What Do You Understand
by Deccan Trap?
A student guide to understanding the Deccan Traps — what they are, how they formed, why they matter geologically, and how to approach assignments and exam questions that ask you to explain this massive flood basalt province and its role in one of Earth’s most debated extinction events.
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Get Expert Help →What Is the Deccan Trap? The Definition Your Assignment Needs to Start With
The Deccan Trap is one of Earth’s largest flood basalt provinces — a vast accumulation of horizontally layered basaltic lava flows covering approximately 500,000 square kilometres of the Deccan Plateau in west-central India. Formed primarily between 66 and 60 million years ago through repeated, massive volcanic eruptions driven by a mantle plume, the Deccan Traps produced an estimated 1 million cubic kilometres of lava. They are scientifically significant for their geological scale, their temporal coincidence with the Cretaceous-Paleogene (K-Pg) mass extinction, and what they reveal about the mechanisms of large igneous province (LIP) emplacement and its environmental consequences.
That question — “what do you understand by Deccan Trap?” — is not asking you to list facts. It is asking you to demonstrate conceptual understanding. That means explaining what kind of geological feature it is, how it came to exist, what its physical properties are, and why it matters. An answer that only gives a location and a date is incomplete.
Start with the geological category — flood basalt province, part of the large igneous province (LIP) family. Then explain the mechanism. Then the scale. Then the significance. That order reflects genuine understanding rather than rote memorisation, and it is the order that earns marks at degree level.
Trap vs. Traps — Singular and Plural Usage
Both “Deccan Trap” (singular) and “Deccan Traps” (plural) are used in academic literature, often interchangeably. The singular form refers to the geological formation as a single entity or province. The plural is more commonly used in geological and volcanological literature to acknowledge the many individual lava flows that constitute the province. Either is acceptable in an assignment — but be consistent. Check what your course materials or question paper uses and match it.
Why Is It Called a “Trap”? The Etymology Students Always Miss
The word “trap” in this context has nothing to do with catching anything. It comes from the Swedish word trappa, meaning staircase or stairs. Look at the Deccan Plateau landscape and the reason becomes obvious. Repeated lava flows, each hardening to a different thickness and eroding at a different rate, produce a stepped, terraced topography — the land literally looks like a giant staircase from a distance.
This terminology is not unique to the Deccan. All flood basalt provinces share the same stepped landscape and, by geological convention, the same name. The Siberian Traps, the Columbia River Basalt, the Ethiopian Traps — all named for the same landscape feature. Mentioning this etymology in your assignment signals geological literacy. It is a small point but it separates students who have engaged with the topic from those who have lifted a definition without reading around it.
The geology is not subtle. Stand on the Deccan Plateau and the landscape tells you what happened — layer upon layer of basalt, each flow a separate eruption event, the whole stack recording millions of years of intermittent volcanic output on a scale nothing alive today has experienced.
— Adapted from volcanological field accounts of the Deccan PlateauLocation, Geographic Extent, and the States It Covers
The Deccan Traps occupy the Deccan Plateau — a large elevated tableland in the Indian subcontinent, bounded by mountain ranges on three sides and sloping generally eastward toward the Bay of Bengal. The main geographic extent today covers:
| Dimension | Detail | Academic Significance |
|---|---|---|
| Current aerial extent | ~500,000 km² — primarily Maharashtra, Gujarat, Madhya Pradesh, Karnataka, Andhra Pradesh | One of the largest exposed flood basalt provinces on Earth; provides extensive accessible outcrops for field study |
| Estimated original extent | ~1.5 million km² before erosion over 66 million years | Erosion has removed enormous volumes — the original province was roughly three times its current visible area |
| Thickness | Up to 2,400 m in the Western Ghats; thinner eastward | The Western Ghats represent the thickest exposed section — closest to the original vent region |
| Number of identifiable flows | Approximately 30+ individual flow sequences, grouped into formations | Each flow sequence represents a separate eruption event — used to reconstruct eruption chronology |
| Key stratigraphic sections | Western Ghats escarpment; Narmada-Tapti valleys; Saurashtra Peninsula | Most detailed stratigraphy available in these exposures; used in radiometric dating and geochemical studies |
| Mantle plume now located | Under Réunion Island, Indian Ocean | As the Indian Plate drifted northward, the plume’s surface expression moved — Réunion volcanism is the plume’s current manifestation |
Assignment Tip: Use Geospatial Reasoning, Not Just Facts
Do not just state that the Deccan Traps cover Maharashtra and Gujarat. Explain why the thickness decreases eastward (distance from the main vent area near the Western Ghats), why erosion has reduced the total extent, and what the modern Réunion hotspot tells us about the motion of the Indian Plate. That kind of connected spatial reasoning is what university-level geography and geology assignments reward.
