19 February and on 11 and 19 March 2001. Because the volcano is not yet monitored with seismic, deformation, or other geophysical instruments, satellite imagery was the only effective tool for detecting and monitoring this activity. Eruption clouds and elevated surface temperatures were detected on multiple satellite data sets. The largest eruption was in February. This first eruption cloud and the subsequent wave of ash (Figure 1) that drifted across Alaska extended up to flight levels and prompted cancellation and re-routing of air traffic throughout the North Pacific region on 19 and 20 February.

Satellite surveillance of volcanic ash plumes, application to aircraft safety

The early phreatomagmatic and magmatic explosive activity of Redoubt Volcano, December 14–16, 1989, produced several ashladen eruption columns that caused significant damage to jet aircraft. n nThe major aircraft-ash incident occurred December 15 at 1150 AST, when a KLM Boeing 747 jet aircraft, enroute from Amsterdam to Anchorage with 231 passengers and 14 crew members, flew through an ash plume east of Talkeetna, Alaska, at an altitude of 7.5 km and experienced sudden shutdown of all four engines. For 12 minutes the jet glided steeply from 7.5 km to 3.5 km before the crew managed to restart the engines after seven or eight tries. The plane came within about 1500 m of the mountain tops before landing safely at Anchorage International Airport.

The plume of the Yukon River in relation to the oceanography of the Bering Sea

Abstract Physical and biological oceanography of the northern Bering Sea including the plume of the Yukon River were studied using satellite data in conjunction with shipboard measurements. The satellite data recorded by the NOAA Very High Resolution Radiometer (VHRR) and Advanced Very High Resolution Radiometer (AVHRR), and the Landsat Multispectral Scanner (MSS) and Thematic Mapper (TM) sensors were used to detect sea surface temperatures and suspended sediments. Shipboard measurements of temperature, salinity, and chlorophyll were acquired by the Inner Shelf Transfer and Recycling (ISHTAR) project and were compared to digitally enhanced and archived satellite images. Sea surface temperatures derived from satellite data were generally higher than field measurements. This difference was the likely result of microscale stratification of the water column, although other factors could have been involved also. Satellite data confirmed the known distribution of water masses in the region (Coachman et al., 1975). Upwelled water of oceanic origin (Anadyr Water) was visible as a cold surface plume running from Anadyr Strait north through western Bering Strait. In the east, warm Alaskan Coastal Water was prominent along the Alaskan coast including Norton Sound and the southeastern Chukchi Sea. Areal patterns of temperature, salinity, and phytoplankton distribution, determined from field measurements, agreed reasonably well with patterns of water mass distribution obtained from satellite images. Archived satellite images (1974–1978) were used to investigate the variability of the distribution of sea surface temperature and of the turbid plume of the Yukon River. Alaskan Coastal Water (ACW) first warms near the coast in June and the process extends seaward as summer progresses. Turbid water associated with discharge of the Yukon River progresses in the same fashion, extending northward across the entrance to Norton Sound. Maximum extent of the plume occurs in October. Anadyr Water flows north through Anadyr Strait past St. Lawrence Island; its extent is variable depending on mesoscale pressure and local wind fields.

Monitoring Volcanoes in the North Pacific

Part 1: Understanding Volcano Imagery 1. Introduction to Volcano Monitoring from Space 2. Real-time Operational Satellite Monitoring Techniques 3. Validity and Accuracy of Satellite Data: Atmospheric Effects 4. Elevated Surface Temperatures of Volcanoes 5. Imaging of Volcanic Plumes 6. Gas Emissions from Volcanoes 7. Radar Interferometry (INSAR): A Long-term Monitoring Tool 8. Manned Missions Capturing Volcanic Activity 9. Volcanic Cloud Dispersion Models 10. False Alarms and No Alarms 11. View from the Cockpit 12. Regional and Global Impacts of Volcanic Eruptions in Satellite Imagery 13 Acquiring Satellite Data Part 2: Atlas of Imagery from the North Pacific Thermal Imagery Radar Imagery Space Shuttle Data and Imagery Regional and Global Impact of Eruptions