A paleosecular variation (PSV) curve for western North America is presented on the basis of 94 virtual geomagnetic poles (VGPs) from dated volcanic rocks sampled at 446 sites. Approximately 60% of the paleomagnetic database has been previously published. A curve defined by “spherical smoothed splines” is fitted to the VGPs, ranked by the quality of the age determinations, where the data density is highest between 3690 and −30 years before present (B.P.) (A.D. 1950), between 7800 and 7050 years B.P., and between 14,060 and 12,700 years B.P. The younger segments of the curve derived from volcanic rocks are similar but less complex than other high‐resolution PSV curves derived from lacustrine sediments, particularly the record at Fish Lake, Oregon. The PSV record from lava flows (PSVL), however, is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14C dates. The new PSVL record provides a partial Holocene master curve for western North America and will be of particular value in dating geological and archeological materials using paleomagnetic directions.

The Heise and Picabo volcanic fields of eastern Idaho are part of the more extensive time-transgressive Yellowstone-Snake River Plain hotspot track. Calderas associated with these two silicic volcanic fields are buried under 1 to 3 km of younger basalt, so their locations and eruption record histories have been based on analysis of silicic units along the margins of the eastern Snake River Plain along with some limited geophysical data. A 1.5 km borehole penetrating through basalt into underlying silicic rocks provides new data we used to reassess caldera locations and the timing of eruptions of these volcanic fields. Using these new caldera locations, we calculate an extension-adjusted rate of 2.35 cm/yr for the North American plate over the last 6.66 m.y. and a velocity of 2.30 cm/yr over the 10.27 m.y. Recalculation of a previously determined plate velocity-based migration of the deformation field surrounding the eastern Snake River Plain yields an extension-adjusted rate of 2.38 ± 0.21 cm/yr. These migration rates all fall within the previously published range of North American plate velocities of 2.2 ± 0.8 cm/yr, 2.4 cm/yr, and 2.68 ± 0.78 cm/yr based on a global hot spot reference frame. The consistency of these rates suggest that over the last 10 m.y., the Yellowstone hot spot is fixed with respect to the motion of the North American plate and therefore consistent with a classical deep-sourced hotspot model.

A series of uniformly tilted fault‐bounded blocks is a common feature in actively extending regions, such as the Basin and Range province. If the tilted blocks were produced by rigid “domino‐style” rotation, one would predict large voids at either end of a series of these blocks. Using tilt data and a simple flexural calculation, we suggest that much of the apparent rigid behavior could also be produced by internal block deformation. In our model of normal fault growth, isostatic/elastic uplift of the footwall is coupled with hanging wall downdrop within the region between faults, resulting in the appearance of a tilted rigid block. We present tilt data sampled at varying distances from several block‐defining faults within the northeast Basin and Range province. Tilt measurements between a series of 30‐km spaced block‐defining faults are found to be uniform, while tilts between more widely spaced faults exhibit a pattern of tilt that diminishes to zero in less than 30 km. Using a simple flexural calculation for internal block deformation, we show that for this region the patterns of tilt are consistent with a flexural length scale of ∼8–12 km and deflections of 2–4 km. These estimates are compatible with both the lower limit to seismicity and basin depth determined from earthquake and seismic reflection studies.

Birds can navigate accurately over hundreds to thousands of kilometres, and this ability of homing pigeons is the basis for a worldwide sport. Compass senses orient avian flight, but how birds determine their location in order to select the correct homeward bearing (map sense) remains a mystery. Also mysterious are rare disruptions of pigeon races in which most birds are substantially delayed and large numbers are lost. Here, it is shown that in four recent pigeon races in Europe and the northeastern USA the birds encountered infrasonic (low-frequency acoustic) shock waves from the Concorde supersonic transport. An acoustic avian map is proposed that consists of infrasonic cues radiated from steep-sided topographic features; the source of these signals is microseisms continuously generated by interfering oceanic waves. Atmospheric processes affecting these infrasonic map cues can explain perplexing experimental results from pigeon releases.

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The 40 Ar/ 39 Ar investigations of a large suite of fi ne-grained basaltic rocks of the Boring volcanic fi eld (BVF), Oregon and Washington (USA), yielded two primary results. (1) Using age control from paleomagnetic polarity, stratigraphy, and available plateau ages, 40 Ar/ 39 Ar recoil model ages are defi ned that provide reliable age results in the absence of an age plateau, even in cases of signifi cant Ar redistribution. (2) Grouping of eruptive ages either by period of activity or by composition defi nes a broadly northward progression of BVF volcanism during latest Pliocene and Pleistocene time that refl ects rates consistent with regional plate movements. Based on the frequency distribution of measured ages, periods of greatest volcanic activity within the BVF occurred 2.7-2.2 Ma, 1.7-0.5 Ma, and 350-50 ka. Grouped by eruptive episode, geographic distributions of samples defi ne a series of northeast-southwest-trending strips whose centers migrate from south-southeast to north-northwest at an average rate of 9.3 ± 1.6 mm/yr. Volcanic activity in the western part of the BVF migrated more rapidly than that to the east, causing trends of eruptive episodes to progress in an irregular, clockwise sense. The K 2 O and CaO values of dated samples exhibit well-defi ned temporal trends, decreasing and increasing, respectively, with age of eruption. Divided into two groups by K 2 O, the centers of these two distributions defi ne a northward migration rate similar to that determined from eruptive age groups. This age and compositional migration rate of Boring volcanism is similar to the clockwise rotation rate of the Oregon Coast Range with respect to North America, and might refl ect localized extension on the trailing edge of that rotating crustal block.

Paleomagnetic data reflecting paleosecular variation (PSV) of the geomagnetic field are used to correlate individual lava flows in the lower east rift zone of Kilauea Volcano. This area has been recently mapped based on petrography, stratigraphy, soil development, and degree of weathering of the flows; eight 14C dates also provide a framework for the relative age assignments. Site‐mean directions of remanent magnetization for historic flows in this region indicate that local magnetic anomalies do not mask the PSV signal, that within‐flow angular differences are generally <5°, and that temporal resolution of the paleomagnetic directions is of the order of 100 years. The paleomagnetic correlations do not conflict with the observed stratigraphic relationships, and PSV reference curves from dated lava flows and lake sediments have also been used to help determine the sequence of directional groups. Paleomagnetic grouping of flows into eruptive events indicates a different and perhaps more refined eruptive history for the lower east rift zone than implied by the geologic mapping alone. The number of individual flows based on petrographic distinctions is likely the same, but the frequency of events (including petrographically distinct flows) is apparently lower than previously thought. Flows from ridge crest vents bifurcated by the rift indicate formation of the central graben in this region after ∼300 years ago, possibly related to the 1790 eruptions along dual fractures.