How the Deccan Traps Formed: The Mantle Plume Mechanism
Formation is the mechanistic core of any Deccan Traps assignment. You need to explain the process, not just the outcome. Here is what your answer needs to address:
The Three-Stage Formation Model
Plume generation → surface expression → emplacement and cooling
Stage 1: Mantle Plume
A thermal mantle plume — a column of anomalously hot mantle material rising from the core-mantle boundary — reached the base of the lithosphere beneath what is now the Indian Plate approximately 67–68 million years ago. The plume head, on contact with the base of the tectonic plate, spread laterally and began melting the overlying mantle.
Plume head diameter: estimated hundreds of kilometres; temperature anomaly: ~200–300°C above ambient mantleStage 2: Flood Basalt Eruption
Partial melting of the mantle produced enormous volumes of low-viscosity basaltic magma. Unlike explosive silicic volcanism, this basalt was highly fluid — it erupted from fissures (elongated cracks) rather than point volcanoes and flooded the surface in vast sheets, each flow extending hundreds of kilometres across flat terrain before cooling.
Individual flow thickness: 10–30 m typical; some compound flows exceed 100 m; rates: possibly 1 km³/year during peak phasesStage 3: Plate Motion & Plume Tail
As the Indian Plate continued its rapid northward drift (among the fastest plate motions in geological history), it moved away from the fixed plume. The plume tail — now feeding smaller volumes to successive points on the moving plate — produced the Lakshadweep island chain and ultimately the modern Réunion Island volcanic system.
Indian Plate velocity: ~15–20 cm/year during Cretaceous — unusually fast; Réunion: the active plume manifestation todayA Contested Point: Plume vs. Non-Plume Models
The mantle plume model is the dominant explanation for the Deccan Traps, but it is not uncontested. Some geologists argue that edge-driven convection, lithospheric extension, or decompression melting following rapid plate motion can explain LIPs without invoking deep plumes. Your assignment will score higher if you acknowledge this debate rather than presenting the plume model as settled fact. Cite Courtillot et al. and the anti-plume arguments from Anderson & Natland for a balanced treatment.
One more factor worth raising: the question of eruption pulsing. The Deccan Traps did not erupt continuously. Radiometric dating — particularly high-precision U-Pb and Ar-Ar dating of individual flow sequences — shows that eruption was episodic, with at least two or three major pulses. The largest pulse, producing roughly 70–80% of the total volume, appears to have occurred in fewer than 1 million years — geologically instantaneous.
Physical and Petrographic Characteristics of Deccan Basalts
If your assignment is at undergraduate or postgraduate level in geology, you will need to go beyond “it’s basalt.” The physical properties of the Deccan lavas carry information about eruption conditions, magma source, and cooling history.
Tholeiitic Basalt Dominated
The bulk of Deccan lavas are tholeiitic flood basalts — iron and magnesium-rich, silica-undersaturated basalts typical of continental flood basalt provinces. Geochemical variation across formations (Kalsubai, Lonavala, Wai subgroups) records evolving magma source conditions and crustal contamination during ascent.
Pahoehoe-Dominant Flows
Deccan flows are predominantly pahoehoe — smooth, ropy-surfaced lava formed by slow, sustained effusive eruption. This contrasts with the aa flows (rough, clinkery) common in more explosive settings. The pahoehoe character indicates low eruption rates and high temperatures, consistent with fluid, deep-source melts.
Intertrappean Beds
Between individual lava flows, “intertrappean beds” — thin sedimentary and volcaniclastic deposits — record periods of volcanic quiescence. These beds sometimes contain fossils and palaeosols (fossil soils), allowing correlation with biological and climatic events during the eruption sequence, including the K-Pg boundary horizon.
SiO₂ content: ~45–52 wt% — mafic, not intermediate or silicic
MgO: ~5–12 wt% — varies with crystallisation and crustal contamination
Sr isotope (⁸⁷Sr/⁸⁶Sr): 0.704–0.720 — elevated in some formations, indicating crustal assimilation
Dating methods used: Ar-Ar, U-Pb zircon (in interbedded tuffs), palaeomagnetic polarity stratigraphy
Subgroups (W. Ghats): Kalsubai (oldest) → Lonavala → Wai (youngest main phase)
Note: Formation names and boundaries remain subject to ongoing revision as dating precision improves
Large Igneous Provinces (LIPs): Where the Deccan Traps Fit Globally
Calling the Deccan Traps a “flood basalt” is accurate but incomplete without placing them in the Large Igneous Province (LIP) framework — the classification system used in modern volcanological and geodynamic literature. Understanding LIPs is essential for any university-level assignment on the Deccan Traps.
A Large Igneous Province is defined as an accumulation of mafic igneous rocks — basalt and related intrusive rocks — with an areal extent greater than 100,000 km² and a volume exceeding 100,000 km³, emplaced over a geologically short time interval (typically less than 5 million years). LIPs include continental flood basalts (like the Deccan Traps), oceanic plateaux, volcanic rifted margins, and ocean basin flood basalts.
| LIP Name | Age (Ma) | Volume (km³) | Associated Extinction | Plume Proposed |
|---|---|---|---|---|
| Siberian Traps | ~252 | ~3,000,000 | End-Permian (largest mass extinction) | Siberian plume |
| Central Atlantic Magmatic Province | ~201 | ~2,000,000 | End-Triassic extinction | CAMP plume |
| Karoo-Ferrar | ~183 | ~2,500,000 | Toarcian Oceanic Anoxic Event | Bouvet plume |
| Ontong Java Plateau | ~122 | ~44,000,000 | Aptian Oceanic Anoxic Event | Louisville plume |
| Deccan Traps | ~66 | ~1,000,000 | End-Cretaceous (K-Pg) | Réunion plume |
| Columbia River Basalt | ~17–6 | ~210,000 | Mid-Miocene disruption | Yellowstone plume |
The pattern in that table is striking and it is the central question in LIP research: do large igneous provinces cause mass extinctions? The coincidence of multiple LIPs with extinction events is not random — but whether it reflects causation or correlation, and what the mechanism would be, is what your essay needs to grapple with rather than assume.
The Deccan Traps and the K-Pg Extinction: Impact vs. Volcanism vs. Both
This is the question that makes the Deccan Traps famous outside geology departments. The end-Cretaceous mass extinction — 66 million years ago — killed approximately 75% of all species, including all non-avian dinosaurs. Two major hypotheses have competed to explain it, and the Deccan Traps sit at the centre of one of them.
Three Positions in the K-Pg Extinction Debate
Impact alone · Volcanism alone · Combined (current consensus direction)
Impact Hypothesis
The Chicxulub impactor — a ~10 km asteroid — struck the Yucatán Peninsula 66.043 Ma, triggering impact winter, acid rain, and wildfires. The iridium anomaly at the K-Pg boundary worldwide, shocked quartz, spherules, and the Chicxulub crater itself provide hard physical evidence.
Key evidence: Iridium anomaly (Alvarez et al. 1980), Chicxulub crater confirmation (1991)Deccan Volcanism Hypothesis
The main Deccan pulse (Phase 2) released massive CO₂ and SO₂ over tens of thousands to hundreds of thousands of years, causing prolonged climate disruption — warming, ocean acidification, and ecosystem stress — before and during the K-Pg boundary. Volcanism may have stressed ecosystems, making them vulnerable to collapse from the impact.
Key evidence: Timing of main pulse matches K-Pg; SO₂ emissions modelling; marine carbonate dissolutionCombined / Sequential Model
Growing evidence suggests the asteroid impact may have intensified Deccan volcanism via seismic shaking — Richards et al. (2015) proposed that the Chicxulub impact triggered enhanced lava output in the Deccan eruption sequence. The extinction may reflect cascading environmental stresses from both sources acting in sequence.
Key evidence: Ar-Ar dating showing eruption surge post-impact; correlation of lava pulse with K-Pg boundary layerDo Not Present This as Settled — The Debate Is Active
Students writing about the K-Pg extinction and the Deccan Traps often make one of two errors: treating the Chicxulub impact as the complete, unchallenged explanation (it is not — volcanism is a serious scientific hypothesis) or overclaiming for volcanism as the primary cause. The current literature — particularly work by Schoene et al. (2019) in Science and Sprain et al. (2019) also in Science, which reached different conclusions from different dating approaches on the same rocks — shows genuine disagreement. Present both positions with their evidence and acknowledge that the combined model is gaining traction but is not consensus.
🔥 Key Arguments in the Deccan Volcanism Extinction Debate
High-precision U-Pb dating (Schoene et al. 2019) places the main Deccan pulse within ~50,000 years of the K-Pg boundary — close enough to be causally significant
Sulphur dioxide and CO₂ released by Deccan eruptions at estimated rates would have caused aerosol-driven cooling and then greenhouse warming — documented in ocean sediment chemistry
Marine fossil records show declining diversity in some groups (planktic foraminifera, ammonites) before the K-Pg boundary — suggesting ecosystem stress predating the impact
The Chicxulub impact was effectively instantaneous. Geological and biological evidence supports a rapid, catastrophic extinction — more consistent with impact than with prolonged volcanism
The Siberian Traps (End-Permian) were far larger than the Deccan Traps and caused a far larger extinction. If Deccan volcanism alone had caused K-Pg, why was the extinction proportionally smaller than for Siberian?
Richards et al. (2015, Journal of the Geological Society) proposed that Chicxulub’s seismic energy triggered intensification of Deccan volcanism — making the two events physically linked, not just temporally coincident
Climate and Environmental Impact: How 1 Million km³ of Lava Changes a Planet
Scale matters here. The Deccan eruptions were not like anything observable in human history. Understand the orders of magnitude before you write about climate impact.
Sulphur Dioxide and Aerosol-Driven Climate Disruption
Each major Deccan eruption pulse released enormous quantities of SO₂ into the stratosphere. SO₂ converts to sulphate aerosols that scatter incoming solar radiation, causing short-term cooling — “volcanic winter” analogous to nuclear winter. Individual eruption phases may have caused temperature drops of 2–5°C for decades. The 1991 Pinatubo eruption released 20 million tonnes of SO₂ and cooled global temperatures by ~0.5°C — Deccan eruptions may have released orders of magnitude more.
CO₂ and the Greenhouse Rebound
After aerosols settled (years to decades), the CO₂ released by eruptions remained in the atmosphere for hundreds of thousands of years, driving long-term warming. Late Cretaceous ocean sediment records show carbon isotope excursions and ocean acidification consistent with repeated CO₂ pulses from Deccan volcanism. The climate oscillated — cold pulses during eruption peaks, warming in between — creating highly unstable conditions for ecosystems already stressed by the impact.
| Environmental Effect | Mechanism | Evidence Type | Timescale |
|---|---|---|---|
| Short-term cooling | SO₂ → stratospheric sulphate aerosols → reduced solar insolation | Palaeoclimate modelling; comparison with modern eruptions (Pinatubo, Tambora) | Years to decades per eruption pulse |
| Long-term warming | CO₂ accumulation → enhanced greenhouse effect | Carbon isotope excursions in ocean sediment cores (δ¹³C records); carbonate dissolution horizons | Thousands to hundreds of thousands of years |
| Ocean acidification | CO₂ absorption by seawater → carbonic acid formation → reduced pH | Dissolution of calcareous microfossils at K-Pg boundary; reduced carbonate preservation | Thousands of years per CO₂ pulse |
| Acid rain | SO₂ + H₂O → sulphuric acid precipitation | Weathering signatures in intertrappean soils; theoretical modelling | Synchronous with eruption pulses |
| Mercury spike | Volcanic mercury released to atmosphere, deposited globally | Mercury (Hg) anomalies in K-Pg boundary sections worldwide — a geochemical fingerprint of volcanism | Synchronous with eruption; preserves in sediment record |
The Mercury Proxy — A Sophisticated Tool Worth Mentioning
Mercury anomalies in sedimentary sections have become a key proxy for identifying volcanic events in the geological record. Volcanoes are the primary natural source of atmospheric mercury, which is deposited globally in organic-rich sediments. Elevated Hg/TOC (mercury to total organic carbon) ratios at K-Pg boundary sections worldwide — in sediments deposited before the impact horizon — have been interpreted as a Deccan volcanic fingerprint. If your assignment covers geochemical evidence for Deccan volcanism, the mercury proxy is a current, research-active line of evidence that signals genuine engagement with the literature.
How the Deccan Traps Compare With Other Flood Basalt Provinces
Context sharpens understanding. The Deccan Traps are large — but they are not the largest flood basalt province, and knowing where they sit in the global LIP inventory helps frame arguments about their extinction potential.
Siberian Traps (~252 Ma)
~3× the volume of the Deccan Traps; associated with the End-Permian extinction — Earth’s most severe, eliminating ~95% of marine species. The benchmark for volcanic extinction causation.
CAMP (~201 Ma)
Central Atlantic Magmatic Province; associated with End-Triassic extinction. Fragmented across now-separated continents — demonstrates how flood basalts track tectonic history.
Deccan Traps (~66 Ma)
~1 million km³; associated with K-Pg extinction — the most studied and debated LIP-extinction link in earth science. The one your assignment is about.
Ethiopian Traps (~30 Ma)
Large LIP associated with East African Rift System; no major mass extinction linked, but significant regional environmental effects. Useful comparison case for studying LIPs without extinctions.
Columbia River Basalt (~17–6 Ma)
Youngest major continental flood basalt; well-studied eruption rates and environmental effects; provides the best analogue for modelling what large eruptions do to climate in the geological record.
Ontong Java Plateau (~122 Ma)
The largest LIP by volume (~44 million km³ — oceanic plateau); not associated with a mass extinction, challenging simple causal models linking LIPs to extinctions. A key complication for your argument.
The Ontong Java Plateau point deserves emphasis. It is the largest LIP on Earth by volume — roughly 44 times larger than the Deccan Traps — yet it is not associated with a major mass extinction. This complicates any simple argument that LIP size causes extinctions and forces more nuanced explanations involving eruption rate, gas composition, palaeoclimate context, and the vulnerability of the existing biosphere. Any assignment arguing for Deccan volcanism as an extinction cause needs to address the Ontong Java counter-example.
How to Structure Your Deccan Trap Essay or Assignment Answer
The question “what do you understand by Deccan Trap?” is an invitation to demonstrate the depth of your understanding — not a request for a Wikipedia summary. Here is how to approach it at different levels of depth.
Short Answer / Exam Question (200–400 words)
What to include and what to leave out
- Open with definition: flood basalt province, Large Igneous Province, western India
- Explain the name: “trap” from Swedish trappa = staircase, reflecting stepped topography
- State formation mechanism: mantle plume (Réunion hotspot); fissure eruptions; low-viscosity basalt
- Give key facts: ~500,000 km², ~1M km³, ~66–60 Ma, up to 2,400 m thick
- State significance: coincides with K-Pg extinction; debate about causal role
- Do not attempt to cover the full extinction debate — you will run out of words
Extended Essay (1,500–3,000 words)
What each section should do
- Introduction: definition, LIP framework, key significance — tell the reader what to expect
- Formation: mantle plume mechanism, Indian Plate motion, Réunion connection
- Physical characteristics: flow types, stratigraphy, geochemistry — show you have read beyond the textbook
- Environmental impact: volcanic gases, short- and long-term climate effects
- K-Pg debate: impact hypothesis, volcanism hypothesis, combined model — balanced, citing both sides
- Comparison: where Deccan sits in global LIP context; Ontong Java problem
- Conclusion: synthesise what the evidence shows and what remains contested
Dissertation Chapter / Research Paper
What distinguishes this level
- Engage directly with primary literature: Schoene et al. (2019), Sprain et al. (2019), Richards et al. (2015) — not just textbook summaries
- Address methodological debates: why do U-Pb and Ar-Ar dating of same rocks give different age-eruption histories?
- Discuss mercury proxy data and its limitations as a volcanic fingerprint
- Evaluate alternative formation models (non-plume hypotheses)
- Consider taphonomic and sampling biases in the fossil record that affect extinction interpretation
- Situate the Deccan Traps within current debates in LIP science, not just K-Pg literature
Thesis Statement Builder — Deccan Trap Essay Examples
Strong vs. weak opening arguments across different question framings
Common Mistakes Students Make Writing About the Deccan Traps
| # | ❌ Mistake | Why It Costs Marks | ✓ The Fix |
|---|---|---|---|
| 1 | Calling it a volcano or volcanic eruption (singular) | The Deccan Traps are not a single volcano — they are a flood basalt province produced by thousands of individual fissure eruptions over millions of years. Describing it as “a volcano” reveals a fundamental misunderstanding of the geological category. | Use “flood basalt province,” “large igneous province,” or “fissure eruption sequence.” Distinguish the Deccan Traps from point-source volcanic systems like shield volcanoes or stratovolcanoes. |
| 2 | Stating definitively that Deccan volcanism caused the K-Pg extinction | This overstates what the evidence shows. The relationship between Deccan volcanism and the K-Pg extinction is scientifically contested. Claiming causation as established fact will be marked down by any examiner familiar with the current literature. | Frame it as “may have contributed,” “evidence suggests a link,” or “the temporal coincidence has led researchers to propose.” Then cite both the supporting and challenging evidence. |
| 3 | Ignoring the eruption chronology debate | The central uncertainty in Deccan research is not whether eruptions happened but when the main pulse occurred relative to the K-Pg boundary — and different dating methods give different answers. Ignoring this shows you have only read textbook summaries, not the actual research. | Reference Schoene et al. (2019) and Sprain et al. (2019) explicitly — these two papers, published in the same issue of Science, reached opposite conclusions from different dating approaches on the same formation. |
| 4 | Treating the Chicxulub impact and Deccan volcanism as mutually exclusive explanations | The either/or framing of this debate is outdated. The emerging evidence — particularly the seismic triggering hypothesis — suggests both events may have been connected, and both contributed to the environmental crisis. Presenting it as a binary choice suggests you have not read post-2010 literature. | Present the combined model explicitly. Acknowledge that the asteroid impact and Deccan volcanism may have interacted — impact-triggered seismicity potentially intensifying eruptive output — as a hypothesis with growing supporting evidence. |
| 5 | Getting the “trap” etymology wrong or ignoring it | Some students write that “trap” refers to a geological trap (a structure that captures petroleum) or simply do not address the term. Neither is correct. The etymology is Swedish, not English, and relates to landscape morphology, not structural geology. | State clearly: “trap” derives from the Swedish trappa (staircase), referring to the stepped topography produced by differential erosion of stacked horizontal lava flows. |
| 6 | Using only web sources and not citing primary literature | At undergraduate level and above, an answer that cites Wikipedia, general encyclopaedias, or popular science articles without peer-reviewed sources will be marked down for evidential quality, regardless of factual accuracy. | Cite at minimum: Courtillot & Renne (2003) on LIPs and extinctions; Richards et al. (2015) on seismic triggering; Schoene et al. (2019) and Sprain et al. (2019) on eruption chronology. These are the field-defining papers. |
Key Sources for Deccan Trap Assignments
A credible geology assignment on the Deccan Traps needs to engage with peer-reviewed literature, not just textbooks. Here are the essential sources — free-access where possible.
Schoene et al. (2019) — Science
U-Pb dating of Deccan lavas showing that the main eruption pulse began ~250,000 years before the K-Pg boundary — key evidence for pre-extinction volcanic stress. One of the two landmark 2019 papers.
science.org — Schoene et al. 2019Sprain et al. (2019) — Science
Ar-Ar dating of the same Deccan formations, concluding the main pulse occurred after the K-Pg boundary — directly contradicting Schoene et al. The disagreement between these two papers is the live frontier of Deccan research.
science.org — Sprain et al. 2019Courtillot & Renne (2003) — C.R. Geoscience
The foundational review paper on LIPs and mass extinctions — establishes the statistical case for LIP-extinction coincidence and is cited by virtually all subsequent work in this area. Available through most university library databases.
ScienceDirect — Courtillot & Renne 2003Verified External Resource: USGS Large Igneous Provinces
The United States Geological Survey maintains authoritative resources on Large Igneous Provinces including the Deccan Traps. The USGS Volcano Hazards Program and associated publications provide scientifically reliable, freely accessible overviews of flood basalt provinces, their formation mechanisms, and geological significance. Use these to anchor your foundational definitions before moving to primary literature. Access at: volcanoes.usgs.gov and through the USGS Publications Warehouse at pubs.usgs.gov.